Time for an update
It has been a good while since I started this thread. This summer I was able to find the time to work on tape decks again, so I pulled all the Revox R2R decks (4 in total) on the bench to see how they do. So here's an update and a puzzle for the PR99.
The B77 deck would not engage play but FF/REW seemed to work fine.
Of the 3 PR99 decks, one has been in regular use and still functioned fine. The second deck had the pinch roller turn into sticky gello, also had ruined reel tables with mangled rods - unsafe to mount reels on them. The third PR99 still had the problem that none of the transport buttons (PLAY/FF/REW) would engage.
I started with the B77, removed the top facia to check inside and also removed the cage from the enclosure.
Tried FF/REW several times with a large reel and without reels. The strange thing I noticed was that during FF the take up spool rotated fast and the left one slower and CCW. However, during REW, the left spool rotated fast and the right one didn't rotate at all.
That could not be a motor fault as it did rotate blazingly fast in FF.
After a few FF/REW cycles I noticed that the right side of the cage was warm, much warmer than the left side. The motor rotor was also hot. I also noticed that when I pressed PLAY without any reels on, the brake solenoid did disengage the brakes and there was a noticeble attemt of the take up spool to rotate and then stopped. Helping the take up spool to start rotating during PLAY did help things a bit but the spool would rotate just a bit and then stop, however the pinch roller solenoid was activated!!!
The fact that there was heat buildup (only noticeable after removing the back cover) made be think: "brakes". I removed the take up reel table and the brake foil and tried again. Bingo! everything did work great. Replaced the reel table without the brake and tried it with tape and it functioned perfectly.
I could not feel anything sticky on the brake pad and the foil was in top condition (clear and without scratches). But it appears the brake pad was actually sticky.
I did have a pair of brake drums available and replaced the sticky one and problem solved. And since I had the take up reel table removed, I replaced the tape counter belt with a new one as it was marginally tight.
Now on to the PR99s that have been idling powered up while I was tinkering with the B77...
First the unit with the gooey pinch roller. Of course I had a couple of spare rollers and that was a quick replacement. I also had a pair of "filthy" scratched reel plates that I had replaced from a deck years ago for cosmetic reasons. Their sprokets however were in perfect condition. On they go.
A few minutes later and that deck was in working condition as well. Threaded a tape and let it run while I would be looking into the "dead" PR99.
Pressed PLAY on the dead PR99 and it engaged. (Shock). Pressed REW and FF and they engaged. Threaded a tape and headphones and it played back nicely. What the heck?
Anyways, I spent some time with the decks and then stopped for the day and switched everything off. Next day I powered up the ex-dead PR99 and tried PLAY (nada), FF (nada), REW (nada)... Short joy! Left it there and started looking for my glasses, came back a couple of minutes later to start the disassembly but pressed PLAY first, it engaged!
Several days later and this deck mostly functions after power up. Sometimes it won't engage the transport immediately after powering up but a few minutes "warm-up" and the transport is functioning again.
OK, there are still some FRAKO caps in there (Tinman, I know the drill - everything strange on a Revox machine with FRAKO caps should be attributed to them without second thoughts).
Will look into replacing the capacitors and report back.
In the meantime, I remember a thread about a VIFA (?) cap exploding on the PSU board of the B77/A77. I can't seem to be able to find it. Can anyone point me to the capacitor in question?
