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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 14th Dec 2022, 11:36 am   #1
jascha
Hexode
 
Join Date: Nov 2005
Location: Kent, UK.
Posts: 332
Default Revox B77 speed issue

Hi,
My B77 developed a fault in that it won’t drop speed from 7.5 ips to 3.75ips when changing speeds. I can hear the change in EQ when changing speed but at 3.75ips it carries on playing at 7.5ips. The only way it drops speed if I apply braking force by hand to the supply reel or directly to the capstan motor rotor and then it’s fine. No issues to change speed back to fast. If I switch off the machine whilst at 7.5ips and then change to 3.75ips whilst it’s powered off and switch on again it runs at the correct speed.

I have replaced all the electrolytics on the capstan board and also Q1 just to be safe but the problem persists.

Any ideas what could be the issue here please? I am not suspecting the big cap transistor RCA411 but I did have trouble with these on an A77 once when it just ran out of control. Could this be a contributor to the problem?

Thanks for any help.
Cheers
jascha is offline  
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