Tascam 388 Rec Play Amp PCB troubleshooting

ethyrvalve

ethyrvalve

Norman Nanoweber
Hi all,
I'm just looking at somebody else's 388 right now and I got most of the bugs worked out (it was a sick puppy) but unfortunately there's a tricky no-repro issue (input is OK) that follows cards. I got the person to order a couple spare cards off of ebay but one of those too has a repro issue. By shuffling cards around I'm able to get things down to one channel with no repro. I also have two extra cards with one good channel each.
So far I've tested the ESR of all caps and swapped the electromechanical relays with known good ones.
Just wondering if there are any known issues I should be pin-pointing? Or if anyone has already gone through the agony of mapping out the correct voltages of a known good channel?
Looking at the schematic, it seems like an issue with the solid state relay could be a possible trouble spot or maybe the quad NOR gate TC4001PB?
 
For the record it ended up being one of the 220uf electrolytics. The problem was devious and tricky to troubleshoot because there was also a few cold solder joints on the mother PCB.
The moral of the story: Insist on proper packing (see this thread) if you buy one online.
 
Got a kick out of this. I was repairing a Tascam 38 (1/2" 8 Track), and having very similar issues. The thing was friggin' possessed. Fix one problem, another shows up. Get it all buttoned up, and CH5 isn't erasing, rip it all back apart. I swear... I wanted to throw the thing out the window several times. I ended up reflowing every solder jointon the mother board. And that was the root of 90% of the issues. I don't know that I will ever take on repair of another Tascam deck. The things are a PITA to work on!
 
At my shop, reflowing every solder joint on the motherboard is pretty much S.O.P. for several Tascam multitracks (30 series R2Rs, 388). Perfectly fine machines, but couldn't they have built them with plated-through fiberglass PCBs? (The higher end Tascam stuff - 48, MS-16 etc doesn't have any such problem)
 
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