I was given this TV today to try and repair. I know the power
supplies on this model have been a big problem, but before I buy a
replacement I wanted to run the symptoms by you guys.

It was working for a while on tuner mode and then got stuck on one of
the inputs and would not allow for it to be changed. It was used like
this for a few weeks and then got stuck running in the test pattern.
Every 5 seconds or so a different color screen would show up and then
sometimes the full color bar test pattern. I took the back off and
took the following measurements at power supply connectors both when
the unit is on and when it is in standby.

CN102
On (Standby)
1 - 12.09 (0)
2 - 12.09 (0)
3 - GND
4 - GND
5 - GND
6 - GND
7 - 5.11 (5.11)
8 - 5.11 (5.11)
9 - 5.11 (5.11)
10 - 3.47 (.062)
11 - 3.57 (.627)
12 - 4.87 (.006)

CN101
On (Standby)
1 - GND
2 - GND
3 - GND
4 - GND
5 - 23.75 (0)
6 - 23.75 (0)
7 - 23.75 (0)
8 - 23.75 (0)
9 - 3.57 (.627)
10 - 4.87 (.006)

I removed the power supply completely and can see no evidence of
faulty capacitors and the voltages all seem to be in range. My only
concerns are the On/Standby voltage being 3.47V, although I don't have
the schematics so I am not sure what it should be. I might have
expected something closer to 5V. If that is the expected value I may
try to strap an external 5V supply on and run as a test.

At one point using the top switches I was able to change the input
mode to VGA, and I am now driving it with a netbook and it gives me a
beautiful picture, I just am unable to change it to anything else. An
the OSD window for "Main:" stays on the screen. The voltages at P701
(top side switch board) are as follows:
On (Standby)
Orange - 0 (3.77)
Blue - 3.74 (3.77)
Red - 3.74 (3.77)
Green - 3.74 (3.77)
Yellow - 3.74 (3.77)
Black - 0 (0)
Brown - 3.74 (3.77)

Has anyone seen similar symptoms with their set? I have no problem
dropping money on the replacement supply, I just want some confidence
the problem isn't with the motherboard before I invest anything more
than my time. No post that I could find described symptoms similar to
what I am seeing. Also does anyone have the schematics or repair
manual for this set? If so please send me copies via email.

All help is appreciated.

Stephen

On Nov 20, 8:43*pm, playedataritoday
wrote:
I was given this TV today to try and repair. *I know the power
supplies on this model have been a big problem, but before I buy a
replacement I wanted to run the symptoms by you guys.

It was working for a while on tuner mode and then got stuck on one of
the inputs and would not allow for it to be changed. *It was used like
this for a few weeks and then got stuck running in the test pattern.
Every 5 seconds or so a different color screen would show up and then
sometimes the full color bar test pattern. *I took the back off and
took the following measurements at power supply connectors both when
the unit is on and when it is in standby.

CN102
* * * On *(Standby)
1 - 12.09 (0)
2 - 12.09 (0)
3 - GND
4 - GND
5 - GND
6 - GND
7 - 5.11 (5.11)
8 - 5.11 (5.11)
9 - 5.11 (5.11)
10 - 3.47 (.062)
11 - 3.57 (.627)
12 - 4.87 (.006)

CN101
* * *On (Standby)
1 - GND
2 - GND
3 - GND
4 - GND
5 - 23.75 (0)
6 - 23.75 (0)
7 - 23.75 (0)
8 - 23.75 (0)
9 - 3.57 (.627)
10 - 4.87 (.006)

I removed the power supply completely and can see no evidence of
faulty capacitors and the voltages all seem to be in range. *My only
concerns are the On/Standby voltage being 3.47V, although I don't have
the schematics so I am not sure what it should be. *I might have
expected something closer to 5V. *If that is the expected value I may
try to strap an external 5V supply on and run as a test.

At one point using the top switches I was able to change the input
mode to VGA, and I am now driving it with a netbook and it gives me a
beautiful picture, I just am unable to change it to anything else. An
the OSD window for "Main:" stays on the screen. *The voltages at P701
(top side switch board) are as follows:
* * * * *On (Standby)
Orange - 0 (3.77)
Blue - 3.74 (3.77)
Red - 3.74 (3.77)
Green - 3.74 (3.77)
Yellow - 3.74 (3.77)
Black - 0 (0)
Brown - 3.74 (3.77)

Has anyone seen similar symptoms with their set? *I have no problem
dropping money on the replacement supply, I just want some confidence
the problem isn't with the motherboard before I invest anything more
than my time. *No post that I could find described symptoms similar to
what I am seeing. *Also does anyone have the schematics or repair
manual for this set? *If so please send me copies via email.

All help is appreciated.

Stephen


I bet you're wrong on the capacitor issue. I replace so many caps at
work I'm the 'cap guy' that gets most stuff working again for next to
nothing. Hints: If a cap looks bad it probably is but if it looks OK
it may actually be bad. Look for a brown 'mist' around a capacitor.
Those must be removed, the acid mist cleaned off a a new cap
installed. It will often have a 'fishy' odor. Without the mist it may
still be bad and look fine. The high voltage (300-500Volt) caps rarely
fail. The 22 -100uF low voltage caps frequently fail and the worst are
surface mount 'lytics. I replace LOTS of those. Many times a 'lytic
will have a ceramic in parallel. This might look OK on the tester
(Cheapest I know of is the MAT Electronics MUL-3333 at $50) as the
meter is seeing the ceramic but the 'lytic is bad. Only way to verify
is to remove the cap and test it by itself. It will read better while
its warm and as it cools will get worse. Rule of thumb: if there are a
lot of the same value and some are bad, replace them all. Look for
highest ripple current in the Digikey (and others) catalog. Often it
will be a Panasonic FM or FC or Nichicon HL HM HN, HZ for through
hole. I like Panasonic FK or FP for surface mount.

G²

I don't know anything related to this TV, but bad capacitors which show
visible signs of defects are generally a result of only one type of fault
(internal heating).

There are numerous other faults/states of decay, but ESR is most often
mentioned.

ESR testing is a very important/critical parameter to test for particularly
in the high frequency and ripple conditions of SMPS, but passing an ESR test
alone, will not prove that an electrolytic capacitor is in good condition
(without faults).

There are numerous websites with free schematics available, and many of them
are routinely mentioned here in the SER newsgroup.
You might get lucky finding a schematic or an entire service manual.

Your listed measurements do show +5V in standby, so your question is a bit
confusing. I don't know if the PSU would/should provide other voltages in
standby or with the power on.

--
Cheers,
WB
..............

"playedataritoday" wrote in message
...
I was given this TV today to try and repair. I know the power
supplies on this model have been a big problem, but before I buy a
replacement I wanted to run the symptoms by you guys.

It was working for a while on tuner mode and then got stuck on one of
the inputs and would not allow for it to be changed. It was used like
this for a few weeks and then got stuck running in the test pattern.
Every 5 seconds or so a different color screen would show up and then
sometimes the full color bar test pattern. I took the back off and
took the following measurements at power supply connectors both when
the unit is on and when it is in standby.

CN102
On (Standby)
1 - 12.09 (0)
2 - 12.09 (0)
3 - GND
4 - GND
5 - GND
6 - GND
7 - 5.11 (5.11)
8 - 5.11 (5.11)
9 - 5.11 (5.11)
10 - 3.47 (.062)
11 - 3.57 (.627)
12 - 4.87 (.006)

CN101
On (Standby)
1 - GND
2 - GND
3 - GND
4 - GND
5 - 23.75 (0)
6 - 23.75 (0)
7 - 23.75 (0)
8 - 23.75 (0)
9 - 3.57 (.627)
10 - 4.87 (.006)

I removed the power supply completely and can see no evidence of
faulty capacitors and the voltages all seem to be in range. My only
concerns are the On/Standby voltage being 3.47V, although I don't have
the schematics so I am not sure what it should be. I might have
expected something closer to 5V. If that is the expected value I may
try to strap an external 5V supply on and run as a test.

At one point using the top switches I was able to change the input
mode to VGA, and I am now driving it with a netbook and it gives me a
beautiful picture, I just am unable to change it to anything else. An
the OSD window for "Main:" stays on the screen. The voltages at P701
(top side switch board) are as follows:
On (Standby)
Orange - 0 (3.77)
Blue - 3.74 (3.77)
Red - 3.74 (3.77)
Green - 3.74 (3.77)
Yellow - 3.74 (3.77)
Black - 0 (0)
Brown - 3.74 (3.77)

Has anyone seen similar symptoms with their set? I have no problem
dropping money on the replacement supply, I just want some confidence
the problem isn't with the motherboard before I invest anything more
than my time. No post that I could find described symptoms similar to
what I am seeing. Also does anyone have the schematics or repair
manual for this set? If so please send me copies via email.

All help is appreciated.

Stephen

Wild_Bill wrote in message
...
I don't know anything related to this TV, but bad capacitors which show
visible signs of defects are generally a result of only one type of fault
(internal heating).



Does anyone routinely add a small 12V fan/baffles/ducting in such
circumstances? as well as changing caps

Any time I'm inside a case, I try to move electrolytics away from power
resistors, heatsinks and other sources of heat, just for S&G.. it may help.

Because electrolytics are heated internally in most SMPS (secondary side)
applications, I wouldn't think extra venting or supplemental cooling with a
tiny fan would add much toward the caps' lifetimes.. they're just destined
to fail.

When a fan is near a power transformer, for example, it may lower the
surface temperature somewhat, which in turn "draws" more heat from the core,
but the core remains substantially hotter than the outer surface.

Electrolytic caps are smaller, and aluminum outer shells, but there is often
a (heat) insulating/blocking air layer between the can and the actual
layered materials in the center.
Air is an excellent heat insulator, so cooling the can wouldn't so much have
a chilling effect on the core, IMO.

Perhaps cooling the copper traces on the PCB would be a more effective
approach.. the internal aluminum foil ends are secured/in contact with the
cap's copper leads, which are in turn soldered to the PCB foil, and copper
is a very good conductor of heat, so the heat transfer could be somewhat
significant.
Definite maybe.

Unrelated drivel:
I recently had a small accident with an RCA/China VR5220-A pocket digital
voice recorder, where it slipped into the sink while the water was on, so I
opened it to get all traces of the water out.
I was just a little surprised to see 105 C rated electrolytics inside (all
of 'em, and quite a few, too)

--
Cheers,
WB
..............


"N_Cook" wrote in message
...
Wild_Bill wrote in message
...
I don't know anything related to this TV, but bad capacitors which show
visible signs of defects are generally a result of only one type of fault
(internal heating).



Does anyone routinely add a small 12V fan/baffles/ducting in such
circumstances? as well as changing caps

Because electrolytics are heated internally in most SMPS
(secondary side) applications, I wouldn't think extra venting
or supplemental cooling with a tiny fan would add much
toward the caps' lifetimes... they're just destined to fail.

One tends to think of electrolytics as /inherently/ failure-prone. But has
this always been true? Or are you thinking just of switching and/or "tightly
packed" power supplies?

I've been buying electronic equipment, used and (mostly) new for 45 years,
and very, very few items have had bad 'lytics, or 'lytics that turned bad. I
remember a used KLH compact stereo that needed new caps, and two JVC hall
synthesizers that needed replacement PS caps. (The latter had been built
with known-bad caps.) And that's about it.

I owned several KLH Model Eight table radios (circa 1960), and none ever
needed a new 'lytic.

On a vaguely related note... It's nice to see that more and more products
are coming with switching wall warts.


I recently had a small accident with an RCA/China VR5220-A
pocket digital voice recorder, where it slipped into the sink while
the water was on, so I opened it to get all traces of the water out.
I was just a little surprised to see 105 C rated electrolytics inside
(all of 'em, and quite a few, too).

Perhaps the manufacturer used premium caps in all its products, simply to
avoid multiple inventory.

William Sommerwerck wrote:

Because electrolytics are heated internally in most SMPS
(secondary side) applications, I wouldn't think extra venting
or supplemental cooling with a tiny fan would add much
toward the caps' lifetimes... they're just destined to fail.

One tends to think of electrolytics as /inherently/ failure-prone. But has
this always been true? Or are you thinking just of switching and/or "tightly
packed" power supplies?

I've been buying electronic equipment, used and (mostly) new for 45 years,
and very, very few items have had bad 'lytics, or 'lytics that turned bad. I
remember a used KLH compact stereo that needed new caps, and two JVC hall
synthesizers that needed replacement PS caps. (The latter had been built
with known-bad caps.) And that's about it.


Most of that equipment had a better grade of electrolytics. The
imported stuff is crammed into tiny containers which can't disiapate
much heat. Low ESR caps in switching power supplies have to be very
close to both the recitifers, and the load, so they are in a hotspot,
which further reduces the reliability. Some CPUs draw over 100 A at
less than 2 Volts. If the CPU power supply was on a corner of the
motherboard, the voltage drop would waste a lot of power, and create
more waste heat.



I owned several KLH Model Eight table radios (circa 1960), and none ever
needed a new 'lytic.


Sprague, Mallory ore CDE electrolytics? Maybe Sangamo.


On a vaguely related note... It's nice to see that more and more products
are coming with switching wall warts.


Except when they radiate a lot of RF noise.


I recently had a small accident with an RCA/China VR5220-A
pocket digital voice recorder, where it slipped into the sink while
the water was on, so I opened it to get all traces of the water out.
I was just a little surprised to see 105 C rated electrolytics inside
(all of 'em, and quite a few, too).

Perhaps the manufacturer used premium caps in all its products, simply to
avoid multiple inventory.


Or they are cheap, no name Chinese fakes.


--
For the last time: I am not a mad scientist, I'm just a very ticked off
scientist!!!

The switch mode SMPS power supplies are running at high frequencies for
efficiency, and by design. The high frequency is vaguely similar to an
ultrasonic cleaner, or an ultrasonic muscle therapy unit.. if the muscle
therapy is set too high, or is allowed to sit on one spot, damage to the
muscle tissue can occur.

The electrolyte in the caps is going thru much the same treatment.. heated
by high freq and relatively high loads, internal heating results, and
electrolyte will likely be vented gradually until the cap eventually
avalanches into a rapid failure mode.

In addition to the severe duty they undergo, manufacturers want cheap PSUs,
and low quality caps are cheaper.

It's really a good feeling to have an old piece of equipment that still
operates fairly well, and hasn't been repaired.. or barely needed a minor
repair (dial lights).
I especially like to see a video display on an old TV or monitor.. it just
amuses me, and then I shake my head, thinking of today's equipment.
It's been a while since parents routinely gave their used still-working well
TV to the kids or grandkids when they buy a big new one.. but TVs were about
as durable as furniture. Many of them required 2 adults to move them, and
they used a lot of power.. I remember the last round-screen console color TV
I saw, was rated at 300 or 350W consumption. The power transformer in that
TV probably weighed as much as a 17" LCD monitor does now.

Capacitors that are subjected to 60Hz line frequency are less likely to be
operating on the edge of destruction. It seems that as long as there is a
small amount of moisture in the can, they function as intended.
Not only that, but capacitors of yesteryear were huge, and far less
susceptable to damage from moderate loads. Old aluminum can electrolytics
were often marked with nominal peak current ratings.

I would expect that you are correct regarding the common stocking of the 105
C rated caps found in a 3V device.

--
Cheers,
WB
..............


"William Sommerwerck" wrote in message
...

One tends to think of electrolytics as /inherently/ failure-prone. But has
this always been true? Or are you thinking just of switching and/or
"tightly
packed" power supplies?

I've been buying electronic equipment, used and (mostly) new for 45 years,
and very, very few items have had bad 'lytics, or 'lytics that turned bad.
I
remember a used KLH compact stereo that needed new caps, and two JVC hall
synthesizers that needed replacement PS caps. (The latter had been built
with known-bad caps.) And that's about it.

I owned several KLH Model Eight table radios (circa 1960), and none ever
needed a new 'lytic.

On a vaguely related note... It's nice to see that more and more products
are coming with switching wall warts.


Perhaps the manufacturer used premium caps in all its products, simply to
avoid multiple inventory.

In article ,
William Sommerwerck wrote:
One tends to think of electrolytics as /inherently/ failure-prone. But
has this always been true? Or are you thinking just of switching and/or
"tightly packed" power supplies?

I've been buying electronic equipment, used and (mostly) new for 45
years, and very, very few items have had bad 'lytics, or 'lytics that
turned bad. I remember a used KLH compact stereo that needed new caps,
and two JVC hall synthesizers that needed replacement PS caps. (The
latter had been built with known-bad caps.) And that's about it.

Think they always were a weak link if used in arduous conditions. Things
like WW2 and after military portable comms radios. Overhaul consisted of
replacing all the electrolytics regardless.

--
*See no evil, Hear no evil, Date no evil.

Dave Plowman London SW
To e-mail, change noise into sound.

Your listed measurements do show +5V in standby, so your question is a bit
confusing. I don't know if the PSU would/should provide other voltages in
standby or with the power on.

Actually the measurements I am concerned about we
CN102
On (Standby)
10 - 3.47 (.062)
11 - 3.57 (.627)
12 - 4.87 (.006)

I would have expected the values of these lines to be closer to 5V.
The more I read up on this TV, it might be a problem with Q7 and ZD4.
Does anybody have any actual experience with this TV?

"Dave Plowman (News)" wrote:

In article ,
William Sommerwerck wrote:
One tends to think of electrolytics as /inherently/ failure-prone. But
has this always been true? Or are you thinking just of switching and/or
"tightly packed" power supplies?

I've been buying electronic equipment, used and (mostly) new for 45
years, and very, very few items have had bad 'lytics, or 'lytics that
turned bad. I remember a used KLH compact stereo that needed new caps,
and two JVC hall synthesizers that needed replacement PS caps. (The
latter had been built with known-bad caps.) And that's about it.

Think they always were a weak link if used in arduous conditions. Things
like WW2 and after military portable comms radios. Overhaul consisted of
replacing all the electrolytics regardless.



Spare electrolytics were reformed at a set interval in the US
military. I've seen 30 year old Sprague electrolytic capacitors that
were still perfect.


--
For the last time: I am not a mad scientist, I'm just a very ticked off
scientist!!!

"playedataritoday" wrote in message
...
I was given this TV today to try and repair. I know the power
supplies on this model have been a big problem, but before I buy a
replacement I wanted to run the symptoms by you guys.

It was working for a while on tuner mode and then got stuck on one of
the inputs and would not allow for it to be changed. It was used like
this for a few weeks and then got stuck running in the test pattern.
Every 5 seconds or so a different color screen would show up and then
sometimes the full color bar test pattern. I took the back off and
took the following measurements at power supply connectors both when
the unit is on and when it is in standby.

CN102
On (Standby)
1 - 12.09 (0)
2 - 12.09 (0)
3 - GND
4 - GND
5 - GND
6 - GND
7 - 5.11 (5.11)
8 - 5.11 (5.11)
9 - 5.11 (5.11)
10 - 3.47 (.062)
11 - 3.57 (.627)
12 - 4.87 (.006)

CN101
On (Standby)
1 - GND
2 - GND
3 - GND
4 - GND
5 - 23.75 (0)
6 - 23.75 (0)
7 - 23.75 (0)
8 - 23.75 (0)
9 - 3.57 (.627)
10 - 4.87 (.006)

I removed the power supply completely and can see no evidence of
faulty capacitors and the voltages all seem to be in range. My only
concerns are the On/Standby voltage being 3.47V, although I don't have
the schematics so I am not sure what it should be. I might have
expected something closer to 5V. If that is the expected value I may
try to strap an external 5V supply on and run as a test.

At one point using the top switches I was able to change the input
mode to VGA, and I am now driving it with a netbook and it gives me a
beautiful picture, I just am unable to change it to anything else. An
the OSD window for "Main:" stays on the screen. The voltages at P701
(top side switch board) are as follows:
On (Standby)
Orange - 0 (3.77)
Blue - 3.74 (3.77)
Red - 3.74 (3.77)
Green - 3.74 (3.77)
Yellow - 3.74 (3.77)
Black - 0 (0)
Brown - 3.74 (3.77)

Has anyone seen similar symptoms with their set? I have no problem
dropping money on the replacement supply, I just want some confidence
the problem isn't with the motherboard before I invest anything more
than my time. No post that I could find described symptoms similar to
what I am seeing. Also does anyone have the schematics or repair
manual for this set? If so please send me copies via email.

All help is appreciated.

Stephen


The voltage that you see at 3.74 is almost certainly the 3.3v standby supply
for the system control micro. I would NOT under any circumstances, hit this
rail with 5v. Although it sounds a little high, such rails often are a few
decimals above the 3.3v nominal value. The 23.75v is the 24v nominal supply
for the backlight inverter. Other 12's and 5's are the general supplies for
the analogue and digital circuitry.

Whilst it is true that electrolytics do cause a lot of problems in
switchmode power supplies, I have never been an advocate of just blanket
changing them for the hell of it. It is easy - particularly if you are not
highly skilled with a soldering iron of the right power rating, and with the
right size and shape of tip, to create more problems than you think you are
fixing. By all means, suspect electrolytics - they can be responsible for
some bizarre fault symptoms, although I have to say that this one doesn't
'feel' like an electrolytic problem - but do the proper checks on them
first - that is initially, an ESR check, which in my experience, will find
over 90% of bad caps, followed by looking for hash on the rails with a
'scope. This will find any that have gone low value without their ESR
changing significantly (rare, but it does happen. Much more usually, the
other way round) without having to remove them from the board to check with
a capacitance meter.

Before going any further, I would also check that you haven't got any
problems with any of the user switches sticking or leaking, particularly if
this TV is used anywhere moist or greasy like a kitchen. I have a 'cheapo'
LCD in my kitchen, and from time to time, the volume 'UP' button gets leaky,
and the volume then goes up and up, until you rush over and switch off. When
it's doing it, a couple of buttons still work, but most are locked out. How
the micro responds to this type of fault condition, depends a lot on whether
it is a 'straight' xxx by yyy switch matrix connected to a pair of digital
ports, or a series switch - R - switch setup, connected to an ADC input on
the micro. With this type of arrangement, I have also had leaky decoupling
caps along the chain, causing the micro to sense erroneous 'button push'
conditions. Good luck with it. Try to use a structured and disciplined
approach to troubleshooting the problem, and try to avoid shotgunning
component groups, unless you are confident that you have one or more
problems among them, and are totally confident in your soldering abilities.

Arfa

JW wrote:

Michael A. Terrell wrote:

It says the input is DC coupled. You need AC coupling, or a very
wide adjustment of the vertical position to see just the ripple.

True, that would be best, but even DC coupled, looking across a filter cap
that would normally have 50VDC across it, it would be fairly easy to see 5
volts of ripple. Would probably be trivial to modify the scope or probe
and put a small ceramic cap inline.


A small ceramic capacitor? For a scope with an attached probe and no
publihed input impedance?


--
For the last time: I am not a mad scientist, I'm just a very ticked off
scientist!!!