Problems with Tascam 38, help needed

  • Thread starter Thread starter WhinyLittleRunt
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WhinyLittleRunt

WhinyLittleRunt

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Hi everyone,
I have posted on some of these issues in the past and have tried repairing my unit a couple of times with no success, but I think I have a better grasp on what's going on now that I have been looking at the schematics and diagrams....

Basically what is happening is no channel will get signal in any of the modes, nor will it play back a previously recorded tape. I have tried direct input/output from the RCAs to make sure it wasn't a mixer issue. I have checked and reseated all fuses and they all look fine (from a visual standpoint; nothing is burned out.)
I also reseated all of the channel cards and really took the time and care to make sure the pins were all contacting perfectly, as well as the master oscillator board and the cables on the top of the channel motherboard.

When I turn the unit on, all of the VU meters jump like they usually do except channel 6 peaks all the way. (I reseated this card with the rest and that didn't change; I did not swap the card yet). So that's one random problem which could be card-related.

-Unit powers on fine
-All motors and transport functions work normal

Where should I start the electrical diagnosis? I want to see if the channel input/output section is really working because that's mainly where the problem seems to be... I'm just a bit bummed I haven't been able to use my machine for a while and now I'm sort of itching to get it going with the new year and all the ideas I've had. Trust me, any help at all would be amazing! I hesitate to bring this somewhere for service because I can do this stuff myself as long as I know where to start. On the other hand, I'm sure it can use a real once-over and calibration...
 
Where to start is with the power supply. If all 8 channels are not giving you any sound on input and output, you have to look at the circuits which are common to all of them. The power supply is one of those common circuits.

And just because the meter's jump when you turn on the deck doesn't mean that they're receiving full and normal power.

Also; Visually checking fuses is not actually checking fuses. Test them out of the circuit for continuity with an ohm meter. Good fuses read zero ohms. And while you're looking at the fuses, make sure they are the correct values according to the service manual. If you bought the machine second hand, you have no way of knowing if the previous owner stuck the wrong sized fuse in there at some point which could cause disastrous damage to the circuits its powering if it can't shut down, (pop a fuse), to protect the deck. Check the value and know for sure. Don't check it at your own peril. Your choice.

The one channel where the meter pegs could mean there's a short in there which may have blown the fuse that you haven't properly checked yet.

If there is a short in there, it will only pop yet another fuse, should you find a bad one. Keep in mind fuses blow for a reason. They don't just blow because of old age.

If you don't know what you're doing, get it fixed professionally. There's no shame in it. :)

Cheers! :)
 
Ok, cool... excellent advice. When I say I visually checked the fuses, I literally pulled them all out one by one and checked to make sure nothing was blown. When you say check with an ohm meter, I don't want to sound stupid but I can use a multimeter set to Ohms, right? :rolleyes:

I should probably move the channel card that is jumping to see if it the problem moves with it also...
 
Ok, I checked some things. Think I'm getting to the root of the issue.

-I moved the offending channel card, problem did not move with it. Stayed on meter 6.
-Checked the fuses. First I checked to make sure they were all the right amperage, which they were but I had swapped one around to see if it would follow that channel, until I realized they were totally different amps. Anyway, I measured the fuse for channel 6 and it was 0.13, while the first 2 were .00 and they progressively started reading 0.02 upward until the 6th fuse, then started dropping back to 0.00. Then I don't know what happened but I blew the 5th fuse somehow. I'm going to run out to Radio Shack and pick up all new fuses and see if that makes a difference...
 
It sounds very much like you have a short circuit somewhere in your 38. Farting around with fuses is not going to remedy the short.

Take the machine in and get it looked at by an experienced technician.

Cheers! :)
 
Thanks... I emailed a local place that supposedly services these, so hopefully I'll get somewhere with them.

In the meantime, I noticed something else after putting it back together... the left reel is not moving now because the spindle itself is pushed back inside the opening somehow... I never took off the front panel so I'm not sure how I could have done this...
 
I was able to figure out why the hub was stuck; I must've laid the machine down on the hubs for a few seconds and it pushed in one of them. Two adjustment screws from the inside fixed that problem.

I replaced the fuse that blew (3amp for channel 6) but my VU meter still pegs and I get no input metering. That particular fuse is measuring out like .18 ohm when everything else is .00 +/- 2 (normal). I want to test the power transformer before going any further. There are no techs in my area that want to look at this thing and I'm reluctant to drive too far for it just yet...

Anyone know how to test the transformer to make sure it's putting out the correct voltage? I mean, which pins on the connectors/whats the voltage supposed to be? I tried the manual but couldn't find that info... just the part number and location...
 
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