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Old 1st Dec 2017, 12:55 pm   #1
shawthing
Retired Dormant Member
 
Join Date: Oct 2005
Location: London, UK.
Posts: 40
Default Revox A700 flutter only at 7.5ips?

Hello all, I hope someone can help with a Revox A700 problem I’ve not seen or heard of before: quite bad flutter but only at 7.5ips .
The machine works perfectly otherwise; it had a comprehensive rebuild about 4-5 years ago as it’s a long-treasured machine - all caps of all types replaced, all small semiconductors replaced, all resistors checked & replaced where necessary, rubber parts replaced, new heads – you get the picture! I mention this only to rule out the usual age-related failures.
Speed lock buttons all light as usual, same time taken to lock for all three speeds, same degree of audible settling of motor whine. Pinch roller pressure and tape tension eliminated by physical test but also because the problem only occurs at one speed: 3.75 and 15 show no Flutter at all, 7.5 is clearly audible. I do have a W&F meter but it’s packed away – currently however the degree of flutter at 7.5 needs no meter to confirm, and I’ve been temporarily testing all three speeds using commercial pre-recorded classical solo piano tapes that I’m very familiar with.
On just one occasion during testing, the machine refused to go into Play at 7.5, tape lifter / pinch roller didn't move up to contact tape, which I'd never had it do before, but only that once so far.
The degree of flutter seems to decrease a little once the machine is fully warmed up but that may be subjective, from listening to it for longer - if I end up having to unearth the W&F meter I'll confirm that of course.
So, my thoughts are either that a component involved only in 7.5 speed control - presumably on the Capstan control board - has gone out of spec (in which case, can anyone who knows these machines well suggest where I should look please?), or that one of the large ICs on the Tape Transport Control board (SC10429 or TCA561) or on the Capstan Control board (TDA1000 or TCA561) is failing? That may not be the end of the world as I think I have spares stored away, but before I start trying to change them (with possible risks there) can anyone please advise whether sudden high flutter only at 7.5 is something that could be expected from one of those ICs failing?
Any help greatly appreciated, Chas

Last edited by shawthing; 1st Dec 2017 at 1:08 pm.
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