Tascam 34 - meters doing strange things

  • Thread starter Thread starter rob aylestone
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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.
 
I agree. I just have to find them and, if there is no no DC, figure out why.
 
That’s the operation manual, not the service manual. No useful info in there, got it already.
 
frnkfrkl said:
That’s the operation manual, not the service manual. No useful info in there, got it already.
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Um, no? 106 pages? Full service instructions, theory of operation, exploded views, PCB layouts, schematics…it’s the full operation and maintenance manual…all the info is there regarding where the power supply is located and the wiring diagram…take a look…If that’s what you have and it’s not helpful there’s no document more helpful. I don’t have time at the moment to walk you through all of it…maybe soon, but you should try on your own first…I’ll check back when I can.
 
Look at page 82 of the service manual linked above…that’s exploded view 4. Looks like the power supply PCB is horizontally mounted below the reel motors and above the motherboard. Looking further on page 105 we have the schematic that includes the power supply. We can see the power supply outputs connect to the motherboard via a white 11-pin connector J171. The +/-15V rails are on pins 9&10; 0V reference is pin 11. Unplug J171 from the motherboard. Measure for DC volts across pins 10&11 and 9&11.
 
Hmm. I’ve got one with the same cover photo and it’s strictly an operations manual…something fishy here….
 
sweetbeats said:
Look at page 82 of the service manual linked above…that’s exploded view 4. Looks like the power supply PCB is horizontally mounted below the reel motors and above the motherboard. Looking further on page 105 we have the schematic that includes the power supply. We can see the power supply outputs connect to the motherboard via a white 11-pin connector J171. The +/-15V rails are on pins 9&10; 0V reference is pin 11. Unplug J171 from the motherboard. Measure for DC volts across pins 10&11 and 9&11.
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Beautiful! Thanks. I know where that is. Great help.
 
frnkfrkl said:
Beautiful! Thanks. I know where that is. Great help.
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OK. I'm reading about 6v there. Not 15v. Wait a second.....plugged it back in...... I've got meters and sound from the headphone amp! You nailed it! I've got some intermittent bad connection there, surely. Man, you're a lifesaver! Now the question is: Do I just put it back together as-is or do I pull the motherboard again to inspect the other side for more wonky solder joints? I don't want to pull the motherboard again. It's a pain and who knows what I might mess up on it, just doing that. I already reflowed EVERY solder joint on there.

I had an A 3440 at one time and IT was built like a tank. Same for my 80-8, it never gave me the misery that this machine has. Well, now I know where the (solved?) problem is. I think I'm just going to clean the pins and connector with isopropyl, make sure they're tight and hope that it stays fixed. And if it goes south again, well, I know what I have to do then. Again, a million thanks.
 
Simply "reflowing" suspect joints can often not work. The original problem can be a dirty pin which never 'tinned' properly and you need to de solder it and clean it. I do understand that that would be a mammoth task for all those joints but you may have narrowed the offender down? Remove the plug again and de solder each pin in turn. Put a magnifier on the pin and check it is tinned. Rinse and repeat. Molex plugs can also be a bind. Remove each contact, you will need a 'tool' a large darning needle will serve. Then gently squeeze the side contacts together. Replace and move on.

I had to do this for EVERY CONTACT on EVERY MOLEX plug in an Series One 200 Blackstar amp so no wimpering!

I have a 3340 HS I want to sell but me here. You there!
Dave.
 
ecc83 said:
Simply "reflowing" suspect joints can often not work. The original problem can be a dirty pin which never 'tinned' properly and you need to de solder it and clean it. I do understand that that would be a mammoth task for all those joints but you may have narrowed the offender down? Remove the plug again and de solder each pin in turn. Put a magnifier on the pin and check it is tinned. Rinse and repeat. Molex plugs can also be a bind. Remove each contact, you will need a 'tool' a large darning needle will serve. Then gently squeeze the side contacts together. Replace and move on.

I had to do this for EVERY CONTACT on EVERY MOLEX plug in an Series One 200 Blackstar amp so no wimpering!

I have a 3340 HS I want to sell but me here. You there!
Dave.
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No, heavens, no. I do not need another muti-track tape deck. I'm just transferring tapes to digital (30+ years of tapes) and, when I'm done I'll be selling mine.

I actually sanded the pins with 600 grit sandpaper and then cleaned the schmutz and dust with isopropyl and than spritzed some contact cleaner on them.

Aside: You chose to work on a Blackstar so no whimpering, either. That's one amp manufacturer that I would neither buy nor want to work on.
 
"

"Aside: You chose to work on a Blackstar so no whimpering, either. That's one amp manufacturer that I would neither buy nor want to work on."

Well, when one is employed it is not really "choice"! What have you got against Blackstar? You may not like the S Ones' but they make a vast range of designs and types. What could POSSIBLY offend you about an Artisan 15 or 30?

Dave.
 
ecc83 said:
"

"Aside: You chose to work on a Blackstar so no whimpering, either. That's one amp manufacturer that I would neither buy nor want to work on."

Well, when one is employed it is not really "choice"! What have you got against Blackstar? You may not like the S Ones' but they make a vast range of designs and types. What could POSSIBLY offend you about an Artisan 15 or 30?

Dave.
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I had one once. I don't remember the model. It was cheap because I was broke and had to gig with something I could afford.. Something went south and I opened it up to take a look and it looked like it was built like a cell phone. The choice was to source a board and replace it or just write it off. There's was some sort of problem with sourcing a board as well because the board had been updated or something and something else would have to have been done to make it work. I realised right off the bat that this was not something I was going to do myself so the tech I took it to gave me this info. Board + labour was just not viable so I gave it to a friend to tinker with. Lost touch with him, end of story. That experience rather soured me on Blackstar amps. It wasn't that old, either. I admit that I have not kept up with what they're doing now (I stopped touring about 7 years ago, I'm 64) but that one experience was enough for me to stay away from them. Best sounding guitar amp I ever had was a blackface Fender Bassman. It was stolen. Sigh.
 
frnkfrkl said:
I had one once. I don't remember the model. It was cheap because I was broke and had to gig with something I could afford.. Something went south and I opened it up to take a look and it looked like it was built like a cell phone. The choice was to source a board and replace it or just write it off. There's was some sort of problem with sourcing a board as well because the board had been updated or something and something else would have to have been done to make it work. I realised right off the bat that this was not something I was going to do myself so the tech I took it to gave me this info. Board + labour was just not viable so I gave it to a friend to tinker with. Lost touch with him, end of story. That experience rather soured me on Blackstar amps. It wasn't that old, either. I admit that I have not kept up with what they're doing now (I stopped touring about 7 years ago, I'm 64) but that one experience was enough for me to stay away from them. Best sounding guitar amp I ever had was a blackface Fender Bassman. It was stolen. Sigh.
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Well yes some models are built to 'mid price' levels and servicing almost anything is a trial these days (there orta be a law!) but as I say, Blackstar have a vast range up to the all valve Artisans, totally classic turret board construction and chunky transformers. Not cheap but nowhere near the price of your 'Booteek hand wired' amps.

It is indeed a 'hybrid' amp but all the "tone" comes from valves in the HT-5 and I defy you to find a more versatile 'studio' combo? 5 watts clean but can kick up to 10W of grunge...people can and do gig them with a sane drummer.

(Off topic or WHAT!!)
Dave.
 
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