OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

On 03/12/2015 12:34, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc
these days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in
the past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you
caught that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

My favourite was the car audio cassette player, ie no record function.
It recorded vinyl record clicks on to any prerecorded tape played in there.
Answer at end of spoiler defeat, run of +








+













+










+













+



























The pinch wheel had a tiny piece of magnet fragment embedded in it

Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

My first computer was a Franklin Ace 1000 that was give to me broken. It
had complete schematics so I was able to trace out what was in fact a bad
reset signal going to the CPU. Pretty sure it was a 74S161 (something that
ran hot and wasn't LS series) that had to be swapped out and it was fine
again. Donor chip came from an arcade machine board. Looking that part up
I see it's a 4 bit counter- if that's correct it may have someting to do
with the video timing signals which were a weird hack in the Apple ][
which this machine was an improved clone of.

On 3/12/2015 11:34 PM, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc
these days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in
the past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you
caught that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

**I recall the first time (1980-ish) I discovered those fusible
resistors that go high after a few years. With no obvious signs of
distress. Now I just head straight for the buggers.

Then there's those low value (/=47 Ohms), 1/4W cracked carbon resistors
that go O/C when subjected to ca. 60+ Volts with no signs of burning
(Marantz 1200b, 240, 250M, 500 models). Over the years, I learned to
suspect any resistor over the value of 100k, if the circuit is
displaying some kind of mysterious fault that cannot be explained by a
semiconductor failure or cap leakage.

--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On Fri, 4 Dec 2015 06:49:10 +1100, Trevor Wilson
wrote:

On 3/12/2015 11:34 PM, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc
these days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in
the past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you
caught that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

**I recall the first time (1980-ish) I discovered those fusible
resistors that go high after a few years. With no obvious signs of
distress. Now I just head straight for the buggers.

Then there's those low value (/=47 Ohms), 1/4W cracked carbon resistors
that go O/C when subjected to ca. 60+ Volts with no signs of burning
(Marantz 1200b, 240, 250M, 500 models). Over the years, I learned to
suspect any resistor over the value of 100k, if the circuit is
displaying some kind of mysterious fault that cannot be explained by a
semiconductor failure or cap leakage.
That resistor story is interesting. About two years ago I had a linear
power supply fail in one of my CNC machines. I did the troubleshooting
bit and discovered a bad -15 volt regulator. So I replaced it and then
a few weeks later something else went bad and I couldn't find it. I
took it to a friend who is an electronics engineer and he discovered
an open resistor. I asked why he checked it because there was no
visual reason for it to be bad. It wasn't cracked or discolored. He
said that's what he usually did first, check for open resistors. He
said it was a common fault. Since then the power supply has been
operating fine.
Eric

wrote in message
...
On Fri, 4 Dec 2015 06:49:10 +1100, Trevor Wilson
wrote:

On 3/12/2015 11:34 PM, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc
these days.

I "tune in" here almost daily and rarely find anything of interest to
me.

Maybe we could share some "war stories" of cool repairs we have done in
the past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you
caught that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

**I recall the first time (1980-ish) I discovered those fusible
resistors that go high after a few years. With no obvious signs of
distress. Now I just head straight for the buggers.

Then there's those low value (/=47 Ohms), 1/4W cracked carbon resistors
that go O/C when subjected to ca. 60+ Volts with no signs of burning
(Marantz 1200b, 240, 250M, 500 models). Over the years, I learned to
suspect any resistor over the value of 100k, if the circuit is
displaying some kind of mysterious fault that cannot be explained by a
semiconductor failure or cap leakage.
That resistor story is interesting. About two years ago I had a linear
power supply fail in one of my CNC machines. I did the troubleshooting
bit and discovered a bad -15 volt regulator. So I replaced it and then
a few weeks later something else went bad and I couldn't find it. I
took it to a friend who is an electronics engineer and he discovered
an open resistor. I asked why he checked it because there was no
visual reason for it to be bad. It wasn't cracked or discolored. He
said that's what he usually did first, check for open resistors. He
said it was a common fault. Since then the power supply has been
operating fine.
Eric



Yeah - when "the usual suspects" don't pan out, I start looking for bad high
value resistors.

Had a bad 150K 1/8 watt carbon on a late model Pioneer surround receiver the
other day.


Mark Z.

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

**I recall the first time (1980-ish) I discovered those fusible resistors
that go high after a few years. With no obvious signs of distress. Now I
just head straight for the buggers.

Then there's those low value (/=47 Ohms), 1/4W cracked carbon resistors
that go O/C when subjected to ca. 60+ Volts with no signs of burning
(Marantz 1200b, 240, 250M, 500 models). Over the years, I learned to
suspect any resistor over the value of 100k, if the circuit is displaying
some kind of mysterious fault that cannot be explained by a semiconductor
failure or cap leakage.

--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus



A brand new "war story".

As I am nearing the end of my career, I wonder if any one unit will be the
high water mark so far as feeling the satisfaction of fixing a really tough
one.

This may be it.

A Yamaha M-80 power amplifier. I've worked on a few in the past - difficult
but doable.

I've always thought that "M-80" was a humorously ironic model number for an
amplifier so flammable.

Initial inspection:

Burned resistors on both channels, a vented 1000uF 100v cap (one of a pair)
on the main board, lots of brown glue, some green corrosion visible on
component leads.

Strangely - only one output transistor was bad. I knew this was going to be
a tough one but I figured I could do it - just give the customer a pretty
high estimate.

Replaced those larger caps, lots of bad drivers, pre-drivers, signal
transistors, several burned and corroded resistors, one bias transistor.

Replaced the one bad output and it's mate. I figured the same current ripped
through both, so I wanted at least do that.

I knew the speaker relays would need service, so I took them out of order
and did that job.

Bringing up on a variac, the fires were out, bias adjusted OK, but no sound.
Another bad resistor.


Replaced this, but now there was a -86 volt(!) offset. Couple more bad
resistors.

Each time a component replaced it was necessary to monitor bias when
bringing it up.

Bring it up again, no offset but one channel oscillates. Fine. Trace down
and replace the bias transistor on that channel that was breaking down.
Replace it and: one channel low in gain, approximately 1/2 the other
channel.

Replace a bad 3.9K 1/2 watt resistor in the feedback loop. That was easy.
NOPE.

Now BOTH channels oscillate like crazy. Apparently a larger 3.9K 2W resistor
was corroded and got nudged while replacing the other. Replaced that. No
more oscillation. NOW:

Still no change on the gain problem.

Bad 430 ohm resistor hiding UNDER a power resistor, and not even visible
until the other was removed.

Unit now repaired and functioning properly.

This thing took approximately five whole days worth of bench time.

I'm going to spend a very generous amount of time patting myself on the back
for this one.


Mark Z.

On 3/02/2016 11:31 PM, Mark Zacharias wrote:
Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

**I recall the first time (1980-ish) I discovered those fusible
resistors that go high after a few years. With no obvious signs of
distress. Now I just head straight for the buggers.

Then there's those low value (/=47 Ohms), 1/4W cracked carbon
resistors that go O/C when subjected to ca. 60+ Volts with no signs of
burning (Marantz 1200b, 240, 250M, 500 models). Over the years, I
learned to suspect any resistor over the value of 100k, if the circuit
is displaying some kind of mysterious fault that cannot be explained
by a semiconductor failure or cap leakage.

--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus



A brand new "war story".

As I am nearing the end of my career, I wonder if any one unit will be
the high water mark so far as feeling the satisfaction of fixing a
really tough one.

This may be it.

A Yamaha M-80 power amplifier. I've worked on a few in the past -
difficult but doable.

I've always thought that "M-80" was a humorously ironic model number for
an amplifier so flammable.

Initial inspection:

Burned resistors on both channels, a vented 1000uF 100v cap (one of a
pair) on the main board, lots of brown glue, some green corrosion
visible on component leads.

Strangely - only one output transistor was bad. I knew this was going to
be a tough one but I figured I could do it - just give the customer a
pretty high estimate.

Replaced those larger caps, lots of bad drivers, pre-drivers, signal
transistors, several burned and corroded resistors, one bias transistor.

Replaced the one bad output and it's mate. I figured the same current
ripped through both, so I wanted at least do that.

I knew the speaker relays would need service, so I took them out of
order and did that job.

Bringing up on a variac, the fires were out, bias adjusted OK, but no
sound.
Another bad resistor.


Replaced this, but now there was a -86 volt(!) offset. Couple more bad
resistors.

Each time a component replaced it was necessary to monitor bias when
bringing it up.

Bring it up again, no offset but one channel oscillates. Fine. Trace
down and replace the bias transistor on that channel that was breaking
down. Replace it and: one channel low in gain, approximately 1/2 the
other channel.

Replace a bad 3.9K 1/2 watt resistor in the feedback loop. That was
easy. NOPE.

Now BOTH channels oscillate like crazy. Apparently a larger 3.9K 2W
resistor was corroded and got nudged while replacing the other. Replaced
that. No more oscillation. NOW:

Still no change on the gain problem.

Bad 430 ohm resistor hiding UNDER a power resistor, and not even visible
until the other was removed.

Unit now repaired and functioning properly.

This thing took approximately five whole days worth of bench time.

I'm going to spend a very generous amount of time patting myself on the
back for this one.


**All for an amp worth, what(?), $300.00? It can be a bugger of a
business. How much can you charge your client? $200.00?

On the flip side, I did a couple of really ancient (ca. 1972) Accuphase
amps recently. The client was willing to spend around $700.00 on each.
He bought them for a song and they typically sell for a couple of Grand
on eBay.


--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

"Trevor Wilson" wrote in message
...
On 3/02/2016 11:31 PM, Mark Zacharias wrote:
Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

**I recall the first time (1980-ish) I discovered those fusible
resistors that go high after a few years. With no obvious signs of
distress. Now I just head straight for the buggers.

Then there's those low value (/=47 Ohms), 1/4W cracked carbon
resistors that go O/C when subjected to ca. 60+ Volts with no signs of
burning (Marantz 1200b, 240, 250M, 500 models). Over the years, I
learned to suspect any resistor over the value of 100k, if the circuit
is displaying some kind of mysterious fault that cannot be explained
by a semiconductor failure or cap leakage.

--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus



A brand new "war story".

As I am nearing the end of my career, I wonder if any one unit will be
the high water mark so far as feeling the satisfaction of fixing a
really tough one.

This may be it.

A Yamaha M-80 power amplifier. I've worked on a few in the past -
difficult but doable.

I've always thought that "M-80" was a humorously ironic model number for
an amplifier so flammable.

Initial inspection:

Burned resistors on both channels, a vented 1000uF 100v cap (one of a
pair) on the main board, lots of brown glue, some green corrosion
visible on component leads.

Strangely - only one output transistor was bad. I knew this was going to
be a tough one but I figured I could do it - just give the customer a
pretty high estimate.

Replaced those larger caps, lots of bad drivers, pre-drivers, signal
transistors, several burned and corroded resistors, one bias transistor.

Replaced the one bad output and it's mate. I figured the same current
ripped through both, so I wanted at least do that.

I knew the speaker relays would need service, so I took them out of
order and did that job.

Bringing up on a variac, the fires were out, bias adjusted OK, but no
sound.
Another bad resistor.


Replaced this, but now there was a -86 volt(!) offset. Couple more bad
resistors.

Each time a component replaced it was necessary to monitor bias when
bringing it up.

Bring it up again, no offset but one channel oscillates. Fine. Trace
down and replace the bias transistor on that channel that was breaking
down. Replace it and: one channel low in gain, approximately 1/2 the
other channel.

Replace a bad 3.9K 1/2 watt resistor in the feedback loop. That was
easy. NOPE.

Now BOTH channels oscillate like crazy. Apparently a larger 3.9K 2W
resistor was corroded and got nudged while replacing the other. Replaced
that. No more oscillation. NOW:

Still no change on the gain problem.

Bad 430 ohm resistor hiding UNDER a power resistor, and not even visible
until the other was removed.

Unit now repaired and functioning properly.

This thing took approximately five whole days worth of bench time.

I'm going to spend a very generous amount of time patting myself on the
back for this one.


**All for an amp worth, what(?), $300.00? It can be a bugger of a
business. How much can you charge your client? $200.00?

On the flip side, I did a couple of really ancient (ca. 1972) Accuphase
amps recently. The client was willing to spend around $700.00 on each. He
bought them for a song and they typically sell for a couple of Grand on
eBay.


--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


After an initial assessment, I gave the customer an approximately 300.00
estimate.

Midway through the process I advised him it would be more.

Billed out at 400.00.

He hasn't picked it up yet, but it's part of a set with the preamp, tuner,
cd, and cassette so I'm not too worried.

Yeah - these days you take what you can get.

I was pretty confident I could fix it, but one problem kept hiding behind
the last one, and oscillation problems kinda turn my knees to jelly.


Mark Z.

On Thu, 4 Feb 2016 05:09:48 -0600, "Mark Zacharias"
wrote:

"Trevor Wilson" wrote in message
...
On 3/02/2016 11:31 PM, Mark Zacharias wrote:
Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

**I recall the first time (1980-ish) I discovered those fusible
resistors that go high after a few years. With no obvious signs of
distress. Now I just head straight for the buggers.

Then there's those low value (/=47 Ohms), 1/4W cracked carbon
resistors that go O/C when subjected to ca. 60+ Volts with no signs of
burning (Marantz 1200b, 240, 250M, 500 models). Over the years, I
learned to suspect any resistor over the value of 100k, if the circuit
is displaying some kind of mysterious fault that cannot be explained
by a semiconductor failure or cap leakage.

--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus



A brand new "war story".

As I am nearing the end of my career, I wonder if any one unit will be
the high water mark so far as feeling the satisfaction of fixing a
really tough one.

This may be it.

A Yamaha M-80 power amplifier. I've worked on a few in the past -
difficult but doable.

I've always thought that "M-80" was a humorously ironic model number for
an amplifier so flammable.

Initial inspection:

Burned resistors on both channels, a vented 1000uF 100v cap (one of a
pair) on the main board, lots of brown glue, some green corrosion
visible on component leads.

Strangely - only one output transistor was bad. I knew this was going to
be a tough one but I figured I could do it - just give the customer a
pretty high estimate.

Replaced those larger caps, lots of bad drivers, pre-drivers, signal
transistors, several burned and corroded resistors, one bias transistor.

Replaced the one bad output and it's mate. I figured the same current
ripped through both, so I wanted at least do that.

I knew the speaker relays would need service, so I took them out of
order and did that job.

Bringing up on a variac, the fires were out, bias adjusted OK, but no
sound.
Another bad resistor.


Replaced this, but now there was a -86 volt(!) offset. Couple more bad
resistors.

Each time a component replaced it was necessary to monitor bias when
bringing it up.

Bring it up again, no offset but one channel oscillates. Fine. Trace
down and replace the bias transistor on that channel that was breaking
down. Replace it and: one channel low in gain, approximately 1/2 the
other channel.

Replace a bad 3.9K 1/2 watt resistor in the feedback loop. That was
easy. NOPE.

Now BOTH channels oscillate like crazy. Apparently a larger 3.9K 2W
resistor was corroded and got nudged while replacing the other. Replaced
that. No more oscillation. NOW:

Still no change on the gain problem.

Bad 430 ohm resistor hiding UNDER a power resistor, and not even visible
until the other was removed.

Unit now repaired and functioning properly.

This thing took approximately five whole days worth of bench time.

I'm going to spend a very generous amount of time patting myself on the
back for this one.


**All for an amp worth, what(?), $300.00? It can be a bugger of a
business. How much can you charge your client? $200.00?

On the flip side, I did a couple of really ancient (ca. 1972) Accuphase
amps recently. The client was willing to spend around $700.00 on each. He
bought them for a song and they typically sell for a couple of Grand on
eBay.


--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


After an initial assessment, I gave the customer an approximately 300.00
estimate.

Midway through the process I advised him it would be more.

Billed out at 400.00.

He hasn't picked it up yet, but it's part of a set with the preamp, tuner,
cd, and cassette so I'm not too worried.

Yeah - these days you take what you can get.

I was pretty confident I could fix it, but one problem kept hiding behind
the last one, and oscillation problems kinda turn my knees to jelly.


Mark Z.

Mark,

These were the worst! I've seen 20 or more transistors blown on these
amps. I admire your tenacity. The Accuphases were so much easier to
repair.

---
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On 12/3/2015 6:34 AM, Mark Zacharias wrote:


C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

I posted this an hour ago, but it hasn't shown up, so I'll do it again.

Back 30 years ago I stopped at a consumer electronics/TV repair shop
and presented my resume. I had been to many manufacturer service
training seminars and had a hand full of certificates of completion. The
owner looked it over and said, "I just hired a guy, I wish you came in
earlier." So I went home and about 45 minutes later he called and said,
"I see you have a lot of Sony training, I have this projection TV in
here that nobody can fix, I'd be happy to pay you for looking at it."
So I drove down and got the manual, noted the problem was, no output
from the 3 tubes. I started poking around in the HV section, and within
minutes the owner said, hey you got it working! I didn't know it was
working ;-} I put my head out front and it had an output.
Hmm, I unhooked my scope probe and the picture went with it.
From there, we, more he, figured out one of the other techs replaced a
cap with 1/10 the proper value, the scope probe hanging on the test
point had enough capacitance to make the set work.
He hired me that day, it was good, within two blocks of my house.
So, I got a job by accident.
Mikek

One of my favorite stories is from electronics lab in college.

We had to build a small two stage transistor audio amp in the lab with parts from the stock room, onto a protoboard like breadboard.

My lab partners and I were experienced hams and got ours working in no time , no problems.

The PHD proffesor called me over to help him troubleshoot another groups that they could not get to work.

The design had a 10uf cap between the two stages.

I looked at the other groups breadboard and immediatly saw a tiny ceramic cap with a 10 printed on it between the two stages.

I pointed to the cap and said, that doesn't look right.

Got an A in that lab.

=========================

Oh another one.

I worked for a company that made CATV settop boxes.
I wandered into the lab where a group of young engineers were stuck troubleshooting a new box design. The picture was black and white and they could not figure out why there was no color. Looking into the box I saw a crystal marked 3.579545.

On a total whim, I put my fingers on the crystal.

The picture immediatly snapped into color!!!!

I was amazed myself but didn't let it show....I just cooly said, there is your problem and walked away. :-)



And lastly, in the same vein
you will all enjoy this story

http://www.rfcafe.com/references/pop...lectronics.htm

Have fun

Mark







Mark...
====================

On Fri, 4 Dec 2015 07:13:43 -0800 (PST), wrote:

One of my favorite stories is from electronics lab in college.

We had to build a small two stage transistor audio amp in the lab with parts from the stock room, onto a protoboard like breadboard.

My lab partners and I were experienced hams and got ours working in no time , no problems.

The PHD proffesor called me over to help him troubleshoot another groups that they could not get to work.

The design had a 10uf cap between the two stages.

I looked at the other groups breadboard and immediatly saw a tiny ceramic cap with a 10 printed on it between the two stages.

I pointed to the cap and said, that doesn't look right.

Got an A in that lab.

=========================

Oh another one.

I worked for a company that made CATV settop boxes.
I wandered into the lab where a group of young engineers were stuck troubleshooting a new box design. The picture was black and white and they could not figure out why there was no color. Looking into the box I saw a crystal marked 3.579545.

On a total whim, I put my fingers on the crystal.

The picture immediatly snapped into color!!!!

I was amazed myself but didn't let it show....I just cooly said, there is your problem and walked away. :-)



And lastly, in the same vein
you will all enjoy this story

http://www.rfcafe.com/references/pop...lectronics.htm

Have fun

Mark







Mark...
====================







For a very short time in the 1980s, Kenwood manufactured amplifiers
with wrong value resistors at various locations. The first one was a
bear because I had never seen a Japanese company make that kind of
mistake.

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On Saturday, December 5, 2015 at 4:30:21 PM UTC-5, Chuck wrote:
On Fri, 4 Dec 2015 07:13:43 -0800 (PST), wrote:

One of my favorite stories is from electronics lab in college.

We had to build a small two stage transistor audio amp in the lab with parts from the stock room, onto a protoboard like breadboard.

My lab partners and I were experienced hams and got ours working in no time , no problems.

The PHD proffesor called me over to help him troubleshoot another groups that they could not get to work.

The design had a 10uf cap between the two stages.

I looked at the other groups breadboard and immediatly saw a tiny ceramic cap with a 10 printed on it between the two stages.

I pointed to the cap and said, that doesn't look right.

Got an A in that lab.

=========================

Oh another one.

I worked for a company that made CATV settop boxes.
I wandered into the lab where a group of young engineers were stuck troubleshooting a new box design. The picture was black and white and they could not figure out why there was no color. Looking into the box I saw a crystal marked 3.579545.

On a total whim, I put my fingers on the crystal.

The picture immediatly snapped into color!!!!

I was amazed myself but didn't let it show....I just cooly said, there is your problem and walked away. :-)



And lastly, in the same vein
you will all enjoy this story

http://www.rfcafe.com/references/pop...lectronics.htm

Have fun

Mark







Mark...
====================







For a very short time in the 1980s, Kenwood manufactured
amplifiers with wrong value resistors at various locations. The
first one was a bear because I had never seen a Japanese company
make that kind of mistake.

Lawsuits over the years have shown their companies to be just as liable occasionally, too (like with Nomura, Sumitomo, Mitsubishi, Toyota, Honda, Mazda, Hitachi and others...) I think that things are done less purposely with regards to American markets, though.

wrote in message
...
On Saturday, December 5, 2015 at 4:30:21 PM UTC-5, Chuck wrote:
On Fri, 4 Dec 2015 07:13:43 -0800 (PST), wrote:

One of my favorite stories is from electronics lab in college.

We had to build a small two stage transistor audio amp in the lab with
parts from the stock room, onto a protoboard like breadboard.

My lab partners and I were experienced hams and got ours working in no
time , no problems.


At college I had a lab with the same thing. We designed simple circuits and
built them and took measurments on them. There were boxes of parts that
were suspose to be the same parts. Some of the parts were either bad or out
of spec. Not on purpose, they just got that way over the years. Me and a
person I was with usually could locate the bad parts and get our project
going first. Got to be a joke that the ones that got theirs to work had the
lucky box with all good parts for that design.

On Thursday, December 3, 2015 at 12:34:56 PM UTC, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.



My favourite - I was working for a Pro PA hire compoany in London. They had supplied a monitor system for a BBC recording of Public Image Ltd at Maida Vale Studios, London. The system was buzzing like crazy and none of the Sound Company or BBC engineers could work out why. They were about to pull the whole gig.
They sent me down as a last faint hope.

It was obviously some kind of mains problem, but everything seemed to check out fine on multimeters. Earths, Neutrals were all at 0v.
Eventually I decided to plug in my scope, to discover that instead of a nice straight line accross the display, it was massively modulated.
Clearly the scope's Earth wasn't a proper Earth but had some mains on it.
I then was able to track down the fault - one multi-way extension cable attatched to the many, many pieces of equipment had Earth and Neutral reversed, thus connecting all Earths and Neutrals in the middle of the studio as well as back at the mains Intake.

Ripped the offending extension out, the buzzing ceased immediately, and the BBC and Public Image Limited got their recording and the Sound Company didn't lose the gig or it's reputation.



Gareth.

wrote:


I then was able to track down the fault - one multi-way extension
cable attatched to the many, many pieces of equipment had Earth
and Neutral reversed, thus connecting all Earths and Neutrals
in the middle of the studio as well as back at the mains Intake.

Ripped the offending extension out, the buzzing ceased immediately,
and the BBC and Public Image Limited got their recording and the
Sound Company didn't lose the gig or it's reputation.



** I know of a similar example involving a 30kW, 3 phase lighting system for live entertainment here in Sydney. Was back when lighting consoles communicated
with triac dimmer racks via 0-10V analogue signals.

The system seemed to have a mind of its own, lights came up and varied about with all faders set to zero. Bringing one fader up affected many others.

After hours of fruitless searching, the culprit was identified as the AC plug on the lighting console itself which had neutral & earth reversed.

Seems a roadie had fitted a new plug after accidentally damaging the original and told nobody.


..... Phil

On Thu, 3 Dec 2015 06:34:55 -0600, "Mark Zacharias"
wrote:

OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.
The receiver tech was flummoxed by one of those large 1970s Pioneer
receivers. It had a problem none of us had seen before and we were a
high volume audio chain. There was slight audio distortion on both
channels, only on FM. We all worked commission only so I was the only
one to volunteer to help him out. To cut to the chase, the receiver
had an over designed mute circuit that was 3 or 4 stages deep, At the
deepest stage there was one of the Sanyo electrolytics that became a
common failure item many years later which was slightly leaky.

I've got another one. In the early 80s there were these 19" Hitachi
tvs that ghosted. It looked exactly like a bad delay line. By that
time I ran the TV service department for the same company. We had
just switched over to the big box store concept and I was inundated
with broken tvs. Out of desperation, I switched out the CRT and the
ghosting disappeared. We sold 1000s of these sets and I saw the
problem 3 more times.

And another. Kenwood sold these Funai made cd changers that never
worked properly. All of them would come back with skipping or not
playing discs problems. Kenwood came out with 3 or 4 mods, none which
worked. Sometimes they would work for months before they came back.
Somehow I found out if the mechanism retaining springs were stretched
so the mechanism didn't sag at all, the problem disappeared. Called
up Kenwood and they put out a mod kit that included strong springs
which also didn't allow any downward movement of the mechanism.

Last one. There were these very expensive ADS cd players which would
play any disc except a ,very popular at the time, Jimi Hendrix Ryko
disc. Couldn't find any electronic or mechanical problems. I slightly
moved the CD turntable slightly down on the spindle and this disc and
all other discs would play.

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"Chuck" wrote in message
...
The receiver tech was flummoxed by one of those large 1970s Pioneer
receivers. It had a problem none of us had seen before and we were a
high volume audio chain. There was slight audio distortion on both
channels, only on FM. We all worked commission only so I was the only
one to volunteer to help him out. To cut to the chase, the receiver
had an over designed mute circuit that was 3 or 4 stages deep, At the
deepest stage there was one of the Sanyo electrolytics that became a
common failure item many years later which was slightly leaky.


Many electronic devices will have a common problem. It may take a while to
find it,but once found, the first thing to look for.

I worked for a large company and we had a new building built and equipment
installed. All was fine for a while, the some heaters for the process got
where they would not come on if cut off. I was the first one to get a call
about this. Took about 2 or 3 hours to troubleshoot this as it was the
first time anyone had worked on it. Found a bad plug in time delay relay
was bad. After that a simple one point voltage check would usually tell the
relay was bad. Next time it only took seconds to change out the relay and
was usually done any time they would not come on. 99.9% of the time that
was the problem. As that place operated 24 hours a day, the peopel in
production was told about it and told the electrician that showed up to
change it out if they did not know what the problem might be. Saved lots of
late night phone calls.

On Friday, December 4, 2015 at 1:53:47 PM UTC-5, Ralph Mowery wrote:
"Chuck" wrote in in sci.electronics.repair in message
...
The receiver tech was flummoxed by one of those large 1970s Pioneer
receivers. It had a problem none of us had seen before and we were a
high volume audio chain. There was slight audio distortion on both
channels, only on FM. We all worked commission only so I was the only
one to volunteer to help him out. To cut to the chase, the receiver
had an over designed mute circuit that was 3 or 4 stages deep, At the
deepest stage there was one of the Sanyo electrolytics that became a
common failure item many years later which was slightly leaky.

Many electronic devices will have a common problem. It may take a while to
find it,but once found, the first thing to look for.

Most of them have microchips (that you can't open up and repair). And they have software and wireless or hard wired connections to larger facilities elsewhere where techs can come in and review the software.

Many problems seem to be caused from malware or spyware (maybe some even from the government or other places) that intentionally interferes with the intended software provided by the company on the package's label.

I worked for a large company and we had a new building built and
equipment installed.

Right now, I'm not even working. I'm just sitting around looking at space cartoons and video games.

Chuck wrote:
On Thu, 3 Dec 2015 06:34:55 -0600, "Mark Zacharias"
wrote:

OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.
The receiver tech was flummoxed by one of those large 1970s Pioneer
receivers. It had a problem none of us had seen before and we were a
high volume audio chain. There was slight audio distortion on both
channels, only on FM. We all worked commission only so I was the only
one to volunteer to help him out. To cut to the chase, the receiver
had an over designed mute circuit that was 3 or 4 stages deep, At the
deepest stage there was one of the Sanyo electrolytics that became a
common failure item many years later which was slightly leaky.

I've got another one. In the early 80s there were these 19" Hitachi
tvs that ghosted. It looked exactly like a bad delay line. By that
time I ran the TV service department for the same company. We had
just switched over to the big box store concept and I was inundated
with broken tvs. Out of desperation, I switched out the CRT and the
ghosting disappeared. We sold 1000s of these sets and I saw the
problem 3 more times.

And another. Kenwood sold these Funai made cd changers that never
worked properly. All of them would come back with skipping or not
playing discs problems. Kenwood came out with 3 or 4 mods, none which
worked. Sometimes they would work for months before they came back.
Somehow I found out if the mechanism retaining springs were stretched
so the mechanism didn't sag at all, the problem disappeared. Called
up Kenwood and they put out a mod kit that included strong springs
which also didn't allow any downward movement of the mechanism.

Was that the type with the CD cartridge, like a trunked automotive unit?
Those things were all such garbage.

On Mon, 7 Dec 2015 17:21:35 +0000 (UTC), Cydrome Leader
wrote:

Chuck wrote:
On Thu, 3 Dec 2015 06:34:55 -0600, "Mark Zacharias"
wrote:

OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.
The receiver tech was flummoxed by one of those large 1970s Pioneer
receivers. It had a problem none of us had seen before and we were a
high volume audio chain. There was slight audio distortion on both
channels, only on FM. We all worked commission only so I was the only
one to volunteer to help him out. To cut to the chase, the receiver
had an over designed mute circuit that was 3 or 4 stages deep, At the
deepest stage there was one of the Sanyo electrolytics that became a
common failure item many years later which was slightly leaky.

I've got another one. In the early 80s there were these 19" Hitachi
tvs that ghosted. It looked exactly like a bad delay line. By that
time I ran the TV service department for the same company. We had
just switched over to the big box store concept and I was inundated
with broken tvs. Out of desperation, I switched out the CRT and the
ghosting disappeared. We sold 1000s of these sets and I saw the
problem 3 more times.

And another. Kenwood sold these Funai made cd changers that never
worked properly. All of them would come back with skipping or not
playing discs problems. Kenwood came out with 3 or 4 mods, none which
worked. Sometimes they would work for months before they came back.
Somehow I found out if the mechanism retaining springs were stretched
so the mechanism didn't sag at all, the problem disappeared. Called
up Kenwood and they put out a mod kit that included strong springs
which also didn't allow any downward movement of the mechanism.

Was that the type with the CD cartridge, like a trunked automotive unit?
Those things were all such garbage.
No. It was a 5 disc carousel. Kenwood didn't have a design in the
pipeline so they outsourced it.

---
This email has been checked for viruses by Avast antivirus software.
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Chuck wrote:
On Mon, 7 Dec 2015 17:21:35 +0000 (UTC), Cydrome Leader
wrote:

Chuck wrote:
On Thu, 3 Dec 2015 06:34:55 -0600, "Mark Zacharias"
wrote:

OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.
The receiver tech was flummoxed by one of those large 1970s Pioneer
receivers. It had a problem none of us had seen before and we were a
high volume audio chain. There was slight audio distortion on both
channels, only on FM. We all worked commission only so I was the only
one to volunteer to help him out. To cut to the chase, the receiver
had an over designed mute circuit that was 3 or 4 stages deep, At the
deepest stage there was one of the Sanyo electrolytics that became a
common failure item many years later which was slightly leaky.

I've got another one. In the early 80s there were these 19" Hitachi
tvs that ghosted. It looked exactly like a bad delay line. By that
time I ran the TV service department for the same company. We had
just switched over to the big box store concept and I was inundated
with broken tvs. Out of desperation, I switched out the CRT and the
ghosting disappeared. We sold 1000s of these sets and I saw the
problem 3 more times.

And another. Kenwood sold these Funai made cd changers that never
worked properly. All of them would come back with skipping or not
playing discs problems. Kenwood came out with 3 or 4 mods, none which
worked. Sometimes they would work for months before they came back.
Somehow I found out if the mechanism retaining springs were stretched
so the mechanism didn't sag at all, the problem disappeared. Called
up Kenwood and they put out a mod kit that included strong springs
which also didn't allow any downward movement of the mechanism.

Was that the type with the CD cartridge, like a trunked automotive unit?
Those things were all such garbage.
No. It was a 5 disc carousel. Kenwood didn't have a design in the
pipeline so they outsourced it.

Sort of sad somebody messed up a carousel. The cartridge based changers
were infuriating.

Anything that requires extensive soldering and screwing around with that
medical type tape to open up, like portable tape/CD players and now
cameras suck too.

On Thursday, December 3, 2015 at 7:34:56 AM UTC-5, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

The one pops to mind took couple of years off my life. It was an old Hitachi built RCA projection TV (circa 1981) that had blown fuses in the power supply, but nothing showed a short resistance wise. I replaced the fuses and it powered up, only the geometry didn't look right. When I went to connect the cable back on to it to see exactly what the picture was like a blinding flash and arc appeared at the RF connector and it blew the fuses again. Working pretty much on my stomach in a cramped house, I traced a hot side/cold side short all the way back to the end of the line, which was a leaky deflection yoke (vert winding to horiz winding). It seems the horiz winding was on the hot side of the chassis and the vert winding was on the cold side. How it didn't blow the vert IC or horiz deflection output is a mystery.

On 12/3/2015 6:34 AM, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc
these days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in
the past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you
caught that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

In the late 80s early 90's I worked on VCR's. The Fisher FVH 906,
had a tuner that went defective, no schematic, a replacement part only.
That's ok under warranty, but after that, the part cost was to high to
get a repair ok. So one day, I decided to see if I could find out what
the cause of the failure was. I started spraying parts with freeze mist
and found when I hit a 1uf 35V cap the picture came back. I made a lot
of repairs, replacing that same cap on a whole bunch of tuners.
I'd do the same thing every time, dribble 2 or 3 drops of freeze mist
on the cap and the picture came in.

I had a customer bring in a remote for repair, it checked out fine.
He took it home and called saying it didn't work. I talked to him a bit
and found he had just install new CFL lights. I suggested he shield that
light and try it. It worked, I had just read about that in a trade
magazine two days previous.
Mikek

I got in early on the VCR curve, they were expensive, commanding high
service rates, then when prices dropped we had a high volume of repairs,
rode it down until the price was close to $200, then I moved to Florida.
A year later the tech that took my place said he came in a couple days
a week to repair the few that came in. I repaired a little over 11,000
vcr's in ten years, it was a good time.

On Fri, 4 Dec 2015 14:28:24 -0600, amdx wrote:

On 12/3/2015 6:34 AM, Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc
these days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in
the past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you
caught that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

In the late 80s early 90's I worked on VCR's. The Fisher FVH 906,
had a tuner that went defective, no schematic, a replacement part only.
That's ok under warranty, but after that, the part cost was to high to
get a repair ok. So one day, I decided to see if I could find out what
the cause of the failure was. I started spraying parts with freeze mist
and found when I hit a 1uf 35V cap the picture came back. I made a lot
of repairs, replacing that same cap on a whole bunch of tuners.
I'd do the same thing every time, dribble 2 or 3 drops of freeze mist
on the cap and the picture came in.

I had a customer bring in a remote for repair, it checked out fine.
He took it home and called saying it didn't work. I talked to him a bit
and found he had just install new CFL lights. I suggested he shield that
light and try it. It worked, I had just read about that in a trade
magazine two days previous.
Mikek

I got in early on the VCR curve, they were expensive, commanding high
service rates, then when prices dropped we had a high volume of repairs,
rode it down until the price was close to $200, then I moved to Florida.
A year later the tech that took my place said he came in a couple days
a week to repair the few that came in. I repaired a little over 11,000
vcr's in ten years, it was a good time.


In a similar vein to your remote story, we sold an $1800 Tandberg
cassette deck that came to the shop over and over again for not
responding to the transport keys. In the shop it always worked
perfectly. I decided to go to the customer's house after work to see
what the problem was. At his house, the keys didn't work. I spotted
a light dimmer on the wall. Turning it off and the deck worked
perfectly.

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In article ,
says...

In a similar vein to your remote story, we sold an $1800 Tandberg
cassette deck that came to the shop over and over again for not
responding to the transport keys. In the shop it always worked
perfectly. I decided to go to the customer's house after work to see
what the problem was. At his house, the keys didn't work. I spotted
a light dimmer on the wall. Turning it off and the deck worked
perfectly.

---
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https://www.avast.com/antivirus



While I was in a neighborhood visiting a nice looking girl, a friend of
hers ask if I could go over to their place and see why their portable
color TV near the door had messed up colors they could not remove.

I really didn't want to go and told them it would be a minimum of $20
bucks just to walk in, they accepted.

So I walked in and didn't even bother to turn the TV on. I reached up
on top of the TV set and removed the 9x6 Triaxal Speaker with a large
magnet on it, sitting there for what ever reason, I have no idea why.

I held my hand out for the money! They asked aren't you going to even
turn it on? I said, you can do that, they did and could not believe what
they saw. I took the money and said, have a good day now..

Jamie

Chuck wrote:



In a similar vein to your remote story, we sold an $1800 Tandberg
cassette deck that came to the shop over and over again for not
responding to the transport keys. In the shop it always worked
perfectly. I decided to go to the customer's house after work to see
what the problem was. At his house, the keys didn't work. I spotted
a light dimmer on the wall. Turning it off and the deck worked
perfectly.


** Need more explanation for that one.


..... Phil

On Sat, 5 Dec 2015 18:52:34 -0800 (PST), Phil Allison
wrote:

Chuck wrote:



In a similar vein to your remote story, we sold an $1800 Tandberg
cassette deck that came to the shop over and over again for not
responding to the transport keys. In the shop it always worked
perfectly. I decided to go to the customer's house after work to see
what the problem was. At his house, the keys didn't work. I spotted
a light dimmer on the wall. Turning it off and the deck worked
perfectly.


** Need more explanation for that one.


.... Phil
The light dimmer was putting an enormous amount of hash on the mains;
somehow it was getting into the microprocessor circuitry. I had seen
this before on much cheaper items so I had a hunch that this was the
problem.

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I almost want to say it was a fault, but it may have been the design. Really, when you talk old stuff, some things just did not exist back then. Things that cause more interference.

When working on older equipment, much older, I had to learn not to expect too much.

In that case with the Tandberg I would have gotten some line filtering. they make those all put together units you can put right at the AC input, light enough so you can cut the cord even and just glue them about anywhere, just make sure they are as close to the AC inlet as possible.

To figure it all out we woukld need the print for that Tandberg. I remember working on one R2R deck that had no microprocessor. It was all gates and comparators and all that. I think it was a 9200 ??? So that one probably would have been alright, no keyboard scanning or any of that, just a bunch of switches and flipflops and gates. and then the solenoid and relay drivers, oh and the current drivers for the eddy current motors.

Simple, I liked it. I fixed it. It got sold. It got damaged in shipping. We got ****ed. I wish I would have kept it but really, I have no tapes.

Chuck wrote:




The light dimmer was putting an enormous amount of hash on the mains;
somehow it was getting into the microprocessor circuitry. I had seen
this before on much cheaper items so I had a hunch that this was the
problem.



** Wall dimmers put large voltage spikes on the wiring going to the lamp/s concerned - two spikes per cycle at up to the peak AC voltage. This radiates as buzzing noise across the audio and also AM radio bands.

Well shielded, low impedance gear is not affected but anything high impedance and not well shielded picks it up. Electric guitars and some keyboards are particularly susceptible.

Seems your Tandberg was too and that is **** poor design.


..... Phil

Chuck wrote:
In a similar vein to your remote story, we sold an $1800 Tandberg
cassette deck that came to the shop over and over again for not
responding to the transport keys. In the shop it always worked
perfectly. I decided to go to the customer's house after work to see
what the problem was. At his house, the keys didn't work. I spotted
a light dimmer on the wall. Turning it off and the deck worked
perfectly.


I have a SABA music system (radio + cassette + turntable + audio in/out plugs + remote control), time ago I had it connected to a desktop PC to play music from the PC. One day the printer attached to the same PC was taken out for repair due to clogged heads.

The next day I found the SABA turned on with the MUTE activated (the radio was selected so the FM display etc was all lit, but no sound). Since I never used to use the MUTE button and I was the only one at home to use that thing I was quite surprised. I unmuted it and turned it off, all appeared to work correctly. The same day in the evening the same again, that made it obvious it was not me. In the next few days the same kept happening at random times but never when I was there, and because it would turn on with the mute set I could not hear when it happened.

Finally one day it was off, I went to the kitchen and when I came back it was on and muted again, so I guessed a relation had to exist. Turned it off and went to the kitchen again - no joy. Repeated a few times and surprise - again on and muted. Some more experiments revealed that switching off the kitchen light sometimes would cause the SABA to turn on and activate the mute at the same time.

The kitchen light consists of two 36W fluorescent tubes, apparently the inductive kick at turn off found its way into the SABA digital controls. They were two rooms apart, so not exactly next to the kitchen switch or lights. The issue did not reoccur after I plugged the printer back.

Jeroni Paul wrote:
Chuck wrote:
In a similar vein to your remote story, we sold an $1800 Tandberg
cassette deck that came to the shop over and over again for not
responding to the transport keys. In the shop it always worked
perfectly. I decided to go to the customer's house after work to see
what the problem was. At his house, the keys didn't work. I spotted
a light dimmer on the wall. Turning it off and the deck worked
perfectly.


I have a SABA music system (radio + cassette + turntable + audio in/out plugs + remote control), time ago I had it connected to a desktop PC to play music from the PC. One day the printer attached to the same PC was taken out for repair due to clogged heads.

The next day I found the SABA turned on with the MUTE activated (the radio was selected so the FM display etc was all lit, but no sound). Since I never used to use the MUTE button and I was the only one at home to use that thing I was quite surprised. I unmuted it and turned it off, all appeared to work correctly. The same day in the evening the same again, that made it obvious it was not me. In the next few days the same kept happening at random times but never when I was there, and because it would turn on with the mute set I could not hear when it happened.

Finally one day it was off, I went to the kitchen and when I came back it was on and muted again, so I guessed a relation had to exist. Turned it off and went to the kitchen again - no joy. Repeated a few times and surprise - again on and muted. Some more experiments revealed that switching off the kitchen light sometimes would cause the SABA to turn on and activate the mute at the same time.

The kitchen light consists of two 36W fluorescent tubes, apparently the inductive kick at turn off found its way into the SABA digital controls. They were two rooms apart, so not exactly next to the kitchen switch or lights. The issue did not reoccur after I plugged the printer back.

Ha!

Was noise filtering on the always on printer was somehow supressing the
interference?

Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in
areas like repairing audio components, amps, receivers, power
supplies, etc these days.

I "tune in" here almost daily and rarely find anything of interest to
me.
Maybe we could share some "war stories" of cool repairs we have done
in the past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you
caught that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.

One of my first chances to stick my chest out and strut was shortly after I
checked aboard my first duty ship during my stint in the Navy in mid-1964.
Barely 20 years old, I was assigned to overhaul & repair of UHF shipboard
radio transmitters.

The ship had a small calibration lab, which was staffed by a PO1, a PO2s and
a couple PO3s (POs are Petty Officers... enlisted men) who had all been to
the elite Air Force PMEL calibration school in Colorado. One day, after all
the cal lab techs had a shot at it and several of the other bench techs had
also been called in to try fixing it,, I was called in to take a shot at
repairing a new HP 524D 10MC digital counter from another ship. It just
wouldn't show any indication of trying to count... all the displays just
sat at zero no matter what the input signal looked like.

I sat down and took a look at the schematic, hooked a scope probe to the
output of the gate tube, a 6AL5. No pulses. Hooked the probe to the gate
input to the gate tube. Good gate pulses. Hooked the probe to the signal
input of the gate tube. Good squared pulses that followed the frequency of
the input signal.
I asked for a 6AL5 tube, plugged it in, and Voila! everything came to life.

Made me feel kinda good that it only took me about 10 minutes to fix what
had stumped 9 or 10 good techs for several days. From that day until now, I
have had an affinity for test instruments, especially those used for time &
frequency measurement.

Dave M

Mark Zacharias wrote:


OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?


** Ok, here is a wacky one:

I once had a customer who rented out DJ systems: turntable & mixer consoles, stereo amps and speakers. DJs back then owned a collection of LPs and generally rented audio gear on a daily basis.

So I got this TT console with the complaint while it started off OK, it was losing volume & changing tone after a while becoming duller and duller until full treble was needed to correct it.

The story sounded dubious, but I checked out the mixer thoroughly using hot air and an all day soak test - result negative, it worked fine all the time.

Handed it back to the hire business guy and a week later it was returned with the SAME complaint plus some hostility that I had clearly not fixed it. Naturally it passed all tests again.

I had a chat with the hire guy and he agreed to use the console himself at a gig and of course it worked fine all night. Next time it went out on hire, he got the same complaint from the same DJ - who was by now ropable that nothing had been done about the problem.

So my hire guy paid a visit to the venue where the gear was being used, his first. When he walked in, he was nearly deafened by the volume and the sound was absurdly shrill. On approaching the DJ and noticing that volume and treble controls were all maxed out - he was told:

" See what I mean ??

Sounds **** weak and there's no treble."



..... Phil

Chances are he'll never hear his grandkids cry.

On Thu, 03 Dec 2015 06:34:55 -0600, Mark Zacharias wrote:

Maybe we could share some "war stories" of cool repairs we have done
in the past.

Somewhere in the eighties we installed a custom-built control system in
a 24/7 assembly line for SIL ceramic hybrid circuits.
Subcontractor of subcontractor job.

One night I was called in for an unexpected stop.
Inside the plant I was 'greeted' by the crowd of tech support people and
blaming managers gathered around our equipment.
On my way to the control system I came across one of the typical mushroom
emergency stops along the production line.
By habit I twisted the knob and felt the release spring.
I worked my way to the control panel and engaged the start.
Within seconds the crowd silenced and fled the scene: the line was up.

We were never again called in.

"c4urs11" wrote in message
...
On Thu, 03 Dec 2015 06:34:55 -0600, Mark Zacharias wrote:

Maybe we could share some "war stories" of cool repairs we have done
in the past.

Somewhere in the eighties we installed a custom-built control system in
a 24/7 assembly line for SIL ceramic hybrid circuits.
Subcontractor of subcontractor job.

One night I was called in for an unexpected stop.
Inside the plant I was 'greeted' by the crowd of tech support people and
blaming managers gathered around our equipment.
On my way to the control system I came across one of the typical mushroom
emergency stops along the production line.
By habit I twisted the knob and felt the release spring.
I worked my way to the control panel and engaged the start.
Within seconds the crowd silenced and fled the scene: the line was up.

We were never again called in.

About 1981 I was still in tech school and not even really a technician yet.

(I was SO green).

Third semester, servicing phase. There was an old GE tube chassis color set
with intermittent color sync. It was a "re-do" which the prior class had
failed to fix correctly.

I got to the burst gate amp and saw there was a much smaller signal at the
grid than called for.

Also, there was a neon lamp in the grid circuit which was supposed to drop
75 or so volts and the drop was much higher than expected, plus the lamp
glowed somewhat faintly at it's base instead of lighting fully.

I couldn't get the instructor to order a miserable 75 cent neon lamp. He
kept me running around checking this cap or this resistor, etc.

Finally I went around him to another instructor, explained my logic and got
the lamp ordered.

Fixed the tv. My instructor never really forgave me for that.


Mark Z.

Things that are second nature to us now were "learning experiences" back
then, yes?

At my first job as a tech, about the second piece I ever worked on was a
Pioneer SX-828.

Yup - the infamous "blue Sanyo cap" scenario.

Except I had never heard of that and had no tech support or even a more
experienced tech along side me.

I was totally on my own, as I usually was during the first 15 or 20 years of
my career.

Symptom: one channel gone, just a low hiss. Preamp issue.

Tracing signal - got it, don't got it, and so on.

In the tone amp, DC voltage low at collector of one transistor.

1.5uF Sanyo coupling cap to base was leaky, driving that stage into
saturation.

Felt really good about that one.


Mark Z.

On 12/5/2015 6:52 AM, Mark Zacharias wrote:
Things that are second nature to us now were "learning experiences" back
then, yes?

At my first job as a tech, about the second piece I ever worked on was a
Pioneer SX-828.

Yup - the infamous "blue Sanyo cap" scenario.

Except I had never heard of that and had no tech support or even a more
experienced tech along side me.

I was totally on my own, as I usually was during the first 15 or 20
years of my career.

Symptom: one channel gone, just a low hiss. Preamp issue.

Tracing signal - got it, don't got it, and so on.

In the tone amp, DC voltage low at collector of one transistor.

1.5uF Sanyo coupling cap to base was leaky, driving that stage into
saturation.

Felt really good about that one.


Mark Z.

I had an SX-828, bought it sometime in the early 70s.
Been so many years, I don't recall the problem, but
I tossed it about two years ago, just too much stuff.

Mikek