I fired it up today and no joy. Took off all the covers/shields and tested
all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely on
it now. Any suggestions?

Thanks!

"Charles" wrote in message
...
I fired it up today and no joy. Took off all the covers/shields and
tested all the fuses and still no joy. Reseated all the connectors and
ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely
on it now. Any suggestions?

Thanks!

Is there a memory backup battery in it? Is it good?

On Nov 7, 7:18*pm, "Charles" wrote:
I fired it up today and no joy. * Took off all the covers/shields and tested
all the fuses and still no joy. *Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? *I need this generator for an important project but can't rely on
it now. *Any suggestions?

Thanks!

Bad switch contacts, did you check for any voltages after the pwer
switch?

On Wed, 7 Nov 2012 20:18:39 -0500, "Charles"
wrote:

I fired it up today and no joy. Took off all the covers/shields and tested
all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely on
it now. Any suggestions?

Power wiring, switch contacts, flakey fuse, corroded PCB contacts,
etc. However, it could also be bad power supply capacitors, which is
my best guess. Use an ESR tester to check the caps or just replace
them.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 11/7/2012 5:18 PM, Charles wrote:
I fired it up today and no joy. Took off all the covers/shields and
tested all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely
on it now. Any suggestions?

Thanks!
Assume the first thing you did was test it in another mainframe?
Or at least moved it to another socket in the same mainframe?
I also assume that you have something else in the mainframe so you
can rule out a bad power switch or corroded fuse holder or any
other common stuff.

The FG507 post-dates my tenure with TM500 engineering.
It's been 35 years and I'm OLD...so much of what I'm about to
say may be correct...maybe...YMMV.

The mainframe supplies unregulated DC.
~7V intended to be regulated to +5.
+/- 20ish intended to be regulated to +/-15V or so.
Because of the wide line voltage specs and cross loading,
it's difficult to get more than +/-15V regulated under worst
case conditions.

There are two floating transformer windings per hole. You can
get +/-20VDC if you're careful with the rectifier and regulator
design.

Each hole has one NPN and one PNP transistor allocated to it.
These are often used as pass transistors for power supply regulation.
I believe that all TM500 stuff of this era had linear regulated power
supplies.

A common failure is that the mainframe pass transistors come unsoldered
at the backplane board and become intermittent. Some plugins run them
hot, so the transistors themselves can become intermittent.

FG507 schematic doesn't seem to be available, but almost any TM500
signal generator from that era will have a similar power supply topology.
The tm503 manual has all the mainframe parts and pinouts.

"mike" wrote in message ...

On 11/7/2012 5:18 PM, Charles wrote:
I fired it up today and no joy. Took off all the covers/shields and
tested all the fuses and still no joy. Reseated all the connectors and
ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely
on it now. Any suggestions?

Thanks!

Thanks Mike. I tried it in every position in the mainframe. Also, other
plug-ins work.

I never turned it off and it is still working. I will leave it powered on
until this project is completed and then look for a new function generator.
Darn, I really liked the FG507.

"I never turned it off and it is still working. I will leave it powered on
until this project is completed and then look for a new function generator. "

You are SO looking at bad capacitors. If it stops working when you are done and you need it again, put it in the oven on keepwarm. Or change the capacitors of course.

J

On Thu, 8 Nov 2012 16:18:20 -0500 "Charles"
wrote in Message id: :



"mike" wrote in message ...

On 11/7/2012 5:18 PM, Charles wrote:
I fired it up today and no joy. Took off all the covers/shields and
tested all the fuses and still no joy. Reseated all the connectors and
ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely
on it now. Any suggestions?

Thanks!

Thanks Mike. I tried it in every position in the mainframe. Also, other
plug-ins work.

I never turned it off and it is still working. I will leave it powered on
until this project is completed and then look for a new function generator.
Darn, I really liked the FG507.

Manuals Plus claims to have a service manual.
http://www.manualsplus.com/catalog/p....php?sku=82316

You could also try asking on one of the Yahoo Tekscopes group.

On Fri, 09 Nov 2012 05:49:10 -0500, JW wrote:

Manuals Plus claims to have a service manual.
http://www.manualsplus.com/catalog/p....php?sku=82316
You could also try asking on one of the Yahoo Tekscopes group.

Also, eBay for $14.50:
http://www.ebay.com/itm/390187686761

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Fri, 09 Nov 2012 07:32:10 -0800 Jeff Liebermann
wrote in Message id: :

On Fri, 09 Nov 2012 05:49:10 -0500, JW wrote:

Manuals Plus claims to have a service manual.
http://www.manualsplus.com/catalog/p....php?sku=82316
You could also try asking on one of the Yahoo Tekscopes group.

Also, eBay for $14.50:
http://www.ebay.com/itm/390187686761

Huh. Yet Dave's webpage doesn't list it (I checked before posting the
above.)
http://artekmanuals.com/manuals

I'd email him and save a few bucks, that way you can also download - no
waiting for a CD.

"Jeff Liebermann" wrote in message
...
On Fri, 09 Nov 2012 05:49:10 -0500, JW wrote:

Manuals Plus claims to have a service manual.
http://www.manualsplus.com/catalog/p....php?sku=82316
You could also try asking on one of the Yahoo Tekscopes group.

Also, eBay for $14.50:
http://www.ebay.com/itm/390187686761

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Also, Qservice has it for download as a PDF for $7.49

http://www.qservice.tv/vpasp/shopexd.asp?id=269

Good quality scans.

On Fri, 09 Nov 2012 10:42:52 -0500 JW wrote in Message id:
:

On Fri, 09 Nov 2012 07:32:10 -0800 Jeff Liebermann
wrote in Message id: :

On Fri, 09 Nov 2012 05:49:10 -0500, JW wrote:

Manuals Plus claims to have a service manual.
http://www.manualsplus.com/catalog/p....php?sku=82316
You could also try asking on one of the Yahoo Tekscopes group.

Also, eBay for $14.50:
http://www.ebay.com/itm/390187686761

Huh. Yet Dave's webpage doesn't list it (I checked before posting the
above.)
http://artekmanuals.com/manuals

I'd email him and save a few bucks, that way you can also download - no
waiting for a CD.

I sent an email, and the search now finds it. It's more $ than the
Qservice manual that tm linked to.

On 11/8/2012 8:38 PM, wrote:
"I never turned it off and it is still working. I will leave it powered on
until this project is completed and then look for a new function generator. "

You are SO looking at bad capacitors. If it stops working when you are done and you need it again, put it in the oven on keepwarm. Or change the capacitors of course.

J
Spoken like a man with experience.
How many DEAD FG507's have you fixed by replacing caps?
Which caps?
Please share so others can benefit.

Do I have to actually fix that particular model to have enough experience to know that tings that have trouble starting up usually have bad caps ?

J

On 11/9/2012 4:44 PM, wrote:
Do I have to actually fix that particular model to have enough experience to know that tings that have trouble starting up usually have bad caps ?

J
My pet internet peeve is people who state with certainty and authority,
things they know nothing about.

I stopped short of criticism and asked about your credentials.
It appears that you have none in this area.

If you looked at a pile of dead LCD monitors, it's likely that a
many of them would have bad caps.
If you looked at a pile of dead TM500 stuff from the FG507 era,
it's likely that ZERO of them died from bad caps.

As I stated, that model post-dated my tenure in TM500 design,
but not by much.
I can almost guarantee you that the FG507 won't stop working
intermittently because of "bad caps".
The symptom of bad caps will be hum on the output and FMing.

Are we having fun yet?

"Are we having fun yet? "

Getting there.

"If you looked at a pile of dead TM500 stuff from the FG507 era,
it's likely that ZERO of them died from bad caps. "

I read the OP. It didn't die. It fails to start. There is a difference. If you think I was recommending a bunch of caps be changed at random you are mistaken. Any digital thing need proper reset and Vcc or Vdd or whatever to run. If it is not there initially it will never run. If there eventually it will run forever, but only gets one chance to start.

That's what I read in the OP. Also, being the type of equipment it is, it's not likely to be a bunch of caps, just one. It is most likely from the description in the OP. I would be looking at whatever feeds the microprocessor(s) and the associated reset circuits, unless they are all internal. That would be my first thing to do, even though it is not a common failure. (of course it is possble the OP already looked into that)

I have an intenet filter in my brain. When someone writes something I know that it is just one person saying it and they could be worng, as can I. Maybe I should have phrased it differently, maybe others do not have that automatic filter. You save alot of keystrokes by not including all the "maybe", "could be" and all that every time. I thought it was a foregone conclusion that it was just a suggestion.

I never claimed to have fixed one of those generators with the exact same symptom and it was C XXX or whatever.

This is not worth an argument really. I will just take note of what you wrote and perhaps phrase things a bit differently in the future.

J

On 11/10/2012 1:17 PM, wrote:
"Are we having fun yet?"

Getting there.

"If you looked at a pile of dead TM500 stuff from the FG507 era,
it's likely that ZERO of them died from bad caps. "

I read the OP. It didn't die. It fails to start. There is a difference. If you think I was recommending a bunch of caps be changed at random you are mistaken. Any digital thing need proper reset and Vcc or Vdd or whatever to run. If it is not there initially it will never run. If there eventually it will run forever, but only gets one chance to start.

That's what I read in the OP. Also, being the type of equipment it is, it's not likely to be a bunch of caps, just one. It is most likely from the description in the OP. I would be looking at whatever feeds the microprocessor(s) and the associated reset circuits, unless they are all internal. That would be my first thing to do, even though it is not a common failure. (of course it is possble the OP already looked into that)

I have an intenet filter in my brain. When someone writes something I know that it is just one person saying it and they could be worng, as can I. Maybe I should have phrased it differently, maybe others do not have that automatic filter. You save alot of keystrokes by not including all the "maybe", "could be" and all that every time. I thought it was a foregone conclusion that it was just a suggestion.

I never claimed to have fixed one of those generators with the exact same symptom and it was C XXX or whatever.

This is not worth an argument really. I will just take note of what you wrote and perhaps phrase things a bit differently in the future.

J

It's unlikely that there's anything digital in that FG507...unless you
want to call
the trigger comparator digital.

It's unlikely that there's anything digital in that FG507...unless you want to call the trigger comparator digital.

I find that a bit hard to believe but surely is possible. Maybe I'll just STFU now lol. And no, even if a comparator is considered digital that's not what I meant. I guess the thing is older than I thought.

So really, what do you think is wrong with it ?

J

On 11/10/2012 8:02 PM, wrote:
It's unlikely that there's anything digital in that FG507...unless you want to call the trigger comparator digital.

I find that a bit hard to believe but surely is possible. Maybe I'll just STFU now lol. And no, even if a comparator is considered digital that's not what I meant. I guess the thing is older than I thought.

So really, what do you think is wrong with it ?

J

late 70's design.

My first response discussed the likely power supply topology and things
to look for.
My money was on the pass transistors coming unsoldered from the backplane.
He seems to have eliminated that possibility.

The symptoms were not clear. "No joy" is insufficient specificity to
provide much help. I made the rash assumption that the power light was off,
but who knows.
There are a bunch of mainframe issues. They get bent.
The fiberglass is abrasive and wears the socket and can lead to
misalignment of the contacts and intermittent contact.
The instrument is likely very simple and should be easy to figger out
with a scope.

"mike" wrote in message
...
On 11/10/2012 8:02 PM, wrote:
It's unlikely that there's anything digital in that FG507...unless you
want to call the trigger comparator digital.

I find that a bit hard to believe but surely is possible. Maybe I'll just
STFU now lol. And no, even if a comparator is considered digital that's
not what I meant. I guess the thing is older than I thought.

So really, what do you think is wrong with it ?

J

late 70's design.

My first response discussed the likely power supply topology and things to
look for.
My money was on the pass transistors coming unsoldered from the backplane.
He seems to have eliminated that possibility.

The symptoms were not clear. "No joy" is insufficient specificity to
provide much help. I made the rash assumption that the power light was
off,
but who knows.
There are a bunch of mainframe issues. They get bent.
The fiberglass is abrasive and wears the socket and can lead to
misalignment of the contacts and intermittent contact.
The instrument is likely very simple and should be easy to figger out
with a scope.

There is no processor in the FG507.

The main capacitors are in the mainframe. This unit does not use the AC
voltages from the mainframe.

One thing to take a look at is the IC sockets. If they are the TI type, it
would be the first thing to check as it is a known issue.

You might google for information on that problem.

Have fun,

tm

wrote:

"Are we having fun yet? "

Getting there.

"If you looked at a pile of dead TM500 stuff from the FG507 era,
it's likely that ZERO of them died from bad caps. "

I read the OP. It didn't die. It fails to start. There is a difference. If you think I was recommending a bunch of caps be changed at random you are mistaken. Any digital thing need proper reset and Vcc or Vdd or whatever to run. If it is not there initially it will never run. If there eventually it will run forever, but only gets one chance to start.

That's what I read in the OP. Also, being the type of equipment it is, it's not likely to be a bunch of caps, just one. It is most likely from the description in the OP. I would be looking at whatever feeds the microprocessor(s) and the associated reset circuits, unless they are all internal. That would be my first thing to do, even though it is not a common failure. (of course it is possble the OP already looked into that)

I have an intenet filter in my brain. When someone writes something I know that it is just one person saying it and they could be worng, as can I. Maybe I should have phrased it differently, maybe others do not have that automatic filter. You save alot of keystrokes by not including all the "maybe", "could be" and all that every time. I thought it was a foregone conclusion that it was just a suggestion.

I never claimed to have fixed one of those generators with the exact same symptom and it was C XXX or whatever.

This is not worth an argument really. I will just take note of what you wrote and perhaps phrase things a bit differently in the future.


We had our own calibration lab at Microdyne, and they replaced a lot
of electrolytic capacitors in test equipment. That function generator
is decades old, and a lot of places left test equipment powered up 24/7
so those failures are to be expected. Some factories aren't air
conditioned, ao that shortens the life even more.

wrote:

It's unlikely that there's anything digital in that FG507...unless you want to call the trigger comparator digital.

I find that a bit hard to believe but surely is possible. Maybe I'll just STFU now lol. And no, even if a comparator is considered digital that's not what I meant. I guess the thing is older than I thought.

So really, what do you think is wrong with it ?


It looks like it was designed in the '70s.

Phto & specs:

http://www.teknetelectronics.com/Search.asp?p_ID=1661&pDo=DETAIL
http://www.teknetelectronics.com/DataSheet/TEKTRONIX/TEKTR_FG500series84819.pdf

"mike" wrote in message ...

On 11/10/2012 8:02 PM, wrote:
It's unlikely that there's anything digital in that FG507...unless you
want to call the trigger comparator digital.

I find that a bit hard to believe but surely is possible. Maybe I'll just
STFU now lol. And no, even if a comparator is considered digital that's
not what I meant. I guess the thing is older than I thought.

So really, what do you think is wrong with it ?

J

late 70's design.

My first response discussed the likely power supply topology and things
to look for.
My money was on the pass transistors coming unsoldered from the backplane.
He seems to have eliminated that possibility.

The symptoms were not clear. "No joy" is insufficient specificity to
provide much help. I made the rash assumption that the power light was off,
but who knows.
There are a bunch of mainframe issues. They get bent.
The fiberglass is abrasive and wears the socket and can lead to
misalignment of the contacts and intermittent contact.
The instrument is likely very simple and should be easy to figger out
with a scope.

Thanks mike. I always had a power light. The FG is still running (I will
not turn it off until later) as my project is not over and I don't want to
risk that it won't start again.

My guess is that the mainframe is OK as my other plug-ins all work fine.

The FG is repairable but difficult if there is no extender card available!

On 11/11/2012 1:31 PM, Charles wrote:


Thanks mike. I always had a power light. The FG is still running (I will
not turn it off until later) as my project is not over and I don't want
to risk that it won't start again.

My guess is that the mainframe is OK as my other plug-ins all work fine.

The FG is repairable but difficult if there is no extender card available!

I jumped to the "dead" conclusion.
You're likely right about the mainframe if you switched holes.
But don't generalize that to any failure modes. There are hole
specific functions that can cause problems.

You still need all the supplies working, so check that.
What were the exact symptoms of "not working"?
What was the output voltage? did it vary with offset/amplitude
settings? Did it vary with the frequency dial setting?
waveform settings changes?
See any output glitches when you changed frequency ranges?
What did the sweep settings do? It's possible for a failed
sweep to cut off the current to the ramp.
If there's a sweep output or a trigger output, see if anything
comes out there.

It's basically a pair of current sources charging a cap.
The triangle is the basic waveform function.
It gets "rounded off" for sine wave. Square comes out
of the peak comparator. Make the triangle work first.

It's a two-wide plugin. If it has two connectors out the back,
your extender problems multiply. Depending on the internal
connections between boards, you may need extenders there too.

Assume if you had a service manual, you'd have said so?
Try to find it.

"mike" wrote in message ...

On 11/11/2012 1:31 PM, Charles wrote:


Thanks mike. I always had a power light. The FG is still running (I will
not turn it off until later) as my project is not over and I don't want
to risk that it won't start again.

My guess is that the mainframe is OK as my other plug-ins all work fine.

The FG is repairable but difficult if there is no extender card available!

I jumped to the "dead" conclusion.
You're likely right about the mainframe if you switched holes.
But don't generalize that to any failure modes. There are hole
specific functions that can cause problems.

You still need all the supplies working, so check that.
What were the exact symptoms of "not working"?
What was the output voltage? did it vary with offset/amplitude
settings? Did it vary with the frequency dial setting?
waveform settings changes?
See any output glitches when you changed frequency ranges?
What did the sweep settings do? It's possible for a failed
sweep to cut off the current to the ramp.
If there's a sweep output or a trigger output, see if anything
comes out there.

It's basically a pair of current sources charging a cap.
The triangle is the basic waveform function.
It gets "rounded off" for sine wave. Square comes out
of the peak comparator. Make the triangle work first.

It's a two-wide plugin. If it has two connectors out the back,
your extender problems multiply. Depending on the internal
connections between boards, you may need extenders there too.

Assume if you had a service manual, you'd have said so?
Try to find it.

For now, I am going to rule out the mainframe as all the other plug-ins are
working normally (PS501-1, PS502-2, SG503).

With no extender board, I don't think a service manual will help much.

Thanks again.

On Sun, 11 Nov 2012 18:28:16 -0500 "Charles"
wrote in Message id: :


With no extender board, I don't think a service manual will help much.

Ahh, but you can buy one of those as well. And the Price Is Right.
http://www.jammaboards.com/store/tek...tm500-kit.html

"JW" wrote in message
...
On Sun, 11 Nov 2012 18:28:16 -0500 "Charles"
wrote in Message id: :


With no extender board, I don't think a service manual will help much.

Ahh, but you can buy one of those as well. And the Price Is Right.
http://www.jammaboards.com/store/tek...tm500-kit.html

Or you can remove the covers from the TM500 power supply and get to most
everything in the plug in. Or at least the main board of the 507.

On Mon, 12 Nov 2012 05:39:27 -0500, JW wrote:

On Sun, 11 Nov 2012 18:28:16 -0500 "Charles"
wrote in Message id: :


With no extender board, I don't think a service manual will help much.

Ahh, but you can buy one of those as well. And the Price Is Right.
http://www.jammaboards.com/store/tek...tm500-kit.html

Instructions:
http://tektronix.jammaboards.com/Make_your_own_Tektronix_TM-500_extender.pdf

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"JW" wrote in message ...

On Sun, 11 Nov 2012 18:28:16 -0500 "Charles"
wrote in Message id: :


With no extender board, I don't think a service manual will help much.

Ahh, but you can buy one of those as well. And the Price Is Right.
http://www.jammaboards.com/store/tek...tm500-kit.html

Thanks for the link. I might just go to work on this.

"Charles" wrote in message ...

I fired it up today and no joy. Took off all the covers/shields and tested
all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely on
it now. Any suggestions?

Lots of helpful replies here, but looking for alternatives, I found this:
http://www.neobits.com/instek_sfg_21...FRRbnAodpnoAgQ

No way that I am going to pay for a schematic/service manual (from a
questionable source) and pay for an adaptor to power the FG507 so I can work
on it when the link above promises so much more.

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

Thanks!

On 11/17/2012 4:13 PM, Charles wrote:


"Charles" wrote in message ...

I fired it up today and no joy. Took off all the covers/shields and tested
all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely on
it now. Any suggestions?

Lots of helpful replies here, but looking for alternatives, I found
this:
http://www.neobits.com/instek_sfg_21...FRRbnAodpnoAgQ

A function generator is a jack of all trades, master of none.
Choosing one is the art of minimizing the problems caused by the crappy
waveforms
in your specific application.
Without knowing which waveforms and functions are important to you and
what imperfections you
can tolerate, there's not much help anyone can provide.
The specs in large print on the datasheet usually don't tell the whole
story.
It's a lot like buying an automobile and expecting to actually get 40mpg.

No way that I am going to pay for a schematic/service manual (from a
questionable source) and pay for an adaptor to power the FG507 so I can
work on it when the link above promises so much more.

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

Thanks!
If you're gonna scrap it, send it to me.
I'll fix it and add it to my collection of Tektronix Relics.

On Sat, 17 Nov 2012 19:13:18 -0500, "Charles"
wrote:

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

You're willing to pay $400 for a replacement function generator, but
not $15 for a schematic to repair the one you currently own.

It's easy enough to calculate the relative cost of repair to replace.
My guess(tm) is that it would take me about 2 hrs and $20 in parts to
replace all the dip tantalum capacitors in the FG507. A little
Googling will show that old tantalums are a major problem in Tek
products. I value my spare time at $35/hr. That's $90 cost to repair
the FG507 without the risk of buying a manual from a questionable
source. Working blind does offer a challenge, but I suspect that's
not why you don't want to spend the $15. I would recommend a manual
as it's often difficult to read the markings and color codes on old
tantalums. Good luck.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Sat, 17 Nov 2012 19:13:18 -0500, "Charles"
wrote:

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

You're willing to pay $400 for a replacement function generator, but
not $15 for a schematic to repair the one you currently own.

It's easy enough to calculate the relative cost of repair to replace.
My guess(tm) is that it would take me about 2 hrs and $20 in parts to
replace all the dip tantalum capacitors in the FG507. A little
Googling will show that old tantalums are a major problem in Tek
products. I value my spare time at $35/hr. That's $90 cost to repair
the FG507 without the risk of buying a manual from a questionable
source. Working blind does offer a challenge, but I suspect that's
not why you don't want to spend the $15. I would recommend a manual
as it's often difficult to read the markings and color codes on old
tantalums. Good luck.


--

I found the manual at Qservice for $8 US. Operator and service manual. Two
gamma extenders would take will take about an hour to build up and you will
have them for the future. Or just remove the TM50x cover and you can reach
most anything. I doubt it is a shorted tantalum cap. More likely a switch or
pot that needs cleaning.

But I suspect the OP does not possess either the skill or desire to dig into
this. So he could just put the TM and the FG up on ebay and help cover the
cost of the non-repairable Chinese function generator. Also, good luck.

On 11/18/2012 10:20 AM, Jeff Liebermann wrote:
On Sat, 17 Nov 2012 19:13:18 -0500, "Charles"
wrote:

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

You're willing to pay $400 for a replacement function generator, but
not $15 for a schematic to repair the one you currently own.

It's easy enough to calculate the relative cost of repair to replace.
My guess(tm) is that it would take me about 2 hrs and $20 in parts to
replace all the dip tantalum capacitors in the FG507. A little
Googling will show that old tantalums are a major problem in Tek
products. I value my spare time at $35/hr. That's $90 cost to repair
the FG507 without the risk of buying a manual from a questionable
source. Working blind does offer a challenge, but I suspect that's
not why you don't want to spend the $15. I would recommend a manual
as it's often difficult to read the markings and color codes on old
tantalums. Good luck.


There are many well-meaning people who probably weren't even born
when the FG507 was designed. The current plague of bulging/open
computer/monitor caps simply does not apply to that era.
Yep, caps did fail, but ripping out all the caps probably won't
fix anything intermittent from that era.

A little history.
In the '70's, Tek used a LOT of teardrop tantalum caps. They were
very aware of the failure mode. The design guideline for tantalums
was changed to require significant voltage derating and an equivalent
resistance in series of something like 3 Ohms per volt...from memory...
That all but eliminated use of teardrop tantalum caps in new designs
by engineers who actually followed the guidelines. But there were a zillion
of them still in the field.

Tantalum caps have two modes. They work fine, or they're shorted.
That's not leaky, or a little bit shorted. They're DEAD shorted.
Once shorted, they never come back. I've never seen an intermittent
tantalum cap.
The short resistance is so low that it's difficult to get them hot...
but if you do have a HIGH current source, you can cause them to
explode. That's not an intermittent process either.

You can check most tantalum caps by poking an ohm-meter at 'em in circuit.
IF they're shorted, you can tell. It's rare to have a circuit resistance
low enough to mask the shorted tantalum cap.

"mike" wrote in message ...

Big snip.

I am pretty sure it's a gain problem perhaps related to a low supply
voltage. Once it started, it ran fine for days. When gain is on the hairy
edge, oscillators get iffy. They have trouble starting.

Nice people here, all trying to be helpful and I appreciate that.

Thanks Mike and thanks to all of you.

On 11/18/2012 2:19 PM, Charles wrote:


"mike" wrote in message ...

Big snip.

I am pretty sure it's a gain problem perhaps related to a low supply
voltage. Once it started, it ran fine for days. When gain is on the
hairy edge, oscillators get iffy. They have trouble starting.

I've never seen the schematic, but I have done design reviews on
the FG501/2/3/4.
It's extremely likely that the oscillator is a cap with switched
current sources and threshold detectors determining the amplitude
of the triangle.
"Trouble starting" is likely not relevant.
You need to consult someone locally who knows how 1970's function
generators work...or do some googling. Well-meaning random inputs
from net denizens who don't have any relevant experience is often
counter-productive.

The FG507 topology is likely to be very similar to this:
http://bama.edebris.com/manuals/tek/fg503
with some sweep stuff bolted on.
The sweep is irrelevant except that it's possible for
one of the sweep tentacles to disable an otherwise working
triangle generator.
The components used to implement the circuit vary over time,
but the topology hasn't changed in decades.

This one is probably closer to the FG507 and worth downloading,
but understand the FG503 before
you delve into the complexity of the FG504. There's some stuff
in the 504 that is counter-intuitive and put there to patch up
some fundamental design flaws without a complete redesign.

http://bama.edebris.com/manuals/tek/fg504

Nice people here, all trying to be helpful and I appreciate that.

Thanks Mike and thanks to all of you.

On Sun, 18 Nov 2012 14:02:27 -0800, mike wrote:

Yep, caps did fail, but ripping out all the caps probably won't
fix anything intermittent from that era.

It worked nicely on a Tek 465 scope and a Wavetek 3000b service
monitor. See below.

Tantalum caps have two modes. They work fine, or they're shorted.
That's not leaky, or a little bit shorted. They're DEAD shorted.
Once shorted, they never come back. I've never seen an intermittent
tantalum cap.
The short resistance is so low that it's difficult to get them hot...
but if you do have a HIGH current source, you can cause them to
explode. That's not an intermittent process either.

I've seen a third mode with tantalums on power supply lines. They act
like a short when cold causing any current limiting or foldback
circuit to shut down the power supply. However, if you apply voltage
long enough (usually about 10-20 seconds), the cap will recover
causing the circuit to recover. I learned this the hard way after
designing far too many 10uf 25v tantalums (mostly Murata) into marine
radios running on 12V battery power. However, it took 20-30 years for
the problems to appear.

You can check most tantalum caps by poking an ohm-meter at 'em in circuit.
IF they're shorted, you can tell. It's rare to have a circuit resistance
low enough to mask the shorted tantalum cap.

If I can get the power supply to cooperate, I've have really good luck
with a borrowed thermal imager, an optical IR thermometer, and/or a
thermocouple thermometer. The thermocouple probe works best as I can
walk it around the PCB rather quickly. It doesn't take long for the
caps to get warm.

When they burn up, it's rather impressive. It starts with a dull red
glow, gets brighter, and eventually hits incandescence. It also
belches copious amounts of toxic smoke. One of the early IBM PC
clones had tantalums for bypass caps. One was in backwards. The
customers called and asked "My computer is on fire. What should I
do?" I answered "Turn it off". I hear the distinctive click of the
IBM PC style on/off switch over the phone.

From the description and details provided by the original poster,
there's not much more that can be deduced without additional
measurements. If something is holding down the (linear?) power
supply, it would be interesting to see what the power supply is doing.
A DVM on the power supply lines, or a watt meter on the AC input, will
offer some indication of what it's doing.

Note that an FG507 recently sold for $80.
http://www.liveauctionworld.com/TEK-FG507-GENERATOR_i11032006
The most economical approach would be to find another at about this
price. Then compare voltages and waveforms between the two units to
fix the original. If it's that important an instrument, a spare would
be a good idea. It also avoids having to spend $8 or $15 on a manual.

Incidentally, the FG-507 originally sold for about $2,220.
http://www.ko4bb.com/Manuals/Tektronix/Tektronix_-_TM-5000_Series/Tek_FG5010_short_form.pdf


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 18 Nov 2012 16:01:38 -0800, Jeff Liebermann
wrote:
(...)

Also, you may need a TM502a mainframe schematic if you suspect the
power supply to be at fault.
http://www.ebay.com/itm/390216672603
$7.50



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 11/18/2012 4:15 PM, Jeff Liebermann wrote:
On Sun, 18 Nov 2012 16:01:38 -0800, Jeff
wrote:
(...)

Also, you may need a TM502a mainframe schematic if you suspect the
power supply to be at fault.
http://www.ebay.com/itm/390216672603
$7.50



I don't understand why people do stuff the hard way...
http://bama.edebris.com/manuals/tek/tm503
FREE

On Sun, 18 Nov 2012 17:54:36 -0800, mike wrote:

On 11/18/2012 4:15 PM, Jeff Liebermann wrote:
On Sun, 18 Nov 2012 16:01:38 -0800, Jeff
wrote:
(...)

Also, you may need a TM502a mainframe schematic if you suspect the
power supply to be at fault.
http://www.ebay.com/itm/390216672603
$7.50

I don't understand why people do stuff the hard way...
http://bama.edebris.com/manuals/tek/tm503
FREE

Ummm.... because I was looking for a TM502a, not a TM503. I didn't
think of searching BAMA (oops) for variations and mutations. Thanks.

Looking at the schematic, I see two overtemp thermostatic switches (S2
and S3) which might be part of the problem. There are two types,
thermal fuses and thermal switches. The parts list description an a
barely readable Sensata catalog page says switch, but I think it's
really a fuse. It's a stretch, but a bordeline thermal switch
activation might fit the symptom.

Also, as you previously mentioned, the power transistors might gone
intermittent where they're soldered to the backplane. The 4500uf 40v
caps might have dried out and/or need reforming, which would show up
as high leakage current. That could be tripping the thermal switches
or blow the fuse until the caps have warmed up somewhat.
http://www.qsl.net/g3oou/reform.html (simple)
http://www.nmr.mgh.harvard.edu/~reese/electrolytics/ (detailed)


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558