Suddenly Lost Stereo Buss Monitoring On The 388

Mark7

Mark7

Well-known member
I was trying to set up mixer channel 2 (guitar amp mic) to record to track 3 . I set the input selector to mic, turned the trim up, set up mixer channel 2 (assign 3/4 on, panpot full left, channel, pgm left and stereo faders all in safe zone), then monitoring for track 3, made sure the stereo option was selected in the section underneath the tape deck, and got... Nothing. The same with channel 1 (vocal mic). just to make sure I disconnected the access send/receive jacks but still nothing. d I need to replace something or am I having a brain fart? Note, I was monitoring through headphones. Which I have no other way of testing.
 
Is the problem the same at the MONITOR OUT jacks?

What is the state of the PGM/CUE switch?

What are the states of the track arming switches?
 
According to my eyes, it's in the Up/Off position.

The stereo select switch is engaged on the right hand panel. Monitor volume is up. There's a hum
 
And can you verify no L-R assign switches are latched (down position) on input channels 1-8?
 
Update. I haven't lost stereo/pgm buss monitoring... I've done something stupid and fried the mic circuit (thought it'd be a neat idea to connect a bass directly to a mic input, because that's what Macca did, right?, turns out it probably wasn't). Line circuit is working fine. Plugged a Casio into a couple of line ins, set it up. got sound through headphones from 388.

Oh God, I'm so embarrassed. I totally forgot how impedance works
 
Glad you know what the problem is.

I didn’t think to ask if you verified the input was working, because you indicated in your first post you tried multiple inputs (referred to channels 1 & 2).

I think rather than impedance, the problem is signal strength. Not sure what exactly you plugged into the MIC input, but the MIC input’s nominal level is 1mV, which is 1/300th of the LINE input nominal level, so you likely cooked something there because the source was too “hot.”
 
That's the conclusion I've come to. The question is... What?

Also, I only tried the XLR inputs on channels 1 and 2
 
Either my circuit reading skills are non-existent, or I can't see where all the mic level inputs would be connected together
 
I’m sorry…I don’t understand what you are either asking or what you are exploring and why.
 
I want to know if this is something that can be fixed or if it's definitely the end for this 388 (unless I only ever record line level instruments)? I honestly don't understand how plugging a bass into one mic channel can result in them all being disabled. It makes no sense
 
Okay. Now we’re getting somewhere. It was not clear to me at any point in the thread none of your mic inputs work.

So you have connected a verifiably known working dynamic mic to mic inputs 1-8 using a verifiably known good cable, and turned up each the respective trim controls, and checked for signal at each respective ACCESS SEND jack, and all of them are dead?
 
Okay. Here goes. I'm using my compressor as a level meter (in bypass mode)

Channel 1: Clapping from across the room I can see the green LEDs on the compressor moving in time with my claps
Channel 2: Same. No sign of any loss of volume
Channel 3: Ditto
Channel 4: Ditto
Channel 5: Ditto
Channel 6: Ditto
Channel 7: Ditto
Channel 8: Ditto

I also tried listening via the aux buss (suggested by someone else, elsewhere). Here are the results

Channel 8: Ja, sehr gut
Channel 7: Oui. tres bien
Channel 6: Not good. Some sound, but lower than channels 7 and 7, and some distortion
Channel 5: I have sound through the main monitor buss (and the needle on track/pgm VU meter 1 is moving), but no sound from the aux buss
Channel 4: No sound from main monitor or aux buss. VU not responding
Channel 3: Same as 4
Channel 2: Same as 4
Channel 1: Same as 5
 
So your testing methods are unorthodox, and I’m not 100% confident they are conclusive, but I’m not sure how to ratchet that down and navigate that process, so I’m going to just say to your previous concern about your mic inputs, by virtue of what you shared above, signal is coming through all of them. They are working. So…what is not working?
 
I don't have access to the kind of testing equipment you have, so I did the best I could with what I had at hand. The test using the access sends and compressor shows that signal is getting through the circuitry but, on most channels, it's getting lost at some point before it reaches the monitor buss. To make things more confusing the aux buss works on 2 channels (7 and 8), but not on the rest. Can't figure out what might be causing that. Also, monitoring on channel 1 wasn't working at all when I started this thread. Yet today, with the same settings, it's suddenly back. What's up with that?
 
I don’t believe I indicated or suggested you needed sophisticated test equipment…all I said was plug in a mic, and monitor off the ACCESS SEND jack for each mic input…SEND to home hi-fi receiver input…anything with a line level input and speakers or headphone jack.

So anyway…your mic inputs are all working.

What’s up with intermittent signal issues? Welcome to vintage budget echelon analog audio gear. Some thoughts/comments:

1. Switch contacts oxidize and can completely interrupt signal…treatment with contact cleaner and exercising can help. Sometimes switches can be disassembled and contacts burnished. Sometimes switches need replaced.

2. Teac liked handling board-to-board interconnections via a phenolic resin-based PCB. I hate it. The solder joints are subject to failure because the PCB material is relatively non-robust. And the frame structures of devices like the 388 are less robust than more professional designs. This allows mechanical flexing and strain on the rigid PCB and solder joints. And also *every* time that board-to-board BUSS PCB needs to be removed there’s no way to do without risking compromising solder joints. IMO it is just a bad idea. If everything was glass fiber that would be a different story. Otherwise I think cable interconnects are a better idea long-term. So you may have multiple compromised or failed solder joints. Tip the 388 on its side, remove the bottom cover panel and while passing signal gently manipulate the BUSS PCB to see if the manipulation impacts signal flow positively or negatively.

Everything you are experiencing is not uncommon for something like the 388, and especially if it’s been taken apart at all. I tell you the truth, because of the phenolic resin-based PCBs, and the type of mini-Molex interconnections (which can be stubborn), *every* time you unplug something and plug it back in you run the risk of damaging a solder joint. And that’s just the way it is.
 
So, now I have PGM, Stereo and Aux buss monitoring on every channel except channel 2. Which only has aux (pre fader) buss monitoring.

And that's in playback mode as well.

But at least it's only one channel now
 
Okay.

I don’t understand what you mean by you have “Aux buss monitoring on every channel except channel 2. Which only has aux (pre fader) buss monitoring.” What is the difference between “Aux buss” and “aux (pre fader”? The AUX buss on the 388 is a pre-fader auxiliary buss. Period. So what don’t you have on channel 2?
 
I can hear program material recorded to track 2 if I have the aux mode select switch in the Up (pre-fader) position, but not in the down (post-fader) position. It's a two mode buss (one for setting up mono cue mixes, and the other for using it as a second effects send), signal comes back into the machine via dedicated stereo inputs
 
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