Revox B77 problems

erdebear · 20th November 2004, 09:15 PM

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.

Netlist · 20th November 2004, 09:25 PM

I'm not sure what you mean but can you stop the motor by hand with the pinch roller in free run?

/Hugo

Cobra2 · 20th November 2004, 10:20 PM

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

I have it!

Arne K

erdebear · 23rd November 2004, 09:58 PM

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.

Elso Kwak · 29th November 2004, 07:47 AM

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.

John Audio · 11th December 2004, 10:07 PM

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).

anatech · 13th December 2004, 01:55 AM

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

Netlist · 7th October 2005, 10:21 AM

I’m 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 it’s nominal speed. (I’m 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

anatech · 7th October 2005, 11:56 AM

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

Elso Kwak · 8th October 2005, 02:58 PM

Yes those pots are weak and fall apart. Also the tape monitor switch needs cleaning with "snake oil"...

20th November 2004, 09:15 PM	#1
erdebear diyAudio Member Join Date: Nov 2004 Location: Norfolk	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.

20th November 2004, 10:20 PM	#3
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	Manual... Can you take a 6+Mb download in your mail-box? I have it! Arne K __________________ Ars longa, vita brevis

11th December 2004, 10:07 PM	#6
John Audio diyAudio Member Join Date: Mar 2003 Location: Exeter	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). __________________ John Audio

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20th November 2004, 09:25 PM	#2
Netlist diyAudio Moderator Join Date: Jan 2003	I'm not sure what you mean but can you stop the motor by hand with the pinch roller in free run? /Hugo

23rd November 2004, 09:58 PM	#4
erdebear diyAudio Member Join Date: Nov 2004 Location: Norfolk	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.

13th December 2004, 01:55 AM	#7
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

7th October 2005, 10:21 AM	#8
Netlist diyAudio Moderator Join Date: Jan 2003	I’m 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 it’s nominal speed. (I’m 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

7th October 2005, 11:56 AM	#9
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

8th October 2005, 02:58 PM	#10
Elso Kwak Banned Join Date: Dec 2001 Location: Zamboanga, City of Flowers, Mindanao	Yes those pots are weak and fall apart. Also the tape monitor switch needs cleaning with "snake oil"...

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