Tascam 34 - meters doing strange things

  • Thread starter Thread starter rob aylestone
  • Start date Start date
sweetbeats said:
Sounds like everything audio is out. IIRC the headphone amp has a separate power supply from the main +/-25V audio power rails. Step 1: check the audio power supply.
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Concerning Step 1, Yes, that's what I thought. But where is it? There are bundles of wires bundled to other bundles of wires so tracing from the secondaries of the power transformer is a daunting task. If someone could tell me which pcb has that power rail and where on that pcb (left-right up-down, next to the red connector, etc.) I might find it, that would be really helpful. Perhaps there's just one connector in there where the pins aren't conducting, that seems to be a chronic. problem with this unit which is why I reflowed the entire motherboard. Other than connectors, is there another component that would be primordial in causing this problem? I saw relays mentioned above but I've not seen a single relay on any of the boards that I can see visually at this point of disassembly. Lots of transistors, though. I really just need to narrow the scope of where to look. Thanks and I appreciate any insights / info the community might have about this. As I said before, my competence is limited but I'm not a total dummy and I learn quick.
 
Do you have the service manual? It has pictures that show you were the major assemblies are, and how to access them, and all the pinouts with what is what.
 
". Lots of transistors,....." I don't know the gear at all but I might be able to help if you can post links to schematics?
By "transistors" I assume you mean discrete voltage regulators? These can be tricky beast to fix and whilst many designs were SAID to be short circuit proof many were not and the least slip of the test probe and ANOTHER tip41 and associated components goes in the bin!

If practical I would replace discrete regulators with 337/339 ic reg chips. They are pretty short proofed but don't bet money on it!

Dave.
 
Lots of C1865 transistors. I didn't go through them all to verify the part number on each but they all look identical. I tested a few (in circuit) and they behave as they should. These are on the control pcb-137. I don't know if they are being used for amplification or as relays. It was a sudden failure so I'm thinking there must be one component that just gave up the ghost and I just need to pin it down. I have a service manual ordered and on the way. I was just wondering if and hoping that one of you all had taken a deep dive into this machine and could light my lantern. I'm flying blind for now. I'll just wait for the service manual to show up and go from there. That doesn't mean I'm not open to suggestions, opinions from you all. The more info I can gather, the more likely I'll work this problem through. Thanks again.
 
If you mean the 2SC1865 transistor that comes up as a T03 power transistor and thus could well be used to switch power on and off to various parts of the circuit. I think we need to wait for that manual? Do you have a scanner?

Dave.
 
They are marked c1865 but, yes, same reference apparently. And, yes, I was wondering about that switching function. Since I see no electromagnetic relays anywhere, I was thinking that they were doing the switching. There are no relay-style clicks when changing functions so I am speculating that the c1685s are doing that job.
 
And perhaps one of them is not getting the voltage it needs to “open”. Again, speculation…
 
You have a 34 or a 34B?

The 34B service manual is available online for free in pdf format:

https://elektrotanya.com/tascam_34b_4-track_recorder_106pages_sm.pdf/download.html

I’m not familiar with what all is different between the 34 and 34B.

I don’t think it’s worth your while to hunt for small voltage switching transistors like the 1865.

You have a global issue across all audio systems.

I would set your DMM to Dc voltage and see if you have any power at the output of the regulated +15 and -15 volt audio power rails.
 
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