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.