Tascam 388 : no playback signal

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IBS

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Hello everyone, I'd posted this problem of mine in the noob forum but was advised to come here!

I recently recapped/troubleshot a tascam 388 for a client. I'm mostly an "amp" guy, and don't really fully know my way around such a machine, but I figured his problems were simple enough (rewind was too slow and track 1 was weak) and with the manual I could get them sorted. And I did ! Everything was working fine afterwards, track one was not splendid but I got most of the signal back, and I fixed the rewind issue.

I've changed a few burnt components on the "Control" pcb, which I guess isn't affecting playback signal, but then again maybe I'm wrong...

During the process of recapping the Power Supply PCB I made a mistake and I put a polarized cap the wrong way around. When I turned the 388 on, everything seemed fine but the transport didn't work anymore. I turned the machine off, check the Power Supply PCB, re-soldered the cap the right way around, changed a fuse (F5) that had blown, and everything seemed to work great again. Except that I don't get any playback signal anymore!!

I'm working with known good headphones and brand new RMG tape. I know the Tascam does record because I've played the tape in another machine and I could hear what I had tried to record. I've followed the manuals instructions to the letter and still I'm not getting any playback signal. I've tried to play some pre-recorded tape, without any result either.

If I get the manual pictogram right, the "monitor logic control" decides how the signal is monitored, and sends it to the monitor "gain" and "pan" (I know what those are) and then to a "Stereo/Logic Monitor" section, and then to the main stereo master > monitor select > my headphones. I'm guessing one of these is the culprit, especially the ones between quotation marks (I can't figure out what/where those are).

Could you please please help ? I'm going crazy over this...
 
There is a hex inverter on the Mom B pcb that selects a pair of FETS to switch between using the monitor out or the mixer's outputs.Check/ rreplace that
 
wkrbee said:
There is a hex inverter on the Mom B pcb that selects a pair of FETS to switch between using the monitor out or the mixer's outputs.Check/ rreplace that
Click to expand...

Thanks for your answer. Before going any further with your suggestion I should mention:

I have no problem monitoring the input signal fed through the recording busses before/when recording. The monitor controls (gain, pan) and the PGM faders work properly then, and affect the signal as they should.

With that in mind should I still check that hex inverter and those FETs ?
 
I'd also like to mention : I did register on this forum to find people who'd be both informed and generous enough to help. I've browsed the site profusely and I've seen many request such as mine where the OP just seems to disappear after one or two kind answers were given to him, no thank you, not even a reply whether or not the trick worked (which could be useful for browsers). That's got to be frustrating for the people who've lent a hand.

I'm not like that, I really NEED to get this problem sorted, and I'm willing to report back until I see this through.
I feel like I've stuck my neck too far out with this machine and I've probably caused the problem myself too, which is something I'm very embarrassed about, having worked on quite a lot of audio devices without a mishap so far.
 
The 4 FETS select either the output from the monitor section or the stereo out.If the stereo buss in works but there is no stereo output from the mixer section then the hex inverter is bad-but don't forget to verify you plugged in the buss card correctly,(no offset pins or mis-connected connectors) ,and all the cables are connected correctly-none mixed up.
 
wkrbee said:
And you have the mixer input set to "tape" ;-O
Click to expand...

Thanks so much for your help.
A little busy at the moment but I'll try to locate that hex connector, replace it and I'll keep you posted !!
 
Hey wkrbee and other homerec forum users !

It took me ages to get to it but I finally went and located the quad gate on it that serves as a hex inverter (for reference it's a Motorola-made MC14011B) on the Control PCB (not Mother PCB) and it has a "brother" quad next to it. The former needed changing, the latter had dried solder joints. There were other dried solder joints on the PCB. The Tascam 388 is now up and running !

Thank you so much for your input ! I hope this thread will eventually help others troubleshoot their 388...
 
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