Tascam 388 No Sound.

[bobob]

They were with it in. With it out:

Purple: 9.184VAC
Orange: 26.79VAC
Blue: 36.38VAC

 

[sweetbeats]

Okay. In is what I was most interested in.

So I don’t know what tools or capabilities you have at your disposal, but what I would be doing at this point if it was me is pulling the power supply out, connecting it to the motherboard via an extender board or a set of custom extender cables, and starting at the output of the bridge rectifier D105 looking with my scope at the waveform and amplitude there for each output to see if there is a failure with the bridge…looking for disparate waveforms. Then looking at the inputs of the M5230L regulator IC pins 4 & 7 to see if anything looked wonky or disparate with the waveform between each input…then the output, and so on down the line until I found a point where there was a disparity between the two rails. They should look the same only opposite/mirror image throughout the power supply circuit. The point where it becomes something else is the likely point of the failed component.

 

[bobob]

Thanks for your help with this, it's very much appreciated. I got it back to Q100. Swapped it out, and also swapped Q101 while I was there, and we now have correct power.

VU's aren't jumping, sound is passing through, albeit only the right channel (only tested with headphones, so might be ok on main outs, will test as soon as possible), but there are still problems with the mixer.

The stereo left right VU meters are dead. All other VU meters seem to be functioning correctly. Tape is playing back, mic signal is passing through.

Buss PCB is reading as follows:

1: +4.816VDC
2: -0.0017VDC
3: -0.0004VDC
4: G
5: +15.117VDC
6: -15.139VDC
7: G
8: G

edit - info correction

 

[Slouching Raymond]

Thought I'd offer my wisdom:
How about 'elimination'. I'm guessing you cleaned and re-inserted many cards.
What happens if you remove the cards, and check just what's left, like the output of the power supply.
The + and - 15V should look good without the cards.
Then insert them one at a time, and see what happens to the voltages. You could identify which card kills the -15V.

 

[bobob]

Hey mate, thanks. Power's sorted, back to normal.

edit - info correction.

 

[bobob]

Sorry, ignore last post. Mixer channels are functioning fine now.

Left channel is only out in headphones. Stereo signal playing fine through main outs.

VU meters, channels are working perfectly. Stereo VU's are dead. Nothing at all.

 

[bobob]

So, had a look at the meter PCB, I've got serial number 00 on my 388, so a lot of components / connectors are missing. Very hard to read the schematic as stuff doesn't match up. On the meter PCB there's no protection diodes at D301 or D302 on P108, so I imagine it's fried some stuff up there too. I need to make up some cables to be able to test it, but need a break! Will report back.

 

[bobob]

Fixed! The pads had lifted on P117 on the monitor pcb. Still only getting the right channel in the headphones, but think I can figure that out now.

@sweetbeats Thanks so much for your help. No way I could have figured that out / had the confidence to figure that out on my own. Very much appreciated. You've saved another 388 from the void.

 

[sweetbeats]

Fixed! The pads had lifted on P117 on the monitor pcb. Still only getting the right channel in the headphones, but think I can figure that out now.

@sweetbeats Thanks so much for your help. No way I could have figured that out / had the confidence to figure that out on my own. Very much appreciated. You've saved another 388 from the void.

Well that’s great news. Glad I could help. You did all the leg-work, I just helped narrow us in on the target. But you had to get into the nitty gritty and figure out em which part or parts had actually failed. So good job.

For future readers, regarding the meter problem, P117 on the MONITOR AMP PCB is the connector which connects the output of the L/R meter source select switch to the meter amp. So because the pads/traces had lifted, no signal could pass. Good job figuring that out too.

This is a good reminder that it can be a challenge to work on PCB assemblies that are made from the phenolic resin material vs glass fiber. The traces/pads are quicker to lift/separate with heat than glass fiber boards, so it’s often really important to have a good iron and good technique to minimize the amount of time heat is applied. And be prepared to know how to repair damaged traces/pads, because sometimes it happens no matter how good your equipment and skills.

 

[bobob]

Thanks very much, appreciate it. And yeah, on some of these pcb's there's more repairs than traces. Had a lot of work done to it over the years. Seems to be working a treat again now, so back to making music. Thanks again.