revox B77 problems - UK Vintage Radio Repair and Restoration Discussion Forum

dscuddersmith · 23rd May 2011, 3:01 pm

Hi - new here - hope this post is not redundant - couldn't find the info in other posts - so here it goes...

I have a B77 that has worked flawlessly since I purchased it a year ago. The other day the rewind function slowed to the point that I had to finish rewinding by hand. It was a "new" used tape and I thought it might not have spooled up correctly and was causing undue friction and that was the cause of the slowing. I put a tape on that has been played many times and all seemed OK. I bought a motor on eBay - alas, rewind seems to function now, EVEN on the tape that it initially failed on. So it was not the tape, but something internal.
A new problem cropped up over this past weekend - the playback has slowed noticably. The machine is usually run with the speed adjustment off - it can now be run with the adjustment on and turned up to max to get things going at proper speed, although it still sounds a tad slow to my ear.

This is a 110volt machine. Does anyone have any thoughts? I can perform moderate repairs - unsolder/replace/resolder - but do not have an electrical background by any means and am thoroughly confused by electrical meters (the one I have is quite complex which may be half of the problem)...

any suggestions are appreciated.

thanks

david

dscuddersmith · 23rd May 2011, 4:15 pm

Sorry, I reread my post and it is unclear about one thing.

The new motor I just purchased has yet to arrive - in the original post it sounds as if I had already installed it. No repair work has been done to the unit.

Regrets for the confusion.

Mooly · 23rd May 2011, 7:04 pm

This looks quite a fearsome beast... the circuitry, although all "discrete" is very complex.

I think you have to determine if the problem is mechanical or electrical/electronic.

Just some thoughts. The capstan determines playback speed. You have a rewind problem and a playback speed problem... there has to be a common cause.
If you can "spill" some tape of the supply spool and see how it plays back that may help determine if the problem is the capstan running slow or whether there is an excessive back tension or even a brake applied to the supply spool. There may be a "slack" sensor you have to overide to fool it into doing that.

Electronically the first check has to be to confirm all the supplies are present and correct. You'd be surprised how many faults have a simple cause such as supply issues.
The capstan motor on this is electronically governed... it is a very complex arrangement and would require careful and methodical faultfinding and correct interpretation of results.

Perhaps checking the supplies would be a first move... its just you saying your "confused by electrical meters".

There may be a "common" stock fault for this that someone knows however...

Michael Maurice · 23rd May 2011, 10:41 pm

I think the problem could be caused by Sticky Shed Syndrome, this is whre the tape sheds its oxide. There are a number of threads on this subject.

BTW those motors are very sturdy and dont usually fail, though I've had them fail electrically in which case they wont function at all.

TIMTAPE · 24th May 2011, 12:12 am

I agree with Michael. Check the tape path for signs of deposited tape. With the B77 you may need an inspection mirror. Slowing in rewind and then in play are classic signs of SSS. Back coated tapes tend to be the worst.

Tim

paolo · 24th May 2011, 1:22 am

I agree with Michael. This sounds like Sticky Shed. Your "new old tape" is most likely shedding oxide and gumming up the tape path due to the tape binder chemicals breaking down. Before looking for more alarming problems, I recommend you thoroughly clean the tape guide path with isopropyl alcohol and try again with a different tape.

Paul

electroanorak · 24th May 2011, 9:34 am

Hi.

I have had this problem as well. It was the motor run capacitor. These are known to fail as the get older.

Daniel.

djwells01 · 24th May 2011, 1:31 pm

Hi David,

Could you post the make of tape as this could show a leaning towards SSS or that you do have a fault.

Cheers

Duncan

23rd May 2011, 3:01 pm	#1
dscuddersmith Retired Dormant Member Join Date: May 2011 Location: Newtown, Connecticut, USA. Posts: 2	revox B77 problems Hi - new here - hope this post is not redundant - couldn't find the info in other posts - so here it goes... I have a B77 that has worked flawlessly since I purchased it a year ago. The other day the rewind function slowed to the point that I had to finish rewinding by hand. It was a "new" used tape and I thought it might not have spooled up correctly and was causing undue friction and that was the cause of the slowing. I put a tape on that has been played many times and all seemed OK. I bought a motor on eBay - alas, rewind seems to function now, EVEN on the tape that it initially failed on. So it was not the tape, but something internal. A new problem cropped up over this past weekend - the playback has slowed noticably. The machine is usually run with the speed adjustment off - it can now be run with the adjustment on and turned up to max to get things going at proper speed, although it still sounds a tad slow to my ear. This is a 110volt machine. Does anyone have any thoughts? I can perform moderate repairs - unsolder/replace/resolder - but do not have an electrical background by any means and am thoroughly confused by electrical meters (the one I have is quite complex which may be half of the problem)... any suggestions are appreciated. thanks david

23rd May 2011, 4:15 pm	#2
dscuddersmith Retired Dormant Member Join Date: May 2011 Location: Newtown, Connecticut, USA. Posts: 2	Re: revox B77 problems Sorry, I reread my post and it is unclear about one thing. The new motor I just purchased has yet to arrive - in the original post it sounds as if I had already installed it. No repair work has been done to the unit. Regrets for the confusion. Last edited by Brian R Pateman; 23rd May 2011 at 6:12 pm. Reason: (...,.)

23rd May 2011, 7:04 pm	#3
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: revox B77 problems This looks quite a fearsome beast... the circuitry, although all "discrete" is very complex. I think you have to determine if the problem is mechanical or electrical/electronic. Just some thoughts. The capstan determines playback speed. You have a rewind problem and a playback speed problem... there has to be a common cause. If you can "spill" some tape of the supply spool and see how it plays back that may help determine if the problem is the capstan running slow or whether there is an excessive back tension or even a brake applied to the supply spool. There may be a "slack" sensor you have to overide to fool it into doing that. Electronically the first check has to be to confirm all the supplies are present and correct. You'd be surprised how many faults have a simple cause such as supply issues. The capstan motor on this is electronically governed... it is a very complex arrangement and would require careful and methodical faultfinding and correct interpretation of results. Perhaps checking the supplies would be a first move... its just you saying your "confused by electrical meters". There may be a "common" stock fault for this that someone knows however...

23rd May 2011, 10:41 pm	#4
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Re: revox B77 problems I think the problem could be caused by Sticky Shed Syndrome, this is whre the tape sheds its oxide. There are a number of threads on this subject. BTW those motors are very sturdy and dont usually fail, though I've had them fail electrically in which case they wont function at all.

24th May 2011, 12:12 am	#5
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: revox B77 problems I agree with Michael. Check the tape path for signs of deposited tape. With the B77 you may need an inspection mirror. Slowing in rewind and then in play are classic signs of SSS. Back coated tapes tend to be the worst. Tim

24th May 2011, 1:22 am	#6
paolo Heptode Join Date: Nov 2004 Location: Perth, Western Australia Posts: 615	Re: revox B77 problems I agree with Michael. This sounds like Sticky Shed. Your "new old tape" is most likely shedding oxide and gumming up the tape path due to the tape binder chemicals breaking down. Before looking for more alarming problems, I recommend you thoroughly clean the tape guide path with isopropyl alcohol and try again with a different tape. Paul

24th May 2011, 9:34 am	#7
electroanorak Hexode Join Date: Apr 2007 Location: Tonyrefail, Rhondda, South Wales, UK. Posts: 337	Re: revox B77 problems Hi. I have had this problem as well. It was the motor run capacitor. These are known to fail as the get older. Daniel.

24th May 2011, 1:31 pm	#8
djwells01 Triode Join Date: Jun 2010 Location: Norwich, Norfolk, UK. Posts: 22	Re: revox B77 problems Hi David, Could you post the make of tape as this could show a leaning towards SSS or that you do have a fault. Cheers Duncan