tascam 388 L/R assign....not working

T

towser

New member
My 388 has developed a problem. The L/R assign buttons don't work any more. I can't hear things plugged into the line inputs, or any of the tape playback using these buttons. I now have to monitor using the buss 1-8 assign buttons...anyone have any idea what could be wrong? I am the original owner of this unit...since 1988. I have the original manual. The thing is in exceptional condition, other than the L/R assign buttons....
Thanks for any help you can provide.
 
Thank you for posting. I have been looking at the monitor buss schematics....but I don't know how to troubleshoot them....for all I know it could be something else entirely. I'd really like to get the L/R assigns working again! ?
 
There is a logic chip that switches the monitoring source when you hit any one of the L/R assign buttons. I had a problem years ago on my 388 having to do with that function not working and ultimately it was that failed chip...pulled it from a card on the parts machine I had and replaced the failed one...back in business. Just can't recall if my issue was the same as why you are experiencing. It's all detailed in my Tascam 388 Story thread...I'll have to go digging.
 
Hi sweetbeats....I get no signal from the L/R buttons...none. If I'm using it as a stand alone mixer, or trying to listen to tape, ei: RMX. The switching logic chip you mention could very well be it. If so, what card/chip would it possibly be? Can I test the chip? Thanks.
 
You're going to have to wait...like I said I gotta go digging. :)

It's been years. Don't remember exactly what was happening and/or what card the Chip was on and which one it was. You are welcome to go looking at my 388 thread. It was near the end but before I sold it so a few pages back from the end.
 
Sweetbeats, thank you your follow up on this. I read your thread and it does sound like that chip could be the culprit. I get no sound using the L/R buttons from line inputs or tape playback. I really don't like hitting PCBs with a soldering iron ? could I clip out the old chip, leaving the legs up, and solder the new one to the legs? Also, how can I test the chip to see if its defective? Thanks so much for your help! Best regards.
 
I've done a lot of board-level soldering...I'd never want to try what you are suggesting on ANY chip, much less a 16-pin dip. You're welcome to try it, but I think it's a bad idea.

You need the right iron and a vacuum-type solder-sucker tool. My Antex pencil iron cost $15, is single temp...simple. Works fantastically.
 
I've done some PCB soldering as well. I'd hate to lift a trace. And my idea sucks, I know. I'd certainly rather take out the defective chip completely. I've been recording on the 388 again after years in the digital domain, and everything works and sounds great, with this exception.
Thanks for your replies, I appreciate them.
 
From what I can tell the ic chip u104 is a 14 pin chip. The mouser link is for a 16 pin. I'm hoping I can find a 14 pin...
 
The manual shows it as a 16-pin. That's actually good if its 14-pin. Can you put up a pic of the chip or at least get a part number off of it?
 
The part description # is mc14049b. I haven't pulled the buss b card yet, but looking at pics of the board on line, the chip "appears" to be 14 pin....not sure I can find one. When I pull the board, is there a way to test the chip before pulling it?
 
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Ok...looking at the schematic, it shows "mc14069ubcp"as the part description....which is a 14 pin. Also there are 2 FETs...Q103 & Q104 that may have something to do with the L/R buss issue..?
 
I recall teasing out whether or not the transistors Q103 and Q104 were part of the problem, but in my case they weren't. It was U104.

I'm sure there is a way to test U104 but yer askin the wrong guy. :)

Don't worry about a pic. When I go to mouser that part is only available in a 16-pin package. I'll dig a little further but I'm sure that chip is the same as the scads of them that are in my prototype Tascam console.
 
I didn't test them. Ruled out their participation in the problem by comparing my symptoms to the schematic and overall signal flow.
 
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