Every Track On My 388 Monitors, Except 2

Nope, I was wrong. Track 2 records. I just can't monitor it via the monitor submix. In either record or playback.
 
I’d pull the bottom cover off and see if I could get signal to pass by gently manipulating connections that handle the signals path to/from the BUSS PCBs for the monitor mixer. Might just be a bad connection.
 
Yeah, that's the conclusion I came to as well. I'll do it tomorrow.

Note. My new avatar reflects the way I feel most of the time :D
 
See if you can get signal to pass to monitor mixer channel 2 by gently manipulating connections that handle the signal path to/from the BUSS PCBs for the monitor mixer.
 
I don't think I'm following you. Can you go into more detail; like step by step? Thanks
 
Mark7 said:
I don't think I'm following you. Can you go into more detail; like step by step? Thanks
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I think what he is suggesting is this: you’ll see wires inside that connect from one spot to another spot with these little plastic clips. If you wiggle those clips you’ll knock loose dust or corrosion and restore the connection. Maybe even one got jostled loose from vibration over the years.

You can even very very carefully tug them by grasping the plastic portion, not the wires, and pulling it off, then putting it back.

Just do the ones that connect to and from the BUSS circuit boards for now. The board may even say “BUSS PCB” on it in light green letters. That’s old stuff, so be gentle and don’t force anything, and do not tug on the wires themselves, only tug on the plastic plug.
 
Yes. Exactly. You’ve had that thing apart and back together plenty. The mixer cards with the monitor mixer level and pan controls…exercise the connections on the cards while monitoring monitor channel 2 to see if exercising or manipulating those connections has some affect on signal passing.
 
I've identified the connectors that connect the mixer channels to the monitor buss. I've given them a wiggle and even sprayed some contact cleaner on them, but no joy so far.
 
Update. After much wiggling there's sound coming from monitor submix 2, but it's still relatively weak compared to the other 7 monitor submixes and only with the volume pot all the way to the right
 
I’m not nearly as reliable troubleshooting these as SweetBeats but if I were you I’d be looking carefully for broken solder points in the areas you were just wiggling. So much old stuff has been dropped or rough-handled in its lifetime and those circuit boards get brittle—plus solder joints that weren’t perfect 50 years ago….i would even wiggle stuff while passing a signal. You might get the signal to turn on, then you can tell there’s a broken connection in that area.

I’d also deep clean that potentiometer with the correct no-solvent cleaning fluid.
 
So, as with other issues you’ve had in the past with this 388, it’s not a simple matter where anybody can tell you to do X and it will solve your problem. You have to get out the tone generator and level meter and start probing and find the fault. It is also possible the 4000 series switching ICs for the monitor sourcing are failed. There are other period Tascam devices with 4000 series logic ICs that are failed. I think U109 on the BUSS A PCB handles source control for monitor mixer channel 2.
 
AnalogApples said:
I’m not nearly as reliable troubleshooting these as SweetBeats but if I were you I’d be looking carefully for broken solder points in the areas you were just wiggling. So much old stuff has been dropped or rough-handled in its lifetime and those circuit boards get brittle—plus solder joints that weren’t perfect 50 years ago….i would even wiggle stuff while passing a signal. You might get the signal to turn on, then you can tell there’s a broken connection in that area.

I’d also deep clean that potentiometer with the correct no-solvent cleaning fluid.
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I agree. Plus it’s important to note Mark7 has had this 388 apart and reassembled more than once. The connections are not robust and have to be handled with care. And even if doing so there can still be damage inflicted with simple disassembly.
 
Which chip controls routing signal from mixer channel 2 to the stereo buss?

That's fine, so I guess it's not the same chip
 
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