Revox PR99 mk2 transport logic fault

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EKADEK

Well-known member
Joined
Sep 5, 2005
Messages
140
Location
new zealand
hi everyone.
im having an issue with a revox pr99 mk2. the thing essentially goes ok maybe . except that it wont "latch" into its play mode ...
except when  the tape dump mode is engaged.
so u can only play or record a tape whilst dumping the stuff onto the floor.      perfect!
ive checked transistors/diodes etc and swapped out the electros on the tape drive board. and will also do the fader start / logic board and the main power supply electros.
.im also thinking that the ic 2  (PROM  ns2s12sn) may have lost part of it's programmed memory . gotten  too wasted and lost its marbels maybe .    ive changed the switching ic 74Ls279 that instructs the prom.  dam. no change.
how reliable are these PROM  devices? and what the bejesus does one do if they go bonkers?
and. crikey. these machines are a ratsnest of boards and wiring looms.  essentially simple like a b77 except with a whole bunch of extra circuit boards stuffed and stucked awkwardly into the leftover space . 
twice the machine... but four times the headache to take apart.

please. does anyone out there have any experience of these machines with a similar problem. ?  ive found a couple of mentions on the web talking about other issues with revox transports... hmm .  but not really like this one.  or the threads are just incomplete.  any advice would be much appreciated. ta

 
You are one lucky guy.
2 months ago I had a PR99 with exactly the same fault. It took ages to find
and yes, I thought the PROM, after I changed C14 to 18 inclusive and C8 on the tape drive PCB.
The fault is actually on the Fader Start board, a tantalum capacitor was u/s, I think it was
C4, 10uf. I will check for you, and get back ASAP.
Anyway, 25 working hours to find the fault, cost of new component, 25p.

Frank
 
OK, I've checked.  It is C4 on the Fader Start board. 3.3uf 35v rating. I swapped it for a 4.7u 35v electrolytic.
Hope this helps. Any problems let me know. I have the full service manuals

Frank
 
This is also a similar symptom to a bad EOT sensor circuit.

Working PR99's and B77's will act in 'non-latch play' mode when there's no light, but won't latch into FF or Rewind either.

If you can FF or Rewind, I'd look at what 12Volts suggests.

Keef
 
that tant 3.3uf tantalum on the fader start logic board was indeed leaky as hell. and by the look of the circuit - the leak there 'could' cause erratic stop function goings on.  so  i reckon the fault has been found and cured. ta 12volts . i'll have to confirm that after completing the power supply lectro replacement and reassembling this thing.

and thanks ssl tech . the fast forward rewind functions actually were ok. end of tape sense was also ok. 
 
yep .  the machine functions performed fine...
but with no sound. so ive just traced that fault  thru to another leaking tantalum on the monitor board. in the  circuit that operates an input and output muter relay. it wasnt quite getting switched on enough by the circuit with the leaky cap.
all good now.thanks again for the help.
 

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