Revox B77 problems

[erdebear]

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.

 

[Netlist]

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

/Hugo

 

[Cobra2]

Manual...

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

I have it!

Arne K

 

[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.

 

[Elso Kwak]

Re: Manual...

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

I have it!

Arne K

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]

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]

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]

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]

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]

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

 

[Netlist]

As well as all the radial Frako capacitors. The axial ones seem to be in better condition as is my experience with all axials, regardless the brand. There are also tons of tantalum's to check, so I'll be busy for quite some time...

/Hugo

 

[josephthomas]

Ii have a revox a77mark 1, when on playing mode, the speed runs too fast, also when switching between 7 1/2 to 3 3/4, the casptain motor speed doesnt change . without ic in speedcontrollboard

 

[jsantoro]

Check to see if the wiper of pot on the capstan board fell off. the pots on these machine tend to break if you look at them wrong.
Check the frequency coming off the capstan encoder, should be 1600hz at 7.5 and 800hz at 3.

 

[dotneck335]

Lots of ReVox experts here:
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