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-   -   Revox B77 Mk I - Capstan Motor not revolving (https://www.vintage-radio.net/forum/showthread.php?t=153696)

Bogalousa 3rd Feb 2019 1:46 am

Revox B77 Mk I - Capstan Motor not revolving
 
I have a Revox B77 Mk. I.

I have recently re-capped the power supply module, the power supply board, complete, removed all the Frako caps and replaced them. Replaced the cap in the power inlet area (black connection box with voltage selector in).

I am getting 21V and 24V out of the power supply.

I have replaced the offending 0.47uf cap on all the capstan boards that I own. It was the first component that I replaced. I have three of these Capstan Speed Boards, all working.

The problem may be with the tape transport board 1.177.315-12. I have replaced all the caps, tested the voltage regulators and the transistors, and all seems in order. So the chief suspect seems to be the M7803 24-pin large IC on this board. (IC-4 I think). To replace this chip is about 100.00, of which I am loathed to spend this money on the board. But then I can't guarantee that this will fix the fault and the capstan to start normal operation of revolving.

As expected, the machine does everything else, except it won't record or play. (Well if the capstan motor is not turning, I'm not surprised).

At the moment I am trying to beg, borrow or steal a spare tape transport board to try to narrow down the fault. I also have been told, that if I obtain a later TTB, that I will have to install, between P1 and P2 pins a 8k2 resistor,
as the MkI machine, does not have violet and orange cable to attach to P1 & P2 on the later tape transport boards.

I am trying to cover every eventuality in trying to cure this fault, so if I have missed or overlooked something important, then maybe some kind, tecchie in your forum, might point me in the right direction, in the pursuit of curing this fault. In all other aspects, this machine is operating normally in every other function.

Thanking you for all your help,

Bogalousa :wall:


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