Tascam 388 STEREO L issue

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coltj14

coltj14

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Hello all. Finally snagged myself a Tascam 388. To my knowledge everything works well EXCEPT this one issue.

STEREO L will begin to make a crackling/popping noise and then BOOM, there is no audio signal being sent to the left channel. Nothing to the headphones, stereo out, monitor out, or even a reading on the main VU meter.
When this crackling/popping sound does happen, the VU meter picks up that signal and shows a reading.
This issue has been very annoying because it will randomly do this. I haven’t noticed a trend in anything that I’ve done that would cause this issue.
The most I’ve been able to troubleshoot is that the fuses are A-Okay as I am a noob to these schematics.

If anyone is able to help with some advice and troubleshooting, I would greatly appreciate it.

Thank you.
 
Also it appears that the Right channel is louder than the Left channel
 
You probably need to replace the U104 chip on the Buss B PCB. This is a common failure with the 388 that manifests in a number of ways but always having something to do with the L-R buss, monitoring, etc. The part is cheap and readily available from places like Mouser and Digikey.
 
Thank you kindly. Would be able to point me towards the right direction of where I can find that in the machine?
 
The Buss B PCB is the one with all the effect return and monitor mixer pan pots on it.
 
After just screwing around and making tunes in mono, I noticed now that track 3 will drop out and sometimes when switch track 4 to either MIC or LINE, it will emit a loud high pitched screech for a few seconds and won’t do it again. I’m sorry to bombard this post with issues but I’d just prefer to fix it myself instead of spending a hefty amount on repairs.
 
You’re going to have to clarify…

Track = tape track

Channel = mixer channel

What are you talking about with #3 and #4? Tape tracks or mixer channels?
 
What is your experience level troubleshooting and repairing electronics, and what gear do you have to do this work?
 
My apologies. Mixer channels 3 and 4.

I’ve only worked with portastudio cassette decks in the past (knowing they had some issues). I was told that this 388 was in great working condition so it’s been quite the ride seeing new issues arise over time.
My dad is an electrician so I can always drive out to his place and borrow whatever tool is needed.
 
I would exercise the source select switches (the MIC - LINE - RMX switches…rapidly flip them back and forth maybe 50 times). Ideally I’d also jet some DeoxIT D5 in the switches and then exercise them, but I can’t recall if, even with the bottom panel off if you can get to the switch bodies to apply the DeoxIT when the cards are installed. The other thing I would do for intermittent signal issues with the input channels is exercise the ACCESS SEND/RCV jacks. Get a 1/4” TS cable. Rapidly insert and remove the plug into each SEND and RCV jack…there are normalling contacts in each jack and if they’ve not been used in forever and/or the machine has been in a humid environment these contacts can oxidize. Try that. If it doesn’t make a difference, try bypassing the normalling contacts by connecting a TS to TS cable from the SEND to the RCV jack of the problematic channel to see if that helps.

Back to U104 on the Buss B PCB…this may or may not be the cause of your L-R buss issue, but it is definitely a possibility, and if it doesn’t need done now (U104 replaced), it will in the future. 9 times out of 10 issues like yours are resolved by replacing U104 with a new part from a reputable vendor like Mouser or Digikey. I prefer new Texas Instruments branded parts when replacing 4000 series logic or switching ICs.
 
I greatly appreciate your help. Gonna order the chip and get back into the machine.
 
sweetbeats said:
I would exercise the source select switches (the MIC - LINE - RMX switches…rapidly flip them back and forth maybe 50 times). Ideally I’d also jet some DeoxIT D5 in the switches and then exercise them, but I can’t recall if, even with the bottom panel off if you can get to the switch bodies to apply the DeoxIT when the cards are installed. The other thing I would do for intermittent signal issues with the input channels is exercise the ACCESS SEND/RCV jacks. Get a 1/4” TS cable. Rapidly insert and remove the plug into each SEND and RCV jack…there are normalling contacts in each jack and if they’ve not been used in forever and/or the machine has been in a humid environment these contacts can oxidize. Try that. If it doesn’t make a difference, try bypassing the normalling contacts by connecting a TS to TS cable from the SEND to the RCV jack of the problematic channel to see if that helps.

Back to U104 on the Buss B PCB…this may or may not be the cause of your L-R buss issue, but it is definitely a possibility, and if it doesn’t need done now (U104 replaced), it will in the future. 9 times out of 10 issues like yours are resolved by replacing U104 with a new part from a reputable vendor like Mouser or Digikey. I prefer new Texas Instruments branded parts when replacing 4000 series logic or switching ICs.
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Great advice here, I have also dealt with intermittent right audio loss on my tascam 388 over the course of 8 years. Messing around with the dbx and stereo buttons has resolved the issue before, and it seems to self resolve and then randomly come back. I'm assuming, like you've said here, the U104 needs to be replaced is that a part that needs to be soldered? Not seeing U104 in stock at mouser, any other suggestions? Thanks for the help.
 
4069?

No…it should be a 4049…


Same part, but plug and play no solder? No. This is a 16-pin DIP IC. You have to remove the old part and solder in the new. There are no plug-in socketed ICs on a 388. If you want that you have to remove your old IC and solder in a socket.

U104 may or may not be the cause of your trouble. Yours sounds like a bad connection. When the chip goes bad it goes bad, it doesn’t come and go, at least that’s my experience. But that doesn’t mean you can’t try.
 
Thank you :guitar:
May be worth stocking up on the chip before it fails.
As far as bad connection, should I unplug connections in the monitor section where that 4049 chip is located and deoxit?
 
I think if it was me I’d start by tipping it on its side, removing the bottom cover and carefully manipulate boards and connections and see if I could make the problem happen. Question: is your intermittent R channel issue present in the monitor buss (headphones, R monitor out jack) as well as the R stereo out jack?
 
The European dealer Banzai Elec. sells two different 4049 chips, one buffered (4049B) and one unbuffered (4049UB). Looking the service manual of the 388, it indicates MC14049UBCP (CP is the pin format) for the Input/Meters PCB and MC14049B for the Buss B PCB. The link posted by Sweetbeats is the unbuffered one for Buss B PCB.

Is there really a difference between these two chip? It is no clear from the datasheets (at leats for me).
 
You’re over-thinking it. In this application the link I sent for the part works.
 
Thanks sweetbeats for the confirmation. You're right, sometime I'm really over-thinking!
 
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