Revox A77 Playback Problem - UK Vintage Radio Repair and Restoration Discussion Forum

cgehansen · 9th Jul 2020, 12:59 pm

Hi, I have a Revox A77 which I'm trying to get working again. It's got an issue with one of the Repr Amps. It was completely dead with no playback at all. I've changed the tantalum capacitors as two of them had shorted and also the electrolytics. There is now playback when I select 'input' but not from the tape. If I swap the card for a good one I get playback from input and the tape. I don't have a scope so can't test it properly. Is there a part or parts that could cause this issue? Thanks Christian

Michael Maurice · 9th Jul 2020, 11:49 pm

Transistors have been known to fail, i suppose resistors could go high, A more likely cause is the preset pot for the reproduce level. The slider breaks off so you get no output. Its a simple thing to replace.

TIMTAPE · 10th Jul 2020, 6:13 am

To add, as always check the polarity orientation of the capacitors you have replaced.

cgehansen · 10th Jul 2020, 7:30 pm

Thanks. It was the preset pot. It looked fine but wasn’t making contact. Now it’s fallen apart completely.

9th Jul 2020, 12:59 pm	#1
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Revox A77 Playback Problem Hi, I have a Revox A77 which I'm trying to get working again. It's got an issue with one of the Repr Amps. It was completely dead with no playback at all. I've changed the tantalum capacitors as two of them had shorted and also the electrolytics. There is now playback when I select 'input' but not from the tape. If I swap the card for a good one I get playback from input and the tape. I don't have a scope so can't test it properly. Is there a part or parts that could cause this issue? Thanks Christian

9th Jul 2020, 11:49 pm	#2
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,222	Re: Revox A77 Playback Problem Transistors have been known to fail, i suppose resistors could go high, A more likely cause is the preset pot for the reproduce level. The slider breaks off so you get no output. Its a simple thing to replace. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

10th Jul 2020, 6:13 am	#3
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Revox A77 Playback Problem To add, as always check the polarity orientation of the capacitors you have replaced.

10th Jul 2020, 7:30 pm	#4
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Revox A77 Playback Problem Thanks. It was the preset pot. It looked fine but wasn’t making contact. Now it’s fallen apart completely.