[help] Trouble with Revox B215 cassette

[SaSi]

After working on a B710MkII with similar problems (after solving the original ones), I re-read the entire thread. And then I had a look at the B215 Service Manual.

I now think I understand the problem, although the SM isn't good enough to help find a solution. (BTW, since the B790 and B77, Revox SM aren't the same quality on newer units).

Anyway, the problem with the 710 was that it would stop FF or REW abruptly and for no reason. This happened after I took out the boards and washed them under running water with shaving foam and a toothbrush.

The end finding was:

There are two pulse signals coming out of the reel plates. Each plate has a photo sensor that creates a frequency proportional to the rotational speed.

The CPU board on the 710 does some work on these two frequencies and then feeds the result to the CPU.

When everything is working ok, FF/REW speed is very fast at the beginning of the tape and then slows down at the end. The End of Tape sensor stops motion as soon as the leader tape is reached.

There are three trimmers on the 710MkII CPU board that adjust this. In a previous posting it was stated that there are more of these on the B215 (but the SM didn't have any details and since I don't have such a deck - sigh - I can't help locating them).

For the 710, one trimmer is used to adjust the sensitivity of each reel plate pulses and the third adjusts the leader tape detection threshold.

When the two reel plate trimmers were off, I had exactly the same problem: FF/REW stopped for no apparent reason while on tape. Adjusting the tape sensor had no effect.

A combined adjustment of the two other trimmers however solved the problem perfectly. While adjusting, I realized that the soap bath wasn't enough so I took out the board again and sprayed a generous amount of Contact clean on the trimmers. There was dirt adhered on the trimmers that soap and the toothbrush didn't remove - it just mis-adjusted them and mixed the dirt.

I'm sorry I can't give any more detailed hints here but I have no clue on the unit's schematics or PCB layout.

 

[Tinman]

SaSi,

Uhhh..... SHAVING FOAM??? THAT'S a new one on me.:scratch2:

I mentioned a small ultrasonic cleaner... try to get one, it'll change your life.

No toothbrush needed. :thmbsp:

 

[SaSi]

Yeah, I like the way it fills up everything. But the toothbrush has been proven to be too intrusive on trimmers. Chemical or ultrasonic cleaning is probably better.

 

[Patlamm]

"He doesn't STOCK rollers, you have to send your old one's in to be rebuilt."

I've sent back an email to Terry and ask if he can rebuild if I send the rollers. We'll see!

I've check the manual, but there's no indication on how to ajust the reels sensor :-( But you think that it can be the problem, right?

 

[SaSi]

I think the deck is using a complicated method of determining if it is close to the end of tape so to slow down. I know it does on the MkII now that it is properly adjusted. It is also checking for acceptable revolutions on the plates so as to cater for broken tape or spools turning but tape not. If I press the cassette sensor and press REW, even masking the tape sensor, it will stop after a few seconds as both reels are turning in opposite directions.

I am confident that on the B215, with 4 CPUs, they have gone even further. I am certain you should first check adjustments before thinking repairs.

BTW, my 710MkII was severely fluttery on occasion during the adjustments. I did fiddle with the pinch roller tension but it didn't really solve it. But once the various adjustments were correct, flutter dissapeared - really.

 

[steerpike2]

>> I've check the manual, but there's no indication on how to ajust the reels sensor

Yes there is. Section 3.2.3. You need an oscilloscope, and adjust for a symmetrical waveform:
MEASURE point - Adjustment point
IC10 pin2 - adjust R15
IC10 pin1 - adjust R16
IC10 pin14 - adjust R17
IC10 pin13 - adjust R18

 

[Patlamm]

Ho ok, thanks steerpike2, i've found it.

 

[Patlamm]

Terry's response:

"Yes I can rebuild them but I don't have the factory spec's for them. If they are about the correct size now, then I can just measure them. If you know what size they should be, that is better yet.

Cost is $35 per roller"

 

[Tinman]

Terry's response:

"Yes I can rebuild them but I don't have the factory spec's for them. If they are about the correct size now, then I can just measure them. If you know what size they should be, that is better yet.

Cost is $35 per roller"

And worth EVERY cent! :thmbsp:

You'll be amazed how they look when they come back.

Marc

 

[Patlamm]

We've check the signal, but it's not conclusive because of the oscilloscope. By the way, i've notice that when I try to do a rewinding, the tape sometimes goes on fast forward by itself for a few moment, then stops. Maybe it can help to find the problem?

 

[SaSi]

Too much forward torque perhaps?

If you press the cassette sense pin (to make it think there is a cassette), do both reel shafts rotate towards their wind direction moderately or does the take up reel rotate too fast?

 

[Patlamm]

They rotate in opposite direction at the same speed.

 

[SaSi]

It appears that the problem you are having is unrelated to pinch rollers. So, even if your pinch rollers need change, they could wait until the problem is solved.

Unfortunatelly, as I don't have a 215, I don't know what you could do, but can only give general ideas based on my experience with the design of the transport:

1. The operation of the transport is depending on what the photo sensor (tape sensor) reads. I was puzzled at some point that I could not achieve proper adjustment and it proved to be that the ambient room light was interfering with the dismantled deck transport. Try doing the adjustments in low light.

2. Even with 3 adjustment trimmers on the 710 (2 for the reel photo sensors and 1 for the end of tape sensor), it proved that the correct adjustment was tricky to achieve and re-adjusting one trimmer changed the "best" setting for the others. I would recommend patience and a good strategy to "study" what each trimmer does and mildly changing it's setting to understand the result. If a trimmer appears to be at an extreme position, it is possible that it is incorrectly set.

3. Try to adjust things that are not depending on others. For example, on the 710, I finally realized that adjusting the end of tape photo sensor should be done first and then bother with the rest.

If you have some good pictures of the adjustment trimmers and perhaps access to a circuit diagram, it would be really helpful to understand what needs to be adjusted first and how.

 

[Tinman]

We've check the signal, but it's not conclusive because of the oscilloscope. By the way, i've notice that when I try to do a rewinding, the tape sometimes goes on fast forward by itself for a few moment, then stops. Maybe it can help to find the problem?

You know, it is POSSIBLE that the entire problem is caused by a dirty commutator in one of the reel motors. If you read my other posts regarding my own B710, I was pulling my hair out until I finally took the motors apart and very carefully cleaned the commutators. Ran properly ever since. I was floored by this, by learned something new.

The Deck senses the current used and CREATED by the motors in order to buck the supply motor to keep tape tension. So my deck would do the fast forward thing, or it would wind a bit while it should have stopped, etc.

The dirty commutator caused the electronics to mis-read the motor and overdrive it.

Really odd design.

Anyway, given the complexity of these decks, I thought I'd throw that one out there again as a possible scenario. That is, once you tried everything else, like I did, and reached the breaking point.

I could have saved myself over 12 hours of troubleshooting had I thought of that one first. Fickle decks!

Marc

 

[Patlamm]

I've made 2 video for ya. On #2, you can see my action at the top right (play, ffw, etc..) You can download them here:
http://www.favreau-audio.ca/B215_video1.zip (6MB)
http://www.favreau-audio.ca/revox_video2.zip (17MB)

 

[SaSi]

OK, your deck appears to show exactly the same symptoms as my 710MkII did. It rewinds "better" at the end of the tape and has more trouble during FF. Also it appears not to sense the end of tape correctly.

On the 710, there are two trimmers on the CPU board that adjust the sensitivity of the two photo transistors sensing the rotational speed of the reels. There is also one more adjusting the end of tape photo sensor. I have no idea where these trimmers are located on the 215.

I first adjusted the end of tape sensor. Find the setting where it doesn't sense the leader tape and then set it a "click" to the correct direction.

Then start with the two photo transistor trimers.

First the Rewind one. At one extreme, it will not do any Rewind. It will stop immediately after pressing Rew. Turn it until you get an improvement but don't turn it more than where it gets barely functional. Rewind a tape fully, even if it takes several pushes of the button. If it is properly adjusted, it will sense the beginning of tape leader tape and stop, engage play, reach the tape and then stop, resetting the counter. Pretty hard to miss.

Then the FF trimmer. Do the same. Don't turn it more than needed, as that appears to mess with the rew setting. If set correctly, it should slow down when the end of tape is reaching and then stop just over the leader tape and not when the reel is empty - stretching the tape.

It took me several FF/REW cycles to get it right and every time only small adjustments were made.

One of the issues were also to identify the proper trimmer for each direction.

But on your deck, it is also an issue to identify where these trimmers are located. On the 710 they are very close to two BD139 TO-220 transistors driving the spool motors - I would guess the 215 uses similar circuitry.

 

[pablopcasso]

Revox B215

The problem is usually the tape leader sensor located between the head and the capstan. Replacing it will usually do the trick. As they are expensive from Studer/Revox, one can obtain them out of any VCR and adapt them to fit. I did and they work like a champ.

 

[Tinman]

The problem is usually the tape leader sensor located between the head and the capstan. Replacing it will usually do the trick. As they are expensive from Studer/Revox, one can obtain them out of any VCR and adapt them to fit. I did and they work like a champ.

Funny you should mention that, I did the same thing. Though I DID have the motor problems to compound things.

Marc

 

[Patlamm]

But I have a signal coming from the tape sensor, i've done the test from the manual. Does it means that the sensor is suppose to work properly?

 

[SaSi]

If you have a signal from the sensor then it works. But the circuit might not be adjusted correctly.