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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 6th Jul 2022, 12:59 am   #1
ricard
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Default Revox B77 remote control dummy plug?

Does the B77 require a dummy plug to operate correctly without the remote, as the A77 does? I was trying out a B77 belonging to a friend of mine, and the transport controls wouldn't latch, so I got out a dummy plug for an A77 (pins 1 and 2 in the connected bridged), and the machine worked, except pause and ff seemed identical and slightly odd in function: when depressed, the tape would pause if in play mode, and when released, it would start to wind.

Later upon looking at the schematics for the B77 remote, it seems all transport control (stop, play, rec, ff, rew) buttons have contacts that make when depressed, so no dummy plug should be needed. The wiring is also different from the A77, which explains why ff and pause behaved identically; they are connected to pins 1 and 2, respectively, so when plugging in the A77 dummy plug, which shorts these pins, one is effectively connecting ff to pause.

Yet the machine will not latch the transport functions without the dummy plug. So does this machine require a dummy plug, and how should it be wired (I would think the Internet would be overflowing with this information, but alas not)?
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Old 6th Jul 2022, 4:36 am   #2
TIMTAPE
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Default Re: Revox B77 remote control dummy plug?

As I recall the B77 doesnt require it.
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Old 6th Jul 2022, 4:47 am   #3
Ted Kendall
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Default Re: Revox B77 remote control dummy plug?

Agreed. The A77 does, though. Something is amiss.
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Old 6th Jul 2022, 6:37 am   #4
ricard
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Default Re: Revox B77 remote control dummy plug?

Thanks for the confirmation!

This should prove an interesting fault to fix. On the face of it, jumpering ff and pause should have no effect unless those buttons are pressed, as all button inputs are pulled down using pull-down resistors. I'll have to have a closer look; right now my suspicion is with 74LS02 on the logic board, or Q17, or the pulldown/current limiting resistors and associated capacitors.

(This is an MkII by the way, so the logic board has a couple of (LS)TTL logic chips feeding a bipolar PROM which provides the actual logic function. Since the control logic itself seems fine, I'm suspecting something around the TTL chips. We shall see...)

Last edited by ricard; 6th Jul 2022 at 6:43 am. Reason: It's an MkII
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Old 3rd Aug 2022, 3:20 pm   #5
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Default Re: Revox B77 remote control dummy plug?

For completeness: The problem with the non-latching functions was that the cue lever (or whatever its proper name is) just below the heads was in the (left) position which inhibits the tape lifter and hence the tape is against the heads at all times. In this mode, the rewind and fast forward buttons don't latch, probably to avoid the unaware wearing out the heads prematurely by fast winding across them. Pressing play restores the cue lever to its normal position, and subsequent fast wind operations then behave normally.

All this would probably have been quickly revealed had the manual been consulted beforehand...
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