Tascam 388 - Routing problems.

[fizzicato]

I'm having a routing issue with my Tascam 388:


When I try to route a channel using the assignment buttons, tracks 1 and 2 receive the signal from every other bus except their own. For example, if I assign a channel to Bus 3-4, 5-6, 7-8, or even the L-R master bus, that signal bleeds directly into tracks 1 and 2. However, if I specifically press the 1-2 assignment button, tracks 1 and 2 receive absolutely nothing.


Essentially, the internal routing for tracks 1 and 2 is doing the exact opposite of what it's supposed to do: it picks up all the traffic from the other busses but rejects its own.


Has anyone encountered a similar issue? Could this be a failing component on the program buss board, a bad op-amp, or perhaps dirty switches/grounding issues? Thanks in advance for any advice or troubleshooting tips you can share

 

[sweetbeats]

So you can’t get anything to PGM group 3-8 or to the L-R master buss?

How are you monitoring the signal? Are you monitoring through the monitor mixer?

Do the meters reflect the same thing you’re hearing? In other words if you assign an input to, for instance, PGM 3, can you see activity on the PGM 3 meter but just not hear it, or does meter 3 show no activity and instead meter 2 shows activity?

If you assign to PGM 3-8 can you get signal at the appropriate out at the PGM OUT jack or does everything come out PGM 1-2?

 

[fizzicato]

Uh, I'm not sure if I'm explaining myself well. I have a video recording of it, but I can't upload it. Period. Channels 1/2 only receive audio from the rest of the channel asignation bus but they don't receive their own 1/2 bus. They even receive the L/R audio bus send.

 

[sweetbeats]

I understand that implicitly. I’m asking you to do some troubleshooting steps to help narrow down where the issue is occurring. Are you interested in the help? There are multiple ways to monitor the output of the summing busses:

1. Via the monitor buss through the monitor mixer via headphones or at the MONITOR OUT jacks
2. At the PGM OUT jacks
3. Visually via the meters

These various means source signal at different points in the signal path, and if the issue exists in one place and not another then that can help pinpoint where the issue fault exists. Similarly if the issue is present in all these places that also can help steer where the problem is.

You can either help me help you, or I can make a wild-ass guess, which might result in a fruitless goose chase. I prefer the former.

 

[fizzicato]

First of all, thousand of thanks for trying to help me. .

I'll try to explain myself better. The problem occurs during recording, and consequently, also when monitoring tracks 1 and 2.


What happens is that tracks 1 and 2 record any assignment coming from the rest of the tracks, and even the L/R output assignment, but they don't record their own assignment. The strange thing is that they record a sum of all of them. Therefore, if I were to record in complete silence, tracks 1 and 2 would end up with a huge amount of residual noise from the other tracks. In contrast, the other tracks remain silent because each one receives the correct signal it's supposed to receive.


My feeling is that when recording, tracks 1 and 2 are receiving a massive signal bleed from all the other tracks except their own

 

[sweetbeats]

Thanks for the additional explanation.

I still need to know the answers to my previous questions though. Forget recording, and just tell me what happens when you are monitoring an input signal and you assign it to, say, PGM 3. What do the meters show, is signal coming out the PGM OUT jacks correctly or not, and what do you hear in the monitor path.

 

[fizzicato]

Hey @sweetbeats just wanted to update you—the issue is officially solved! For some strange reason, all I had to do was pull out the Rec/Play PCB card, give it a good clean, reseat it back into place, and now the monitoring on track 2 works perfectly. Thanks for the help!

 

[fizzicato]

By the way, there is one more issue I’m having with this 388. Channel 2 only outputs sound—both in monitoring and tape playback—when I turn the PAN knob fully to the right. As soon as I move it even slightly to the left, the sound completely drops out.

I already pulled the channel strip module out, cleaned the pan pot thoroughly, and it didn't change anything. I also carefully cleaned all the switches, but still nothing. Could it be a faulty op-amp or one of the ICs on the channel board? I swapped the card with channel 1, and the exact same issue moved to channel 1, so it is 100% an issue on this specific module's PCB.

 

[sweetbeats]

If you were having such an unusual issue that was largely resolved just by reseating a rec/play amp card, I’d say it’s time to get some DeoxIT D5 and treat and exercise and reseat all the plugin card connections.

And in your last paragraph you said you swapped input channel cards and the issue moved to channel 1 (from channel 2, yes?). There are no amplifier stages past the pan pot; signal goes straight from the outputs of the pan pot to the buss assign switches and then to the outputs of the card. So it’s likely a mechanical failure on the card or the buss PCB, like a bad solder joint. If you have a multimeter you can check the card using resistance on the bench. I’m assuming you can’t get signal to go from the card to PGM 1, 3, 5, 7 or the L buss…is that correct? Or is it just no signal to PGM 1?

 

[fizzicato]

Sorry @sweetbeats !!

Okay, I've figured out the problem. It turns out the pan pot is broken. I replaced it with one from another channel and it works perfectly. Do you know where I could find a replacement?

 

[sweetbeats]

I don’t. So it’s looking for spare channels, or spares from the M-300 series consoles have the same pan pot. I have a bunch of them but they are not center detented, otherwise it’s the same footprint, shaft type and taper and resistance. It just wouldn’t match the rest of them having no center detent.

 

[fizzicato]

The backplate is broken. Do you think I could use the rest of the potentiometer and replace it with a backplate from one of yours? Thanks!

 

[sweetbeats]

What’s the backplate?

 

[fizzicato]

I'm referring to the plate with the potentiometer, the one on the back. The one with the carbon horseshoe. I think I can transfer it to my pot. Would you sell me one?

 

[sweetbeats]

Okay that “horseshoe” is called the element, and the “plate” it’s on or board is called the element board. Yeah you can try that, but it’s not for the meek. You’ll have to bend the tangs that fix the metal pot body to the main chassis of the pot, the cast aluminum part through which the shaft passes…so you’ll bend those 4 tangs out and then the body can be removed, and then you’ll see the end of the shaft in the middle of the bottom and it’s mechanically punched to deform it so it is swedged against the components at the bottom…using a combination of drilling out the end of the shaft and trying to pinch it with pliers so stuff can be slid off the end. And then when you swap stuff out you have to try to recreate the swedge using a punch and maybe some superglue. It’s a real PITA and while you may get a functioning pot, it never feels quite the same again. This is assuming you don’t damage other stuff in the process. I’ve done this a couple times over the past couple decades for situations of true rarity and desperation (like for a couple pots on my prototype Tascam console that were specifically made by ALPS for that one-off console, parts I will never find anywhere else).

 

[fizzicato]

I'll take that risk. It's a shame to ruin an entire channel just for the pan potentiometer. How do we do it?

 

[sweetbeats]

Or you just have one channel that doesn’t have a center detent on the pan pot. Up until the generation of consoles that includes the 388, M-200 and M-300 series consoles, all of Teac’s mixing consoles had pan controls without center detent. But I get it…I’d be bugged by the mismatch too.

Send me a PM so we can connect and discuss further offline.

Another option is you could get two of the non-center detent pots so if you are unsuccessful and irreparably kill your original pot and the replacement you’ve still got a good whole replacement to throw on that channel, albeit non-detent type. I experimented on and ended up killing 3-4 non-valuable spare pots before figuring out how to disassemble them without killing them when I did the swaps for my prototype console, so it’s not for the meek.