[Ian Bell]

Just a quick thank you to all those who suggested possible causes and
remedies for my A77 capstan servo problem (it was running fast on both
speeds). I took out all the 1% caps in the discriminator but even after 40
years they were still within 1%. So, as advised by many, I took out most of
the electrolytics in the circuit and tested them The coupling caps were
good as were all but one of the filter caps - onehad a crack in its body
and measured 0uF instead of 25uF. So I replaced all the electrolytics
except for one for which I did not have the right value. Lo and behold it
runs spot on at both speeds now. So once again, many thanks to all those
who contributed.

A word of warning to anyone else who has trouble this this area of an A77.
All the audio is on easily accessible plug in boards and most of the rest
is fairly easy to get at. The one bit that is really difficult to get at -
so hard you cannot even get a test probe in to check circuit waveforms ,
is - you guessed it - the capstan servo board. You have to disconnect both
reel motors, then unbolt the mains transformer (onto which is mounted the
regulator and servo boards). Even then you need a wooden block on which to
support the transformer while you work on the boards as it is so heavy it
would stretch wires is left unsupported. Not way can you test anything in
this state so you need to find and replace the faulty component, rebuild
and keep your fingers crossed that you fixed the fault.

Needless to say I am one happy bunny.

Cheers

Ian

[hank alrich]

Ian Bell wrote:

Just a quick thank you to all those who suggested possible causes and
remedies for my A77 capstan servo problem (it was running fast on both
speeds). I took out all the 1% caps in the discriminator but even after 40
years they were still within 1%. So, as advised by many, I took out most of
the electrolytics in the circuit and tested them The coupling caps were
good as were all but one of the filter caps - onehad a crack in its body
and measured 0uF instead of 25uF. So I replaced all the electrolytics
except for one for which I did not have the right value. Lo and behold it
runs spot on at both speeds now. So once again, many thanks to all those
who contributed.

A word of warning to anyone else who has trouble this this area of an A77.
All the audio is on easily accessible plug in boards and most of the rest
is fairly easy to get at. The one bit that is really difficult to get at -
so hard you cannot even get a test probe in to check circuit waveforms ,
is - you guessed it - the capstan servo board. You have to disconnect both
reel motors, then unbolt the mains transformer (onto which is mounted the
regulator and servo boards). Even then you need a wooden block on which to
support the transformer while you work on the boards as it is so heavy it
would stretch wires is left unsupported. Not way can you test anything in
this state so you need to find and replace the faulty component, rebuild
and keep your fingers crossed that you fixed the fault.

Needless to say I am one happy bunny.

Cheers

Ian

Congrats, Ian.

--
ha