[sdiy] Non-DIY, but looking for repair advice...

[John Ames]

On Mon, 13 May 2024 20:30:28 -0700
John Ames <commodorejohn at gmail.com> wrote:

> Well, I got it disassembled and reseated the connectors without
> fouling anything up, but it didn't do anything for the output level.
> I'll check the power rails next, but I'm curious - the service manual
> advises to check/trim PSU voltage between +/- 15V terminals on the
> PN1 2/2 board and the VE terminal on the JK board, but doesn't
> actually label any of the boards as the JK board in the diagram.
> Looks like the rear-panel jack board has a VE terminal - am I safe in
> assuming that's the one?

Update: had to go out and get a non-junk multimeter, but I was able to
get readings on the voltages at both the service manual's designated
test points and the VCA IC itself. Also checked the listed test points
for a few other voltages, though I couldn't get to the ones for +4.7 /
-9.7 without doing a full teardown. Here's what I found:

+15V (PSU):  15.05
-15V (PSU): -15.03
+15V (VCA):  15.06
-15V (VCA): -15.02

+1V (TP30):   0.96
+2V (TP31):   2.04
+4V (TP32):   4.05

Not exactly according to Hoyle, but I s'pose that's to be expected with
vintage gear; but is a few hundredths of a volt enough of a discrepancy
to cause serious drop in output level? Can't trim to spec at present,
as whoever fit the 115V regulator board didn't bother including the
trimmers...

(Also, though I doubt it has any bearing on anything, I noticed it so
I'll mention that something is giving off a faint but clearly-audible
clicking at the LFO rate - not pulses on the output, but put-your-ear-
next-to-it acoustic noise. Something in the LED driver circuit...?)