[Robert Stevens]

I recently picked up one of these. The first 3 channels worked well out of the box. The last (4th) channel had some issues with thumping and still doing some gating even in the "out" position.

I was able to fix the thumping on channel 4 with the info in the manual about adjusting the "cntl rej" trimmer on the back of the unit.

I was also able to fix the second problem on channel 4 where the unit was still gating/expanding when in the out positon by adjusting a second trimmer pot inside the unit labeled "cnvtr symn". I, however, see no mention of this trimmer (or the one next to it "dist null") in the manual. They do show up on the schematic and looks like some sort a calibration for voltage dividers.

It would be nice to know what I am doing rather than just blind luck that adjusting the one pot solved my problem.

Finally, that one channel also seems to drop 2db in signal compared to the other 3 channels which drop 0db when in the out position or prior to gate/expansion threshold. Not sure what to look at there.

[Scott Dorsey]

Robert Stevens wrote:
I recently picked up one of these. The first 3 channels worked well out of=
the box. The last (4th) channel had some issues with thumping and still do=
ing some gating even in the "out" position. =20

Replace every electrolytic capacitor in the box. Some are leaky.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Robert Stevens]

I plucked all the electrolytics and ran ESR tests on all them. They all passed. However, they are all some pretty off brand so I'm gonna put some nichicon caps back in their place. Looks to me like someone recapped the unit at some point not that long ago. And of course, it was on of those folks that likes to bend the pins flush to the board making desoldering a PITA even with an electric vacuum pump tool.

[Scott Dorsey]

Robert Stevens wrote:
I plucked all the electrolytics and ran ESR tests on all them. They all pa=
ssed. However, they are all some pretty off brand so I'm gonna put some ni=
chicon caps back in their place. Looks to me like someone recapped the unit=
at some point not that long ago. And of course, it was on of those folks =
that likes to bend the pins flush to the board making desoldering a PITA ev=
en with an electric vacuum pump tool.

All of the symptoms you describe are the sort that are frequently caused by
leaky caps. Any time I hear thumping on a gate or VCA, my first thought
is there is DC someplace where there shouldn't be.

Don't worry about the pins being bent over. Cut off the capacitors on the
board side, then the desoldering tool will just remove the pin residue
quickly and completely leaving a nice clean hole.

Why did you remove the capacitors to do an ESR test? The whole point of
the ESR tester is that you can do rough quality checks in-circuit. Once
it's removed, you might as well just replace it anyway rather than trying
to salvage the original part.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."