Revox A77 HS won't start

F456GTM

VIP/Donor
Oct 21, 2015
110
28
405
Pinecrest, FL
Hello,

My A77 MK III high speed arrived rebuilt from Germany and it is in superb condition.

I had an A77 in 1968 but that was too many years ago, so I do not remember how to operate it properly. The owners manual is poorly written, drawings are not better.

My problem is that when I press the Start button it does not start, is that key supposed to lock? The recorder's capstan shaft is running, the dummy is plugged in, the spooling motors button is ON.

Any ideas?

Best regards,
 

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Tapetech

Well-Known Member
Apr 10, 2014
142
23
328
Fairfax, VA
Make sure the tape you are using is past the leader tape. The deck won't stay in play if leader is under the auto-stop optical sensor.

If not leader tape, then clean the contacts for the dummy plug with Deoxit. And make sure there is a jumper wire installed inside the plug.

If plug is good, then see if all of the spark-suppress caps on the transport relay board have been replaced. They should have been replaced (they have a 99.9% failure rate). If caps are new, then test all diodes on the board with your DMM in "diode" mode. If good, pull and service all of the relays. Use a burnishing tool to clean the contacts and treat with Deoxit after.

Noticed a reel of Ampex 456 tape. Do you know it is defective tape?
 
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F456GTM

VIP/Donor
Oct 21, 2015
110
28
405
Pinecrest, FL
Thanks for the tips.

I have no idea which one is the auto-stop optical sensor. Please see photos.

I have the plug in my hand that came with the recorder, where is the jumper wire?

I bought the 456 it in 1992 in a music shop [Rolls Music] in Falls Church, VA, when I had the Ampex 351, but never used it. I also have a new Quantegy GP9.
 

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Tapetech

Well-Known Member
Apr 10, 2014
142
23
328
Fairfax, VA
Thanks for the tips.

I have no idea which one is the auto-stop optical sensor. Please see photos.

I have the plug in my hand that came with the recorder, where is the jumper wire?

I bought the 456 it in 1992 in a music shop [Rolls Music] in Falls Church, VA, when I had the Ampex 351, but never used it. I also have a new Quantegy GP9.

Sensor is right above light bulb. If you have opaque tape (no leader) then light transmission to the sensor is not the problem.

Yo have to open the plug to see if the jumper wire is soldered in place. Try cleaning the connector.

The spark suppress caps on the relay board are new, so that's not the problem.

All Ampex 456 tape is defective or will become defective. Doesn't matter if you have not used it. Quantegy tape is fine. For new tape, buy RMG SM911.
 

Curt Palme

Well-Known Member
Jan 25, 2012
86
1
83
Sounds like you may have a logic board issue. No offense, but many A77s are not standing up to the test of time, even when rebuilt. Age is simply creeping into these machines, so whenever I sell one, I run the heck out of it, and even then the odd one comes back with some issue. The trimpots go brittle, etc. if you're not a tech, then I'd find one to work on the deck. It sounds like a component failure at this point, not something you've done.

Much Ampex 456 tape does shed, squeal or go sticky, but I've had excellent success with tape baking, which brings them back to life. I've only had one tape (BASF, I think) that refused to come back to life after baking many times. It did restore the tape back to playable condition, but it's still shedding. Google 'tape baking', and you'll find out how to do it.
 

microstrip

VIP/Donor
May 30, 2010
20,806
4,698
2,790
Portugal
Does it operate in Fast Forward/Rewind mode?
 

F456GTM

VIP/Donor
Oct 21, 2015
110
28
405
Pinecrest, FL
The machine has been completely rebuilt in Germany. So when I took off the wood case to check the fuses on the power supply board I found that two of the transport relays had come out of their sockets. According to Tapetech the rebuilder neglected to use the wire hold-down clamps for the relays. It works fine.

Thanks for the interest.
 

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