On Sun, 21 Feb 2010 19:58:39 -0500, "Wild_Bill"
wrote:

The way I typically approach faults (without service literature) when there
is an identical, known good duplicate item, is to check input/output and
various other circuit points on the good one, making notes for comparison
when checking the faulty one.

The brown boards, as you probably know, are custom circuits, probably long
out of production/NLA.

That's a pretty good bet. And Sony is very stingy with information on
this stuff.


I'd just naturally suspect the blue tantalum capacitors, just because of
their age.

Easy and cheap to replace. How likely is it that 25 year-old tantalums
would be bad? Before the bad channel stopped working entirely it would
sometimes not work properly (though the symptoms were different than
the current problem) until the readout was powered up for a few
minutes, especially if it had not been used for a while. At that point
I was suspicious there might be a bad wet electrolytic cap that was
reforming under power. Can tantalums exhibit the same behavior?


If I found any obvious abnormalities in the signal comparisons, which is
very likely, I'd likely replace the 6 capacitors after a close inspection of
all the solder connections, as the easiest procedure/age upgrade.

There are a number of silkscreened designations on the board, which is a lot
better than none.

Yeah, and at least they are in English, though a bit cryptic.


It might be worthwhile to check the feedthrough vias (2 visible) for zero
resistance top/bottom, or just heat them up and fill with solder, and check
all the other soldered connections with a magnifier and reflow any that look
suspicious.

Again, it'd be easy to reflow all the joints. I'll do that.


The JAE jumper or the main connector could have some oxidation on the
contacts.

I pulled it and reinserted it with no change, but I'll do it a few
more times. All the connectors are gold plated and appear in good
condition, but I know that's no guarantee.

Marking the pot positions clearly before changing them is a good practice.

The cable lead terminals appear to be soldered instead of crimped, but
probably worthwhile to check them.

They're spring connectors on header pins. I've pulled and re-seated
them, but I'll check more thoroughly.

Thanks, Bill.

--
Ned Simmons