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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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7th Dec 2018, 11:07 am | #1 |
Hexode
Join Date: Jun 2014
Location: Chelmsford, Essex, UK
Posts: 386
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A77 Speed Issue
Morning all. I have a problem that has developed on one of my A77's. It's a MkIV standard 3.75/7.5ips model. All is fine from startup but after a while, when it's thoroughly warmed up, on 3.75ips it reverts to 7.5ips. If I turn it off for a while and go back later it starts ok then reverts so it's obviously(?) temperature related. The audio quality in and out (when running at the correct speed) is very good. Before I start diving in can anyone point me in the direction to start looking. The machine has been completely recapped on all boards. This appears to be a recent problem (I don't use it all that much now).
Any advice would be most welcome. Mike
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7th Dec 2018, 11:39 am | #2 |
Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,658
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Re: A77 Speed Issue
I'd say around Q203 is where I'd look first - if it's breaking down it will pull the 555 to the slow speed tach frequency.
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8th Dec 2018, 12:43 am | #3 |
Moderator
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,219
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Re: A77 Speed Issue
Try measuring the collector voltage of Q203 at at 3.75 it should be low, see what it is when the fault occurs.
Also measure the voltage at the red wire AE1, this should be 21V at 3.75IPS, Let us know your findings. |
9th Dec 2018, 8:41 pm | #4 |
Hexode
Join Date: Jun 2014
Location: Chelmsford, Essex, UK
Posts: 386
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Re: A77 Speed Issue
Thanks guys, I will do that but not until after Christmas. Will have a bit more time then. It is an odd one though. I’ve had the machine on this afternoon and it plays perfectly at 3.75. I would have thought that it would be well up to temperature by then. It’s not as if it’s dusty internally either, it’s spotless. It’s also not the case that I record a lot at 3.75 but it is handy to record the R3 Throught the Night broadcast direct from the tuner.
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Small Scotch, New Aids and Happy Ears |