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?
ested
ly on
Bad switch contacts, did you check for any voltages after the pwer switch?
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 jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Manuals Plus claims to have a service manual.
You could also try asking on one of the Yahoo Tekscopes group.
Also, eBay for $14.50:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Huh. Yet Dave's webpage doesn't list it (I checked before posting the above.)
I'd email him and save a few bucks, that way you can also download - no waiting for a CD.
Also, Qservice has it for download as a PDF for $7.49
Good quality scans.
I sent an email, and the search now finds it. It's more $ than the Qservice manual that tm linked to.
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 jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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.
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.
It worked nicely on a Tek 465 scope and a Wavetek 3000b service monitor. See below.
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.
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. 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.
-- Jeff Liebermann jeffl@cruzio.com 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. $7.50
-- Jeff Liebermann snipped-for-privacy@cruzio.com
150 Felker St #D
I don't understand why people do stuff the hard way...
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. (simple) (detailed)
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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