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Revox B77 Smoking.

Discussion in 'd.i.y.' started by Isobarik, Feb 11, 2019 at 11:33 AM.

  1. 337alant

    337alant Negatively Biased

    Other problem caps are the Frako electrolytic in Revox and Studer equipment, in its day an excellent cap but 35 years later has a habit of failing short so can cause damage to other components and ICs.
    Tantalum beads can fail short as well
    my studer A810 is full of logic controls and opamps so could do serious damage.
    The little blue phillips lytics usually just go high ESR and way out of spec on value, here is a 47uf cap, now measure 21uf and 11.7ohms ESR taken from my A810

    [​IMG]20180212_151712 by Alan Towell, on Flickr

    Isobarik likes this.
  2. Isobarik

    Isobarik pfm Member

    Hi Alan
    I will eventually recap both of my machines which are a Revox B77 Mk1 and a Revox B77Mk2 the high speed model.
    It's a learning curve for me:confused:. Just looking at the service manuals and trying to understand them at the mo but getting there slowly!
    Thank you so much for your most valuable advise.
    I always take photos for reference, before I undertake working on any piece of Hi-Fi equipment but should note it down too.
    I also need more test equipment as I only have a multimeter at the mo.
    Just waiting for the components to arrive.
    Best regards
    Last edited: Feb 12, 2019 at 7:22 PM
  3. mikemusic

    mikemusic pfm Member

    Thanks guys
    One of my B77s smokes
    The other needs the pinch roller replaced as it melted.
    Must take hand from bottom and get them fixed
    Thanks for the contacts
  4. Tony L

    Tony L Administrator

    At the least you could swap the good pinch-roller onto the non-smoking one!
  5. Isobarik

    Isobarik pfm Member

    Hi Mike
    Have you still got the Pinch Roller Hub? If you have, have a look at this!https://www.ebay.co.uk/itm/Replacem...n-Revox-Studer-Pinch-Roller-hubs/332991542951
    I've ordered one as the pinch roller on the Revox I've just bought perished, due to the guy being a heavy smoker 'no pun intended'!.
    mikemusic likes this.
  6. 337alant

    337alant Negatively Biased

    Its also worth changing all of the trimpots as they often fall to pieces when you try to adjust them and the contacts can be badly tarnished
    The Piher ones are a very nice replacement , Im not sure of all of the values but I think they are all 10k 250mw check the manual
    here is an example

    Revox online also do them but I can only see them in the kits here

    You will have to re calibrate the machine after replacing the caps and trimpots
    I tend to put the trim pot in the mid position but some people try to replicate the position of the old pot

    To re calibrate you will need a reference tape, signal generator with adjustment on the output level, AC Volt meter (RMS) and an oscilloscope to do it properly

    These are good test tapes and a good price, the MRL ones and much more expensive, I have both and they are within 1dB of each other
    You will need a tape for each speed I am afraid and I am presuming your deck is NAB not IEC equalisation

    Its very rewarding to get these machines sounding at their best again (depending on head wear) you wont be disappointed

    mikemusic likes this.
  7. 337alant

    337alant Negatively Biased

    I have just sent 3 soft rollers off to http://www.terrysrubberrollers.com/ he has a very good reputation over on Tapeheads.net
    They are all from Tascam BR20 R2Rs
    mikemusic likes this.
  8. Isobarik

    Isobarik pfm Member

    Hi Alan.
    Thank you for all the information,much appreciated.
    Whilst the machine is stripped I might as well replace all the caps and trimmer pots as you suggest.
    The Revox i'm restoring use to be mine but sold it to my friend a few years ago. When it left me it was in A1 condition cosmetically and working perfectly, I only sold it to him due to a divorce. He and his mum smoked very heavily hence the state of the machine now.
    It's taken me hours to clean the machine up! Never seen so much nicotine on any piece of Hi-Fi equipment ever! I still have the test tape for the machine.
    I've ordered some power caps to replace the Frako caps that are in place. I've also ordered the three motor run caps.
    Just one small problem is removing the power switch from the facia,it refuses to come off and these small switches are prone to snapping off. Just realised there is no need to remove the toggle switches:rolleyes:

    Thank you for all the links and help.
  9. mikemusic

    mikemusic pfm Member

    Think I had another problem so used a trusty G36 instead
    One day I will have enough time to sort everything, as well as the will power
  10. mikemusic

    mikemusic pfm Member

    Thanks Ray
    Looks like I will be getting one of those soon
    What a common problem this must be.
  11. mikemusic

    mikemusic pfm Member

    Thanks Alan
    Another option.
    Reminds me of when I was in print. Roller recovering could save big money
  12. 337alant

    337alant Negatively Biased

    Mike the picture of the refinished rollers look very good
    Think I will send him my spare Garrard 401 idler wheel

  13. 337alant

    337alant Negatively Biased

    Its certainly worthwhile cleaning all the switches and pots with something like deoxit D5 also where the switch contact the gold pads on the circuit board to the lower from control panel these can be tarnished and noisy
    You will see Christian Rochette doing is about 20mins into this video

  14. Isobarik

    Isobarik pfm Member

    Hi Alan
    Thank you for your link, it's proving to be most helpful. Saved me a lot of time regards stripping the machine.
    Well the Revox is now functioning of a sorts. I replaced all the caps in the power supply including the motor run caps.
    It plays, but having problems with fast forward and reverse, the tape spills when I press stop.
    I tried the machine in the record mode and one of the main fuses blew in the power supply,blowing one of the red record leds ,the other is very dim.
    I replaced the fuse in the power supply and the Revox powered up but still the tape spills.
    I'm going to remove the panel where the input cards are inserted and investigate further.
    Probably a component has failed on one of the boards?
    I have quite a few tapes that I recorded when I first owned the machine and they sound marvellous.
    I will carry on my quest to get the machine working properly.
    I'm working in the dark and as I said, I only have a multimeter as a diagnosis tool but i'm not giving up!
    I don't want to go swopping boards from my other Revox as they are different models and don't want to take the risk of those boards blowing.
    The Revox i'm working on is a Revox B77 Mk2 Nab high speed model, the other machine is a Revox B77Mk1.
    I have checked and double checked the work I have done and all the connections to the boards are correct according to my notes,photos and the manual.
  15. 337alant

    337alant Negatively Biased

    Ray spilling tape is usually the brakes not working
    That could be adjustment of the brakes or a solenoid not actuating the brakes, check the brakes are clean, springs in the correct position solenoid is wired correctly and adjusted correctly. When you press stop have a look and see if a solenoid clicks in
    It also could be associated with tape tension board and I think there is a relay on that board
    Have you recapped all of the plug in boards?
    There could be a shorted cap in the record boards which is stressing your power supply when you put it into record mode

    Double check the polarity of all your caps and dont forget the tantalums are polarised as well
    Check you have all of the wires reconnected to the correct location (check your photos)

  16. Isobarik

    Isobarik pfm Member

    Thank you Alan for all your help.
    I've got the rewind and fast forward working correctly but when I go direct to play, the tape spills.
    I haven't recapped any of the boards as of yet. I'll have a good look tomorrow.

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