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Revox B77 Smoking.

Discussion in 'd.i.y.' started by Isobarik, Feb 11, 2019.

  1. Isobarik

    Isobarik pfm Member

    Hello All.
    Bought a second hand Revox B77. I was told it was working correctly but unable to test as he had mislaid the power cord? Anyway got it home found a spare mains cord,switched it on then a puff of smoke appeared coming from the left hand side. A Rifa cap had blown. This one. https://www.vintage-radio.net/forum/attachment.php?attachmentid=150083&d=1506716066 There are no marking left on the cap so no idea which cap to obtain. I think it has to be a X2 type? No idea really.
    Can anyone tell me the type of cap I need? and if possible where to source in the UK.
    I had a browse on the net and it seems that this is a regular occurrence with some Revox tape machines
    Any help would be most appreciated.
  2. madmike

    madmike I feel much better now, I really do...

    A common fault apparently.....
  3. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    You can run it without the cap.

    You will need an X2 cap.

  4. Isobarik

    Isobarik pfm Member

  5. 337alant

    337alant Negatively Biased

    Yes very common fault with the Revox and Studer R2Rs change all with a 275Vac 47nf X2 rated cap. They are spark suppressor across the mains and they usually have some on the motor control boards as well
    IMO all of these old machines need a full recap if it hasent already been done
    The electrolytic capacitors are mainly from Frako and Phillips, the Tantalum caps are also worth changing as mine had really high esr you can change them for electrolytics as well, not sure if the B77 has the non polar Bakelite caps from Roe roederstein as well. The frako and Phillips caps have a reputation for failing short and the Roe caps get leaky crack and dry out. At this age they have also generally drifted out of spec so are worth replacing with good modern alternatives.
    For this I chose the Nichicon Muse KZ, Fine Gold and Bi polar ES series and Panasonic FC.
    I have 2 x PR99s at home and I wont use them until I have recapped them.
    They are good machines to work on though and well worth the effort as they sound superb

  6. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

  7. Isobarik

    Isobarik pfm Member

    Thank you Alan for all the info. I have another B77 so i'll probably recap that too when I've got the smoky one sorted.
    Last edited: Feb 11, 2019
  8. Isobarik

    Isobarik pfm Member

    I'll put an order in this afternoon. Thank you for your assistance Pete.
  9. Barrymagrec

    Barrymagrec pfm Member

    Those Rifa suppression caps are crap - I had one explode out of the vents on my Wolf Ange Grinder.

    I`d be inclined to change any you find.
  10. Isobarik

    Isobarik pfm Member

    Hi Barry
    Yes I've read a few negative reports regarding the Rifa caps. I think i'll get another make. Could you point me in the right direction please!
  11. 337alant

    337alant Negatively Biased

  12. 337alant

    337alant Negatively Biased

    The new ones now are made by Evox -Rifa and I buy them and replace them for the old ones, I have never had a failure of a new one.
    Anything across the mains is subject to surges and spikes so eventually they will fail
    most of those caps are more than 30 years old so its not surprising really

    All my Quad eqipment had the same accross the mains and 2 of them failed as well
    Plenty of different makes out there to chose from
  13. df_genius

    df_genius Solder slinger

    Agreed on the full recap, that includes the motor run capacitors too, and there are more unreliable Rifa caps to replace as well if I remember correctly, not just the mains filter cap.
  14. Tony L

    Tony L Administrator

    The BBC Micro has two of those X2 Rifa suppressor caps in the PSU and likewise they are all but guaranteed to fail with magic smoke and a nasty stench. Just replace them and all is right with the world.
  15. 337alant

    337alant Negatively Biased

  16. Isobarik

    Isobarik pfm Member

    Cheers, Tony.
    I've ordered a couple.
  17. Isobarik

    Isobarik pfm Member

  18. Isobarik

    Isobarik pfm Member

  19. martin clark

    martin clark pinko bodger

    The problem caps are the old Rifa paper-based ones, encapsulated in clear resin: the bond between the resin and the lead-outs can let in enough water vapour over time the dry paper absorbed, that one day, having become 'conductive enough - they let go with a mess. (NB same thing can happen with components in old 'canned' mains filters)

    Modern X1/X2 caps are plastic-film based, and therefore non-hydroscopic - so not going to fail in the same way (and if properly-rated CE/UL etc, not going to fail in any exciting way at all - they'll just lose a bit of capacitance over the next 20-30yrs or so as mains surges slowly eat the self-healing metallisation)
    337alant and Arkless Electronics like this.
  20. Isobarik

    Isobarik pfm Member

    Hi Martin
    Thank you for the explanation, much appreciated.
    Cheers, Ray

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