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Old 20th November 2004, 10:15 PM   #1
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Default Revox b 77 problems

I have a Revox B77. The motor that controls the play function, runs, but when play is engaged, the pinch roller's drag on the capstan, stops the motor running. It also does so when switching from 7.5 ips to 15 ips. Anyone with any knowledge, or Revox service manual etc.
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Old 20th November 2004, 10:25 PM   #2
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I'm not sure what you mean but can you stop the motor by hand with the pinch roller in free run?

/Hugo
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Old 20th November 2004, 11:20 PM   #3
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Default Manual...

Can you take a 6+Mb download in your mail-box?

I have it!

Arne K
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Don't believe everything you think...
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Old 23rd November 2004, 10:58 PM   #4
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When the pinch roller is not engaged, it is possible to stop the motor with my hand, quite easily., it then takes some time to regain speed, it stops all together when the high-speed is selected. The other motors work fine.
I should be able to get 6MB into my mailbox.
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Old 29th November 2004, 08:47 AM   #5
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Default Re: Manual...

Quote:
Originally posted by Cobra2
Can you take a 6+Mb download in your mail-box?

I have it!

Arne K

Quote:
Originally posted by erdebear
When the pinch roller is not engaged, it is possible to stop the motor with my hand, quite easily., it then takes some time to regain speed, it stops all together when the high-speed is selected. The other motors work fine.
I should be able to get 6MB into my mailbox.
Hi erdebear,
I think a bad capstan motor (expensive!) or it's drive circuit,
Is it's powersupply OK?
Check anyway if the tacho-sensor is not too far away from the rims.
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Old 11th December 2004, 11:07 PM   #6
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There is a very good Web site - with all the Revox schematics available:

http://www.schori.info/b200s/smdownload.htm

The text is in German though - but even if you can't translate - you will be able to find the correct diagrams......!

Very unusual to get problems with the motors - it is usually the electronics at fault.

Pleanty of Revox expertise available on the Web (and on this forum probably).
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Old 13th December 2004, 02:55 AM   #7
anatech is offline anatech  Canada
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Hi erdebear,
The grease in the capstan (motor shaft) has become thick and sticky. You need to disassemble it, clean the parts with solvent, and relubricate it. Use a fine oil with NO additives. Do not use too much.
You may find other lubricated parts (pinch roller) in the same situation.
The motor drive circuit is fine but working too hard. Fix the fault.
-Chris
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Old 7th October 2005, 11:21 AM   #8
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Iím in the process of repairing a B77MKII as well with similar problems as the original poster.
Irregular speed and powerless capstan motor. Cleaning the motor was only a part of the solution, it took less time to reach itís nominal speed. (Iím talking about several minutes.) The real culprit was a broken R14 pot (speed adjust on the capstan speed control PCB). It was the third one I replaced and these machines are overcrowded with old warn out pots with fragile tapers. R21 and R37 on the reproduce amplifier PCB were the reason of no output signal when it came in.

/Hugo
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Old 7th October 2005, 12:56 PM   #9
anatech is offline anatech  Canada
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Hi Hugo,
Yup, the wipers on those pots tended to lose tension or just plain fall off. Once you see them in front of you, you remember and just replace the lot.
It escapes me why they used those pots, must have been a cost issue. I've been burned a few times with those.

-Chris
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Old 8th October 2005, 03:58 PM   #10
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Yes those pots are weak and fall apart. Also the tape monitor switch needs cleaning with "snake oil"...
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