Originally Web posted 9 July 1998.
Content last modified Sunday, 17 August 2008 .
External links last verified Sunday, 17 August 2008.

This material was originally written for an audience of experienced audio electronic repair technicians and broadcast engineers. Due to the many emails i have received from folks outside these narrow categories, i have decided to elaborate on some of the answers, and add some very common popular questions and answers, originally omitted because the intended audience already knew about them.

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Gerry Gibbs’ submission to the June 1994 Radio Guide got me thinking… i checked the Comments pages at work in the A-77 manual, and here are:

Revox A-77 Repair Tips

Sonic Purity, former stereo repair technician

Transport functions don’t stay latched - Goes to Stop unless buttons are held

The original dummy plug jumpers pins 1 & 2 with wire, so that the machine can operate normally without an attached remote control. You need to either have a dummy plug inserted, a remote control attached, or somehow have pins 1 & 2 jumped if your plug is missing, and you are not using a remote control.

Thanks to the research of one correspondent, we now all know that you can find more information on the dummy plug pinout and what to do at the Revox A-77 Remote Control Plug Schematic page, part of Obsolete Media’s Tape Deck Remote Control Plugs subsite.

Transport fails to stop automatically when the tape runs out or breaks, otherwise works OK

Machine spills tape stopping from fast winding - Brakes don’t work well

Yes.smiley This is a known design problem with these machines. I usually recommend the following:

“Rocking the reels” is much gentler on tape (much of which is old and brittle now) than just slamming the machine into Stop. This method can also be used on many (not all) older Ampex, Scully, TEAC, Sony, etc. relay-logic machines. Do NOT try this on machines which do this themselves in their logic (soft-touch Tandbergs and 1980s and newer machines [all brands], for example). It is also likely to cause more problems than it solves on machines where the transport is controlled by a mechanical knob, gearshift, or similar item, instead of electrical pushbuttons.

If you really want to improve the brakes:

Capstan has no torque/won’t turn at all, funky audio, assorted weird problems

Thanks to Stereophile Mark, who has offered his help with Revox A77 problems (thanks, Mark!).

Capstan won’t turn at all, or runs at wrong speed (fast or slow)

Both of the above components carry the full capstan motor current and must therefore dissipate heat and thereby are most likely to fail. If the above suggestions do not cure the speed problem(s), keep reading, esp. the capacitors section. Replacing one or both of these components should have no effect on the previously-correct (we hope!) speed adjustments.

Excessive wow & flutter esp. near the end of a reel

Won’t drop out of Play when FFWD engaged

Defeat the A.C. power interlock easily with two 8-32 x 3/4" or 4 X 18mm machine screws. Actually any metal pins around this size should work.

Skews tape at capstan/pinch roller interface

Solenoid pulling problems

Discriminating against flaky capacitors

Pinch roller engages capstan in fast wind modes

Thanks to Jean M. of Belgium

Identifying A77 “Mk.” versions

Thanks to Tom M., though errors are mine

Between 1999 and the present, i have received several requests for service information and/or recommendations for places to take Revox equipment, especially A77 decks, for service. Since many of these email queries have had several points in common, i decided it would save all of us time for me to answer these semi-FAQs here.

Q1. Can you supply me with parts and/or manuals for Revox products?
A1a. No. I have only the manual and parts for an A710 of my own, presently not working, which i hope to someday fix up. I used to work at a stereo repair shop, Resistance Repair, in Berkeley, California, U.S.A. At the time, they had only one manual per model, and a limited supply of the most commonly used Revox parts (since Revox parts have long been VERY expensive, at least in the U.S.). Note that the vast majority of electronic components (diodes, transistors, resistors, capacitors, etc.) are standard items which either themselves or generic substitutes can be obtained from your favorite electronic parts sources. My favorites are the mail order companies Digi-Key, Mouser, MCM, Newark, and others)
A1b. Thanks to one kind reader of this page (Thanks, Reto!), by the simple act of doing a Google search, the following link for Revox A77 documentation has been found:

Please note that most of the actual schematics (and much of the text) i saw were multilingual. English users should have no trouble with most, if not all, these materials. (There used to be other links, now dead. Go directly to the source and do your own web searches if needed for truly current information!)

A1c. Your ship has come in! The Mother Lode has arrived! Thanks to the extreme generosity of Goreski at B.A.S.E./Analog Rules!, there are now free downloads of complete Revox manuals!
Important: Goreski, like me on this site, went to a lot of time and effort to scan, process, post, and host these manuals, which otherwise would be hard to find and/or cost some serious money… and he is offering them for free. The least you can do is send him a Thank You message better would be to offer a small payment to help offset his ongoing hosting costs and reward him for his generosity! Also see the AudioSchematics.com home page if you have made scans of manuals you have, for another way to contribute.
Q2. Who do you recommend for Revox service?
A2a. In the United States of America and Canada:
JM Technical Arts
313 Rembrandt Dr.
Old Hickory, TN 37138

Contact: Jack Clark, 615-754-8323 (voice), 615-754-8314 (fax)
A2b. If you know or strongly suspect that you have an electronic/electrical problem rather than a mechanical problem:
Bay Area Studio Engineering
San Francisco, California
B.A.S.E. does fine work… the issue, as for nearly everyone else, is that Revox-specific parts have been scarce for a long, long time now. Electronic and electrical parts, on the other hand, tend to be more generic and fully satisfactory replacements remain available.
A2c. Elsewhere in the world: I have no reason to doubt the wisdom of Revox themselves. Check their recommendations.
Q3. Can you answer my Revox-related question?
A3. Maybe. So far, there have been few enough of them (thankfully) that i have actually been able to attempt an answer or two. Please keep in mind that no one is paying me to maintain this website, nor answer email, and that i must earn a living in other ways, to the same degree as most of you. You are welcome to ask me a question as long as you understand the following:
  1. I may not have the answer you seek.
  2. I may not reply to your query. I may be too busy, preoccupied, depressed, or have other reasons for not responding. My response time normally varies from very fast (same day) to very slow (three weeks or more), unpredictably. Please do not take a non-response as a personal affront!
  3. My advice, if any, is offered as-is, with no warranty expressed nor implied. It is worth all you paid for it, or less smiley.

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