VU Meter Woes

Working on a Marantz cassette deck with two VU meters.

One was dead, the other worked fine (after flushing the switches and pots). The dead one was dead — broken spring.

I was able to find a replacement meter and get it installed. It works perfectly, but now the meter that worked before doesn't respond!

I used a jumper to connect the brown wire (see below) to the magenta and it worked. But with that connection it's just mirroring the left channel. So this tells me it's something with the wiring and not the meter, correct?

Also note, the black wire is common, so to rule out a bad connection, I used a jumper to connect the two meters and it didn't change anything.

What I don't get is how the right side could work, then the left side is fixed and the right no longer works.

Here's a little sketch of how it's wired. Be gentle, I'm considering this a learning project...



The deck in question is a Marantz/Superscope CD 304. This is a tabletop unit, not a field recorder.

Any help would be amazing. Thank you.

Try running A with the B signal. That will tell you is the signal is present on the B channel.

I tried a jumper between A&B (brown and Magenta), are you saying completely disconnect B (magenta) and connect it to "A". Just want to clarify.

Thanks!

If it's not hard to do, yes, try running the A with the signal from the B channel.

De-soldered both meters. Used jumpers to try each set of wires on each meter, and a couple combinations just in case. The meters are fine, in all cases, the magenta wire was the no go.

Here is the weird thing though. When I was de-soldering the meters I accidentally made contact with a jumper to a tantalum capacitor (at least I think it was that) and a piece of random metal. Made the left VU meter go crazy. I'll try and get a photo, but it was nowhere near the magenta lead.

Sounds like there is a problem upstream. What troubleshooting tools do you have? An oscilloscope would be ideal, but not required.

Just a glint perhaps. many of these meters run off mv or m/amps in schematics so might look for circuit chip for same. (if needles seem to be free)
hope it helps.

@ryuuoh No dice on the oscilloscope. Just a multimeter, AK forums and google. This is truly one of those learning projects, as well as a possible lesson to stop buying things I can't fix.


@Binkman. Thanks for the tip. Ideally I need to find a schematic without paying too much more than I did for the deck. But since you mentioned it, and I'm not super familiar, could you give me some pointers as to what to look for?

Last thing. I went over the board last night and couldn't find an corroded connections or bad solders. Also, the caps were bulge and corrosion free.

Thanks all for your patience with me!

These meter circuits were pretty much the same across brands in that era. I would find a brand from that year, and cross the schematic with what you see on the board.
BTW, there are adjustment pots for the meters on that era gear, maybe give the problem channel pot a tweak.