Tascam 388 No Sound.

B

bobob

New member
Hi all,

I pulled my 388 out of storage last week. Was working great, but now it's not. The faders were a bit sticky, so I decided to give them and the pots some deoxit, and give it a bit of a clean inside while was at it.

Since putting all the cards back in, I'm getting no sound at all. When I turn it on, the VU meters jump, in pairs one after the other, along the 8 channels. If I then arm record, or switch to remix, VU 8 jumps, but the rest are stationary.

Tried playing back tapes, plugin a mic in, recording. Nothing. Got a feeling it's something to do with the master channel card, but I've reflowed the solder, made sure everything plugged in right, but no joy.

Anyone got any ideas where I should be looking? Hoping the VU meter jumping one after the other on startup might give someone a clue.
 
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Sucks to be you. I hate big global weird problems like that, especially on something like the 388. This is why it’s super important to take GREAT care and approach working on such devices with methodology and patience. Double and triple check and verify connections when reassembling, make sure the device is fully powered down before disassembly (and remember caps can hold charge for days), take picture, notes, video as you disassemble, get a bunch of baggies and label parts in bags…you may have done all of that and I’m not trying to be judgmental, but the smallest act of carelessness can have tragic results. I’ll reiterate my story where I completely roached a mint condition Tascam 58-OB I got for $125…re-inserted an amp card offset by one pin on the card edge connector. Too bad the design allowed that to occur…but I did it…took out the power supply and multiple assemblies and components downstream from the power supply, including multiple components in the transport servo tensioning system. One pin.

Your issue sounds a bit scary to me, it’s global but complex, seems to be effecting all systems. Does the transport function? And just to verify, what happens if you plug a mic into any open input strip, and monitor the ACCESS SEND jack? Do you have any signal there?

Another thing to check, it is unfortunately really easy to bend pins when re-inserting cards in the cardbay, especially the right-hand bay with the bias amp cards, reel servo card and power supply. Pull the power supply out and get a good bright flashlight, look down in the and verify all the pins for the power supply assembly on the motherboard are straight and intact.

You have to be careful when pulling and installing cards on the 388…have to be careful the card is correctly aligned before pressing into place, and even look with a flashlight to verify no pins are incorrectly staged in their socket opening prior to fully inserting the card.
 
Definitely sucks to be me right now. What a nightmare. Can imagine the 58-OB was brutal, you manage to get it going again?

I've had it in pieces this morning, pins are all ok, couple of jumper wires were hanging on by a thread, so sorted them. Put it back together, still nothing.

The transport and tape are working as expected. Just nothing coming in or out of the mixer. Tried the access send jack, still nothing. When the VU's are jumping, there's nothing to be heard out of the mains or the headphones.

Thinking it might be something to do with the master channel card, as when I push any of the buttons on it, VU 8 jumps. Doesn't with any of the other strips, apart from if I switch to remix on 7 or 8. Sorry if this is a dumb question, but what purpose does the buss board on the back of the channel cards have? What signal is it sending? Is it just power?

Will keep at it but man, really weird. Almost as if there's a short somewhere, but cannot see one for the life of me. Put a video below to show what's happening when firing it up. So annoying that it was working fine and simply cleaning it has broke something! Starting to remember why it went into storage...

 
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I couldn’t fix the 58…it was way over my head…sold it for pennies to a friend who had the wherewithal to fix it. And he did.

I wouldn’t assume “just cleaning” is the cause of your current maladies with your 388. Something is incorrectly connected, or there is a bad solder joint or joints now, etc.

When you ask about the buss board on the “back” of the channel cards are you talking about the long PCB that spans across the *bottom* of the mixer cards? If so that’s the buss PCB, and handles all signal propagation for all busses…like, all of them…and the solo and L-R buss control signals, and yes all the power and signal grounding as well. Everything.

You’re really focused on the MONITOR PCB (what you’re calling the master channel card)…sure, you may be right, maybe the fault is there, and you can go stabbing around there and see if you can find something wrong, but at this point you’ve got a global audio failure. If you can’t even get signal from a mic to the ACCESS SEND jack, you need to start at the headwaters and make sure your power supply is working. If it was me I’d start by tipping the machine on its side with the bottom panel removed, find the power rail traces on the BUSS PCB, power it up and make sure the +5V, +15V and -15V power rails are actually running at the specified DC voltages, and then also measure for AC volts on each rail. There should be virtually none. What meter are you using? When the shit is plopping off the fan you always start at the headwaters and make sure the power supply is working first.
 
Sorry, you're right. Hoping for an easy fix, will slow it down. Appreciate you helping.

Also thinking it's a connector, but they're pretty hard to put in the wrong spot with the colored molex's. Would not put being absent minded past me though.

Using a Tenma meter. Voltages are:

5 - 4.785
+15 - 14.530
-15 - 0.8612

Guessing that -15 might have something to do with it.
 
What model meter. Telling me the make of the meter isn’t enough.

Yes. The -15V rail is not working, or there is a break in the connection from the output of the power supply.

So now comes the fun part, you get to start at the pins on the motherboard that correspond to the output of the -15V supply and see what you have there. If it is similar to what you measured at the buss PCB then you likely have a power supply repair in your future. If you have appropriate voltages at the PSU output pins on the motherboard then you have to start tracing out where the power goes to identify the failure.

Also, did you measure the AC voltages there at the buss PCB for each power rail? I don’t see that listed above.
 
Hey mate, sorry, it's the Tenma 72-10415. Got a Solartron 7150plus too if more accuracy is needed.

Traced it right back to the power supply board. Components tested fine, so got it back to the fuses, the black line, but no joy after changing them. The black is also not giving a clear reading on AC, jumping and flicking to open line. Not good. Readings from Fuse PCB are:

Orange - 13.47
Blue - 17.86
Blue - 17.86
Purple - 4.734
Black - OL / Jumping.

There is AC on the +15 rail on the buss board, but I can't get a reading, it's jumping. But +15 DC is reading fine. All the other lanes are AC free.
 
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I don’t know what you mean “the black line”.

We’re not interested right now in measuring the output of the main transformer. We’re interested in measuring the outputs of the power supply assembly.

You said you “Traced it right back to the power supply board. Components tested fine…” What does this mean? What components? What did you measure and where did you measure?
 
The black line is the line labelled black from the transformer and fuse assembly, line 8. I measured the power supply assembly and the -15 was reading 0.8 on P5 onwards. So it's right back to the fuses. I thought it might be C116, C122 or R106, but they all test fine.
 
I doubt it’s a failure at the transformer.

But we can check if you think it is.

I think you have a power supply failure.

Remove the power supply PCB.

Set your meter to AC volts.

Switch the 388 on.

Measure AC volts across the orange wires, then the blue wires, then the purple wires on the output or “secondary” side of the main transformer.

Document the results.

Now switch the 388 off.

Plug the power supply PCB back in, switch the 388 back on and do the same measurements for AC volts across the pairs of transformer secondaries. Document the results, and post that all here.
 
I had to step away from it this morning, was making mistakes.

It's not actually pin 4 of P5 on the power supply board and the mother board (2). It's pin 2 that's the problem. Pin 4 is reading -17v.

Traced pin 2 back to P4, which again is giving the low reading. Would I be right in thinking the next place to look is past P8/J8 on the mother (2), to Q1 on the TR pcb?
 
You’re all over the place. I want to help, but it’s hard when you keep jumping around. You’re not going to solve this by putting on a blindfold and throwing darts. Just slow down.

We have data that suggests a problem with your -15V power rail at the end of the BUSS PCB. Let’s wind this back to what I suggested we do next which is to see if that same condition is present at the output of the power supply.

Set your meter to DC volts, and find the solder pads for P5 on the underside of the MOTHER (2) PCB. That’s the motherboard the power supply plugs into, and P5 is the power supply connector that contains the regulated +/-15V audio power rail outputs. Note that the +15V rail on pin 3 is mislabeled on the power supply schematic…it is labeled as “+15V NST” but it should be “+15V STB”.

Now measure between pins 1 and 2 of P5 (pin 1 is the audio rail ground reference, and pin 2 is the -15V rail). Report the results. Next, measure between pins 1 and 3 (which is the +15V rail). Report the results.

Let’s do just that for now.
 
Hey, yeah that's where I'm at.

Pin 4 of P5 is reading 15.885. It was my mistake earlier, was reading the pins the wrong way round.

Pin 2 on P5 is the same reading as the buss, 0.8857. I traced that back to C107 etc, but the components there are testing fine, no blown caps. So then I traced to P4, which comes before the capacitors at C107, and I'm getting the same low reading on pin 4 of P4.
That leads up to Q1, which I haven't tested yet as I haven't had chance.

Results on P5 are:

2 - 0.8857
3 - 14.602
4 - 15.885 (positive)
 
Stop worrying about pin 4. That doesn’t have anything to do with the audio circuitry.

You said pin 1 to pin 2 measured “- 0.8857”. I can’t tell if the “-“ is there as part of the bullet or if that’s negative 0.8857.

Could you not use those symbols unless for denoting positive and negative? Details matter here.

So…is this correct? Because you didn’t use units or note positive or negative (maybe) when reporting what you measured across pins 1 & 2 and pins 1 & 3…so, again, is my translation below accurate to what you measured?

Pins 1 & 2: -0.8857VDC
Pins 1 & 3: +14.602VDC
 
Okay. And then what we’re the results of the AC voltage measurements of the main transformer secondaries? The measurements across the pairs of orange, blue and purple wires?
 
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