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A repair question

Discussion in 'Electronic Repair Modifications DIY' started by robbiefritz, Apr 9, 2010.

  1. robbiefritz

    robbiefritz Active Member

    Hi. I hope that I am posting this in the correct place. I have a Revox A77 2-track R2R and the other day, a small puff of whitish smoke came from the left lower part of the machine. It continued to play in the short time before I could turn it off and unplug it.

    Any idea what it may be and where to look? Thanks.
  2. TheJackAttack

    TheJackAttack Distinguished Member

    Sounds like you blew a capacitor or similar. Get friendly with your multimeter and a spec sheet if you have one.
  3. dvdhawk

    dvdhawk Well-Known Member

    If you're capable and confident enough to disassemble it without further damage or electrocution....
    *WARNING - leaving it unplugged will reduce but not eliminate the risk of electrical shock.

    There's a chance the part will be visibly scorched, but even before you break out the multimeter .... follow your nose.
    The stench of electronic death will be probably be strong enough to point you to the right general area.
  4. TheJackAttack

    TheJackAttack Distinguished Member

    Wasn't that a band in the 80's? ;-)
  5. Space

    Space Well-Known Member

    Send it back and have it repaired by an authorized tech...don't waste your time learning a new talent.
  6. dvdhawk

    dvdhawk Well-Known Member

    Does that mean the dust mites that live inside have elected a new pope?

    ... but seriously folks....

    Is it possible to send something back to 1967? Revox (Studer / Harman) doesn't seem all that interested in fixing 40 year old tape recorders.

    Space makes a good point, but I'm less concerned with wasting your time, but deadly serious about the risk of electrocution.

    The fact you're here asking is a good thing I suppose, but I'm guessing if you were the multi-meter type you would have had it apart already.

    The bottom line is, is this something that you want fixed right, or something you want fixed cheap, or something you want to take a crack at before you put it in the dumpster?

    If you take it / ship it to someone who does repair work you'd probably have more in the shipping & bench-fee than the parts - guessing by your brief description. Is it worth $50, $100, $150, $200 to you to have it repaired or completely overhauled?

    If you can't justify the expense of having it fixed by a professional, maybe you're thinking you want to see if you can find the problem yourself before you throw it out.
    A) Would you know where to order the replacement part(s) if you identified them? (if the parts are scorched, good luck reading any markings)
    B) Would you be able to desolder the old part(s) and solder in the new part(s)?

    It's a classic, so worst-case-scenario, rather than toss it - I'd eBay it "as-is" to a good home.

    Relevant link to source for service technician & service manuals

    Best of luck.
  7. ampexguy

    ampexguy Active Member

    This is just a guess. Given that the smoke came from the lower left, you may have lost a resistor or capacitor on the "logic" board. This is the one behind the pushbuttons and that has the relays on it.

    Open the machine up (it's fairly simple and obvious and requires only a regular and philips screw driver) and take a real close look at this board in good light.

    The A77 has an interlock that prevents it from being powered up with the cover removed. This can be defeated fairly easily with a pair of screw drivers or banana plugs. Make sure there's no wire connecting the banana plugs to each other. (Guess how I learned that one.) However, you should not have to power up the machine to check what I'm talking about.

    While you're in there, replace all the relays. They are available. If you can't find them & ask nicely, I can probably come up with a source for them.

    People whose opinions I respect have highly recommended JM Technical Arts in Tennessee for Revox A77 repair. However, I have no personal experience with them. When one of mine displayed more or less the same symptoms you're describing, a friend who is a studio tech in NYC took it on and fixed it for me. I know he is not interested in more of that kind of work, though.

    Unlike most of the old analog tape decks that get discussed here, IMHO a Revox A77 *is* worth bringing back to life. They sound good. Though they are not designed to be run 24/7, they are good, solid, reliable machines. I doubt if you could get another deck as good for what fixing yours will cost. Get yours working again and it'll give you many years of service.


    (I think this reply is pretty detailed and knowledgable for an Ampex guy! <VBG>)
  8. Link555

    Link555 Well-Known Member

    Great Response glad to have you with us Ampexguy
  9. robbiefritz

    robbiefritz Active Member

    I appreciate all the responses. They are most helpful. In my opinion, the machine is certainly worth the cost of repair. If it were a capacitor, I could work on that but I guess to some degree I was taking the lazy route of asking the question. Being that the machine is an older one and that many of these electronic pieces from the 70's are having component failures, I figured that some one else may have experienced that same thing.

    Thanks and will reply with what I find.

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