TEAC 80-8 "pops" when punching out

G

gnomepark

New member
Hello,

I have a TEAC 80-8 and when I punch out by either the channel button or just hitting stop, I get a bump or a low end pop that records on the tape.

Does anyone know why this is happening?

Thanks! Mike
 
Could be a couple of things. Does it happen on all channels? Could be a leaky cap in the record amp before the head switch relay. Could be your deck is magged. Do you demag regularly? Could be sync leakage.
 
Another possibility is a failed muting relay. I don't know for sure with the 80-8, but a lot of times there are muting relays that make/break signal continuity before/after and amp is engaged/disengaged to mute that thump.
 
I have just been using it to make copies until now Tried punching in and now this bump.

It happens on all channels. I demag it on a routine basis and everything is clean. Using 911 tape.

What is sync leakage? Are the relay's on each card?

I have another 80-8 I could use for parts as well.

Thanks,
Mike
 
I think what he means by sync leakage is bias signal leaking through when overdubbing. There are bias traps for the record and sync/play tracks.

I don't know where the muting relays would be on an 80-8, or even if there are muting relays. Sometimes transistors are used for this.

Do you have a service manual?
 
sweetbeats said:
I think what he means by sync leakage is bias signal leaking through when overdubbing. There are bias traps for the record and sync/play tracks.

I don't know where the muting relays would be on an 80

Transistors..Yes! The early Japanese kit used really cheap, low hfe devices for muting and they used to fail, often going 1/2 off 1/2 on and noisy.
Replace with BC184L/214L depending upon polarity. There could also be high value base feed Rs, >470k and these can go high/O/C.

Dave.
Click to expand...
 
I'd be surprised if the 80-8 didn't have relays in the signal path. I know the 38 does, and that was the second-generation deck. There was also some rumour that the lead designer quit and went over to Fostex because he wanted to start using solid-state switching in the audio path and TEAC insisted on staying with relays for some reason.
 
jpmorris said:
I'd be surprised if the 80-8 didn't have relays in the signal path. I know the 38 does, and that was the second-generation deck. There was also some rumour that the lead designer quit and went over to Fostex because he wanted to start using solid-state switching in the audio path and TEAC insisted on staying with relays for some reason.
Click to expand...

There's no argument the 80-8 didn't use relays, but we're not talking about signal switching relays, rather muting relays that momentarily cut signal connectivity during function switching to mute any pop or thump.

Looking at the schematics there are muting transistors on each rec/play amp card, but you said the problem is global. All else I can see so far is a power-on muting circuit that would be global...not sure if it may provide muting under other conditions or, if in a failure state, may cause unwanted noise.

On the System Control (Function Select) PCB there is a 2SC1312 transistor associated with the power-on mute circuit Q23. Maybe that's failed? More to know and look at. This is just from skimming the schematics and I'm unfamiliar with the 80-8 in general. You could pull that transistor and test it.
 
Yes I have the manual. I also have a spare 80-8.
Would it be possible to replace out the System Control (Function Select) PCB?
 
Anything is possible. How hairy a job it is I don't know. I don't know where or how that board is mounted and whether or not there is any point-to-point wiring that would need to be removed and resoldered.

I'm not sure I would advise wholesale replacement of entire PCB assemblies just because of a preliminary finding of mine that may have something to do with your problem. I'm not that good. The power-on mute circuit may have nothing to do with your problem, and even if it does Q23 may not be the culprit or even have the possibility of being the culprit. I'm not trying to waste your time by making suggestions, but I also don't want you wasting yours acting on them. I've never even seen an 80-8 in the flesh and never studied the schematics.
 
??? By recording a blank signal through the whole tape and going back and testing again....no bumps on punch in or out....strange... Anyone ever hear of that?
 
gnomepark said:
??? By recording a blank signal through the whole tape and going back and testing again....no bumps on punch in or out....strange... Anyone ever hear of that?
Click to expand...
That can happen on a badly bulk erased tape. Run the tape in wind and listen to the output. If you hear a wopwopwop sound then its badly bulk erased. If you then recorded all the way through, thus cleanly erasing it, the effect will be gone. Effectively a very low frequency mag field gets recorded on the tape, and when you punch in on this you abruptly drop the level at the punch in point. Hence a click.
 
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