UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players

Notices

Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

Closed Thread
 
Thread Tools
Old 18th May 2014, 7:41 pm   #1
dockyard
Retired Dormant Member
 
Join Date: May 2014
Location: Gilligham Kent UK
Posts: 3
Angry Revox A77 No rewind

Hello all
First I am a new member who is just getting back into tape after many years with old recorders gathering dust in the loft.
The problem I would like help with concerns both my Revox A77's.
One I bought with a good history and in working order it was refurbished my Brian Reeves a Uk Revox agent about 10 years ago but has not been heavily used since then. The second I bought on ebay for parts not working but I got intesested and decided i would try and get it going.
My problem started when I fitted the relay board from the working recorder to check out the problems with the non working recorder. It made no difference so I put it back only to find I had no rewind the same problem on BOTH recorders. Before I changed the boards both rewinds were working!
So far I have switch relays around, replaced the rifa caps, replaced the motor power caps, switched reel motors, put a meter on the resistors and diodes (although I read somewhere the diodes dont affect the rewind). I should say both are Mk3's and I do have a service manual but limited electronic knowledge.
Any ideas would be appreciated.
dockyard is offline  
Old 19th May 2014, 3:36 pm   #2
SteveCG
Nonode
 
Join Date: Jun 2009
Location: Herefordshire, UK.
Posts: 2,495
Default Re: Revox A77 No rewind

Since you've obviously uncased both the Revoxes, you have plugged the external remote control links back before trying the machines have you?

I once spent some time puzzing over non-operation until the penny dropped !
SteveCG is offline  
Old 19th May 2014, 6:40 pm   #3
dockyard
Retired Dormant Member
 
Join Date: May 2014
Location: Gilligham Kent UK
Posts: 3
Default Re: Revox A77 No rewind

Yes the plug has been replaced, I am looking what could be common to both machines Is the relay board the only thing that would cause the problem?
dockyard is offline  
Old 19th May 2014, 10:21 pm   #4
ben
Dekatron
 
ben's Avatar
 
Join Date: Aug 2006
Location: Madrid, Spain / Wirral, UK
Posts: 7,484
Default Re: Revox A77 No rewind

Have you got a multimeter? a cheap one from maplin or market stall will do. Without one, you're gong to have a hard time tracking this.

Start with some voltage measurements at the motor and work back from there, via relays, switch contacts, pcb fuses etc. Somewhere you'll find where it goes missing.
__________________
Regards,
Ben.
ben is offline  
Old 20th May 2014, 10:22 am   #5
SteveCG
Nonode
 
Join Date: Jun 2009
Location: Herefordshire, UK.
Posts: 2,495
Default Re: Revox A77 No rewind

Revox used skeleton preset resistors (also known as preset potentiometers) in quite a few places in their machines. These unfortunately have not proved to be long-living. The problem is that the metal that the wiper arm of the preset is made out of has corroded, with the result that the wiper arm may fall off of its own accord, or may fall off if the tape recorder is bumped or if one attempts to adjust the value of the preset.

As Ben says, the first thing to do now, since you have a service manual, is to check with a meter that the supply voltages are what the service manual says they should be. It may be that the preset in the power supply unit has failed on both machines.

I just wish to emphasize that this preset problem is a very common problem - even for machines that have been carefully looked after.
SteveCG is offline  
Old 21st May 2014, 4:32 pm   #6
Polarrestorer
Retired Dormant Member
 
Join Date: May 2014
Location: Daventry, Northamptonshire
Posts: 4
Default Re: Revox A77 No rewind

Beware laying an A77 face down: the pot controls will, if pushed inwards even slightly, demolish the potentiometer (being skeletal, they just can't take it.) Maplin's and others stock similar, but one has to make up an adapter for the shaft.
Polarrestorer is offline  
Old 21st May 2014, 9:57 pm   #7
dockyard
Retired Dormant Member
 
Join Date: May 2014
Location: Gilligham Kent UK
Posts: 3
Default Re: Revox A77 No rewind

Sorted, thanks for your help. I started to check motor voltages and soon realised I had crossed the two green coloured wires which meant the motor was not connected as intended!!! I did the same on both machines hence no rewind.
So now I need to have a closer look at my ebay spares project to see why it wont record. I will report back later as I am sure I will come against another (to me ) brick wall, still it keeps the brain working.
dockyard is offline  
Old 21st May 2014, 11:19 pm   #8
Ian E G7OLT
Pentode
 
Ian E G7OLT's Avatar
 
Join Date: May 2009
Location: Byfield, Northamptonshire UK.
Posts: 112
Default Re: Revox A77 No rewind

Make sure the rewind button is actually closing the switch on the board. I had a problem myself once after I'd had the board out to ensure the edge contacts were clean, only to lose rewind after I replaced it!
Ian E G7OLT is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 12:05 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.