It's been a number of years since I looked up the working principles of
magnetic linear scales, but Jon's recommendations about checking various
mechanical parts' fit/alignment/orientation is likely the best place to
start looking.

The tantalum cap problems I've encountered have been dead shorts, as Whit
commented, and if the current source is sufficient, the outer epoxy layer
may develop a pinhole with smoke shooting out of it (if you happen to be
watching as the power is applied).
Some tantalums seem to just fail abruptly when they get old.

The 3 silvery looking capacitors nearby are poly film types, and if it turns
out that there are signal abnormalities not related to physical/mechanical
parts alignment, it would probably be a good idea to replace the tantalums
and polys just because they're old.
Of course, replacing components can require service/calibration adjustments,
but having the properly working circuit is an advantage.

One other technique that has proved to be worthwhile, is to just rock the
pot positions back 'n forth a little, for a small portion of the rotational
range, after they've been clearly marked for their original positions.
This can sometimes create a better contact, in the event of a bit of
oxidation on the wiper.

If the outcome remains a mystery after making a reasonable amount of
comparisons to the working circuit and scale, the only option may be looking
for a replacement on eBay or surplus places that sell older encoders, linear
scales and similar instrument components. I remember seeing a couple of
surplus websites like that, but that would've been over 5 years ago.

I don't believe there is any way to find out what discrete components are
inside those custom hybrids, without destroying them.

--
WB
..........


"Ned Simmons" wrote in message
...
On Sun, 21 Feb 2010 19:58:39 -0500, "Wild_Bill"
wrote:


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?



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