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Thread: Tascam 388 no right channel

  1. #11
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    Ok, so I checked this morning. When I first fired it up it was back to no right channel sound. So I pulled out my headphone cable and plugged it in to my mixdown deck and it was back to the weird mono thing. I then plugged the headphones back into the 388 and it was still doing the mono thing.

    Anyway, yeah, when I press the mono button the volume basically just gets louder, but does the same thing, where it's louder at the center and a little quieter when panned either way. With the mono button pressed and when it's not, it never actually pans when you rotate the knobs. It just gets equally quieter on both channels. Does that make sense?

  2. #12
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    Yes it does, but what are you monitoring exactly?

    Could you tell me, with as much detail as you can, where the material you are monitoring that is doing the weird mono thing comes into the 388, what those channel settings are, to where you have the channels assigned, and then those summing busses what their settings are? If it is tape playback you are monitoring how are you sourcing it, and what are those settings etc?

  3. #13
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    I'll try to be as thorough as possible. I have mostly been monitoring through tape playback and simply using the vertical monitor section. I have tracks that had already been recorded and I was using various tracks through the monitor section to test. I also tested the initial problem on mix mode and tried panning on all 8 channels and the issue was consistent.

    When I tested the stereo bus in yesterday, the issue was also the same in all manners tested. Weird mono problem with everything except the monitor outs, which were functioning as they should.

    I haven't tested the line in or XLR inputs for the channels since it switched to the mono issue, but I can this evening. When it was the no right channel issue, the pan on each individual channel was giving no sound when panned right with both line in and XLR. So if I had an input on channel one and panned left there would be sound on track one in rec mode, but if I panned right there would be no sound of I tried to record on track 2.

    If it would be helpful to try anything specific, I'll gladly try it when I get home.

  4. #14
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    Is it safe to assume when you are monitoring tape playback via the onboard MONITOR mixing section you are panning each track to taste using the pan controls, but they have no effect when the unit is exhibiting the weird mono issue except maybe to progressively diminish the level of the track somewhat when the respective PAN control is swept counter-clockwise or clockwise?

  5. #15
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    Yes, this is exactly what is happening.

  6. #16
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    Well I’ve not come across an issue like yours before. What’s confounding is, the way the unit was designed, if you are having trouble with signal at the STEREO OUT jacks you should also have that same problem at the MONITOR OUT jacks and the headphones. It’s possible to have problems at the MONITOR OUT jacks but not the STEREO OUT jacks, but not the other way around. So the way your problem is manifesting is really weird.

    There is a 14069 switching logic chip on the BUSS B PCB (maybe that’s the one you called the right buss PCB?), the one with all the PAN controls for the EFF returns as well as the monitor mixer channels. That logic chip, U104, controls muting transistors Q101~ 104...I can’t quite wrap my head around how that would cause your weird mono issue...no signal at all, yes, or one side only, yes, but not mono summing. But if it was me, based on past experience with that chip going belly up I’d shotgun it with a new part, and see where I was at.

    I can’t recall if you answered this one: how does signal input at the STEREO BUSS IN jacks reproduce at the MONITOR OUT and STEREO OUT jacks?

  7. #17
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    The stereo bus in causes the exact same problem as what I've described for tape playback in every way.

    The strange thing is with the stereo outs to the mixdown deck, the meters will correctly read the pan, but the headphone out of the mixdown deck is going the same mono thing. Not sure how the signal gets transferred to the deck via the unbalanced outs.

    I did switch out the BUS B PCB with one from my backup deck. I guess it's possible that both are bad. But now I can't remember if it was when I switched the PCB that the new mono thing started. I'm going to switch them again and see where that leaves me. Is the IC chip something I could find a new one of and solder onto the board?

    Someone also mentioned checking the post fader amplifier for the right channel. Would that be something to pursue?

  8. #18
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    Ok, I swapped the PCB bus B and it didn't change anything.

    When I first turned it on after swapping the PCB, the same thing that happened this morning happened again. The issue was initially no right channel. Then after a couple minutes I pulled the headphones from the 388 and plugged then into the mixdown deck and then the mono issue started up. The mono then kept going afterwards.

  9. #19
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    Absolutely weird. I wish I could get my hands on it and actually trace the signal.

    So when it’s doing WMT (weird mono thing) the issue is present in the stereo out jacks and in the headphones, but NOT the MONITOR OUT jacks??

    I don’t know if I can explain how weird this is...the post-fade stereo sum branches and one limb goes off to the unbalanced STEREO OUT jacks and the balance amp and then to the balanced STEREO OUT jacks and the meter amp. The other limb goes off to the monitor and headphone amps. But all are fed from the same stereo sum. Your issue presents as a bad stereo sum everywhere but the MONITOR OUT jacks, but the headphone amp and monitor amp sit right next to each other on the same PCB, and have the exact same source...it’s just a 3-pin mini Molex connector. And the issue is present at the STEREO OUT jacks suggesting the cause is somewhere after the signal goes to the meter amp but before it goes to the STEREO OUT jacks and the monitor and headphone amps, but the monitor out is okay... :???:

    You’re certainly welcome to replace the U104 logic chip, but it seems to me if that was the cause you would have the same issue at the monitor out jacks and the headphone jack...so just now something poked at my brain...I need to look at the operations section of the manual and refresh functional how the monitor mixer source is handled...there is auto source select circuitry there...

    If you end up wanting the part here is a link to one place to get it:

    CD4069UBE Texas Instruments | Mouser Europe

    But, again, I’m not certain that is your problem, and it sure would be a crazy coincidence if both BUSS B boards were bad...AND it doesn’t explain some other things.

    Oh and regarding checking the R fader booster amp you can do that, but the thing is when your 288 is doing the WMT you are getting audio in the R channel, just in a weird mono way, so the R amp is working.

  10. #20
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    Yeah I'm agreement it's unlikely that the chip is faulty in both PCBs. My goal for the summer is to one by one replace the caps on the various PCBs on this machine. When I'm ordering I'll order a backup chip since they are known for going out.

    So right now I've been more into tracking, which really doesn't require an accurate stereo field. Would it be harmful to operate the machine before this issue is solved? I'm going to have a some time over the next few weeks where I can make a little noise without bothering the neighbors.

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