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looking for schema and service manual for an ancient 3bx ATC21 260385-02

m6969pm6969p antique vinylPosts: 1

for some direct cut pressings I like to maintain a completely analog rendering train
so I use tube pre-amps (for linearity),
hysteresis free matching only
avoid semiconductors where possible or drive them close to zero to stay as linear as possible
membrane speakers and earphones (no coils)

I have two 3bx

I did download the manuals from here: there are two but they are the same file

the markings on my circuit boards are

dbx ATC21
260385-02

The schematics I downloaded are kind of matching but not. Seems to be a newer version than what I have.

both were bought online, supposedly 'working'

yes, the lights do flicker... not the right way
one has a bad humm,
the other works on one channel only, no hardware faults seem to be present, I suppose someone 'fixed' it.

looking at the boards, someone clearly must have messed with the potentiometers, at least one is way out of the others, usually in such circuits they stay pretty much the same (symmetry pot) for similar circuits.
A sign someone messed with it and did not get it back how it belongs.

This is great discrete technologies, I am very familiar with it. As kids we built short wave, and FM receivers, we built our own power amps (pretty nasty ones I need to say now), and speaker walls.

The schema does not match the circuit board: where the checkout procedures sees a 353 there is a 351, it's a holy mess arranged for a pretty backwards limited robot, so components are aligned to robot needs and capabilities and conductor lines snaking around and through in pretty ancient patterns.

Of course I can follow the signals and analyze the entire thing. Trying first if someone has the matching schema and checkout procedure.

Just asking, when you read this you might have that one friend who actually has one...

Of course 'new is better', not discussing anything, want to render it as it was when the vinyls were pressed.

Mike

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