JVC 3 head audio cassette deck play speed varying.

[Dan]

I have JVC TD-V1050 3 head cassette deck, a high quality unit originally
costing about $500. On playback, the tape now plays too fast, the speed
fluctuating slightly but never going down to or below normal playback speed.
I assume this is a problem with the signal/circuitry that regulates the
speed of the direct drive pulsed servo capstan motor. I have no service
data on the machine, not even a schematic. If anyone can tell me where I
might get service literature, or if anyone has any idea what the exact
trouble might be (i.e., if you've come across this before) please let me
know.

Thanks,

Dan

 

[Alan Peterman]

It's almost certainly a problem with a worn or hardened pinch roller. The pinch
roller is not pressing the tape against the capstan well enough, so the take up
reel torque is pulling the tape through FASTER and with variance than the
capstan speed. Either replace or renew the pinch roller rubber and your problem
will likely go away.

Of course it could be in the capstan motor speed, but the probability if the
pinch roller has not been serviced would tend to implicate the later as opposed
to the former. Sorry for the lawyer lingo - something took over my keyboard!

 

[Dan]

Alan-Thanks for the reply. I have tried cleaning the rollers w/alcohol
(they were fairly glazed) and also pressing them a bit more tightly against
the capstans, but the problem really doesn't change (if I press hard enough
the tape will stop completely, but that's as close as I get to slowing to
normal speed). Interestingly, if I stop the take-up reel momentarily,
(which should eliminate what would be pulling the tape too fast, I'm
thinking) again there is no change. Any further ideas? I really wish I
could get some service lit. I've been away from this stuff for some time;
does Sams still make service literature for equipment like this? This would
have been a fairly low production unit. I wonder where I could get new
pinch rollers? I doubt MCM would have them... If I had some idea
where/what to look for in terms of waveforms etc to the servo motor I could
maybe see if that was the trouble.

Thanks!

Dan

 

[Alan Peterman]

Alan-Thanks for the reply. I have tried cleaning the rollers w/alcohol
(they were fairly glazed) and also pressing them a bit more tightly against
the capstans, but the problem really doesn't change (if I press hard enough
the tape will stop completely, but that's as close as I get to slowing to
normal speed). Interestingly, if I stop the take-up reel momentarily,
(which should eliminate what would be pulling the tape too fast, I'm
thinking) again there is no change. Any further ideas?

I usually recommend against using alcohol on rubber parts - it dries them out.
There are some good rubber renewal chemicals that make it soft and sticky again,
but if taking the tension off the take up reel does not change the speed, you
may well be right that the problem is in the capstan drive system.

I see that the service manual IS available on line at:

http://www.treasurechestcorp.com/JVC.sm.audio.html

Of course they get $16 for it, but that may be a fair deal if your time is worth
anything!

 

[Mark D. Zacharias]

I think I would investigate the area of the capstan motor (it's associated
pc board, if any) and at the main board looking for bad solder connections.
Had one like that recently, though not a JVC.

Mark Z.

 

[Mark D. Zacharias]

P.S.

Don't ignore the possibility that the cap motor may need cleaning and
lubrication after all these years - though it doesn't really seem to relate
to your immediate problem.

mz

 

[Dan]

Thanks Mark, I am looking at that area right now. 1st thing I've noticed is
that some of the oil from the motor has leaked out onto the small pc board
on which it's mounted & actually eaten away a bit of the coating, turning an
area of trace black! Don't think it's corroded through, but there's quite a
puddle of it around the leads of several components, conceivably causing
some unintended paths.

Dan

 

[Mark D. Zacharias]

I wonder if it could be capacitor leakage. Lubricating oil isn't corrosive
in my experience. Cap leakage is notorious for causing unusual problems in
electronic circuits.

mz

 

[Dan]

Mark-You were exactly right, it was in fact 2 leaking caps on the motor pcb.
I thought it was odd "oil" would corrode as well, but since the liquid was
right next to one of the oiled capstan wheel supports, it's what 1st
occurred to me. I guess I associated leaking electrolytics more with
swelling & oozing crud than the amount of viscous liquid that surrounded
these 2 very small caps. Speed is now ok, however the deck won't RECORD as
a result of the idiotic snapping of that zener, which I am still trying to
ID.

Dan

 

[Mark D. Zacharias]

Cool. I love it when I'm actually right (read: LUCKY) for a change.

Good luck with that zener.

Mark Z.