Revox A700 - UK Vintage Radio Repair and Restoration Discussion Forum

Vintage-er · 2nd Mar 2020, 8:00 am

My Revox A700 was working OK and I had been just checking some different tapes for about 15 minutes. I left the room with it just turned on but nothing on it - (no spools).

When I returned 5 mins later there was a burning smell & the left side spooling motor was running. Naturally I immediately turned it off.

Before all this, it had not been turned on for about a year.

Any suggestions ?

Thanks.

TIMTAPE · 2nd Mar 2020, 10:50 am

It's probably the Rifa capacitor on the small circuit board near that reel motor has failed. There are a number of them in the machine and all probably need replacing. Not a huge job and parts freely available.

Cheers Tim

DMcMahon · 2nd Mar 2020, 12:13 pm

That is the 0.47uF capacitor on the 3 motor boards, they are also on the Relay board and maybe other places. Also check out the 4.7 ohm resistors on these boards if the capacitor has failed.

David

DMcMahon · 2nd Mar 2020, 1:00 pm

I think the 4.7 ohm only applies to the Spooling motor board and the Relay board.

Ted Kendall · 2nd Mar 2020, 1:05 pm

Yes, change all the Rifas before you do anything else. You may well have got away without further damage - apart from the smell...

Vintage-er · 3rd Mar 2020, 2:09 am

Thanks very much for your replies.

I think I'll need some weight training to tackle this (beautiful) thing !

I have lots of Polystyrene .47uf /250 volt caps in stock. Would these be suitable or should I use higher ratings ?

All this started just because my wife wanted some particular music which is on a very old half track stereo tape I bought new over 50 years ago !

It sounded very good back then so it will be interesting to hear it again if I can get the this Revox to work. The recording is of the "Boys Choir of Vienna" - (Not the Vienna Boys Choir !)

Thanks again.

Michael Maurice · 3rd Mar 2020, 8:53 am

You have to use capacitors rated at AC volts, a standard polystyrene will not be suitable.

I get my from RS using these or these but the stock numbers may not be the same in other countries.

Change ALL the Rifa capacitors, there are about nine on the relay board and one on each of the motor drive boards.

Check all the fuses to see if any have blown and then you can power up. With a little bit of luck all will be ok, if not you'll have to consider replacing some very expensive chips.

Vintage-er · 3rd Mar 2020, 12:22 pm

Thanks Michael. - Is the value of those caps critical ?

I also have a lot of .68uf 600v polyester caps in stock.

Michael Maurice · 3rd Mar 2020, 5:55 pm

I dont think its critical but it must me rated for AC. 600V DC is no good.

Vintage-er · 3rd Mar 2020, 10:38 pm

Thanks Maurice. I'll get the correct ones.

2nd Mar 2020, 8:00 am	#1
Vintage-er Triode Join Date: Jan 2017 Location: Sydney, New South Wales, Australia. Posts: 19	Revox A700 My Revox A700 was working OK and I had been just checking some different tapes for about 15 minutes. I left the room with it just turned on but nothing on it - (no spools). When I returned 5 mins later there was a burning smell & the left side spooling motor was running. Naturally I immediately turned it off. Before all this, it had not been turned on for about a year. Any suggestions ? Thanks.

2nd Mar 2020, 10:50 am	#2
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Revox A700 It's probably the Rifa capacitor on the small circuit board near that reel motor has failed. There are a number of them in the machine and all probably need replacing. Not a huge job and parts freely available. Cheers Tim

2nd Mar 2020, 12:13 pm	#3
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,603	Re: Revox A700 That is the 0.47uF capacitor on the 3 motor boards, they are also on the Relay board and maybe other places. Also check out the 4.7 ohm resistors on these boards if the capacitor has failed. David

2nd Mar 2020, 1:00 pm	#4
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,603	Re: Revox A700 I think the 4.7 ohm only applies to the Spooling motor board and the Relay board.

2nd Mar 2020, 1:05 pm	#5
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Revox A700 Yes, change all the Rifas before you do anything else. You may well have got away without further damage - apart from the smell...

3rd Mar 2020, 2:09 am	#6
Vintage-er Triode Join Date: Jan 2017 Location: Sydney, New South Wales, Australia. Posts: 19	Re: Revox A700 Thanks very much for your replies. I think I'll need some weight training to tackle this (beautiful) thing ! I have lots of Polystyrene .47uf /250 volt caps in stock. Would these be suitable or should I use higher ratings ? All this started just because my wife wanted some particular music which is on a very old half track stereo tape I bought new over 50 years ago ! It sounded very good back then so it will be interesting to hear it again if I can get the this Revox to work. The recording is of the "Boys Choir of Vienna" - (Not the Vienna Boys Choir !) Thanks again.

3rd Mar 2020, 8:53 am	#7
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Re: Revox A700 You have to use capacitors rated at AC volts, a standard polystyrene will not be suitable. I get my from RS using these or these but the stock numbers may not be the same in other countries. Change ALL the Rifa capacitors, there are about nine on the relay board and one on each of the motor drive boards. Check all the fuses to see if any have blown and then you can power up. With a little bit of luck all will be ok, if not you'll have to consider replacing some very expensive chips. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

3rd Mar 2020, 12:22 pm	#8
Vintage-er Triode Join Date: Jan 2017 Location: Sydney, New South Wales, Australia. Posts: 19	Re: Revox A700 Thanks Michael. - Is the value of those caps critical ? I also have a lot of .68uf 600v polyester caps in stock.

3rd Mar 2020, 5:55 pm	#9
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Re: Revox A700 I dont think its critical but it must me rated for AC. 600V DC is no good. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

3rd Mar 2020, 10:38 pm	#10
Vintage-er Triode Join Date: Jan 2017 Location: Sydney, New South Wales, Australia. Posts: 19	Re: Revox A700 Thanks Maurice. I'll get the correct ones.