Revox B77 mk2 not used for a year then switched on but no sound - UK Vintage Radio Repair and Restoration Discussion Forum

QUADGOD · 29th Sep 2020, 6:51 pm

I may be panicking for nothing as I'm very new to R2R so I may have forgotten to move a switch. Last time I used it I recorded something then it was left alone till now. I turned it on and pressed play everything appeared normal apart from no meter movement or sound. Tried a few tapes in case it was blank but nothing.
I'm hoping I've forgotten to change a switch position but I doubt it.
Any thoughts or does it look like a service? Thanks

jamesperrett · 29th Sep 2020, 9:04 pm

The obvious question is what position is the source/tape switch in? Does a signal pass through the machine with the switch set to source?

QUADGOD · 29th Sep 2020, 10:44 pm

It was on tape but I had tried all the controls just in case. Not tried to see if a signal passes through so will try that soon. I gave up and plugged in my back up MK1 with the same tape and that played immediately.
As nothing had been touched on the MK2 since last using it I'm hoping a dirty connection or something minors gone on a pcb. Wishful thinking I know. There wasn't a nasty pop or burning smell noticed after turning it on and everything from drive motors, braking and ff/rewind functioning perfectly.

TIMTAPE · 30th Sep 2020, 2:59 am

Have you checked the heads are clean? For the B77 you need a small inspection mirror.

Michael Maurice · 30th Sep 2020, 10:23 am

Unless the heads are totally and absolutely caked in oxide you would get something if even if was very low and muffled.

TIMTAPE · 30th Sep 2020, 10:30 am

Quote:

Originally Posted by Michael Maurice

Unless the heads are totally and absolutely caked in oxide you would get something if even if was very low and muffled.

Perhaps the repro head is absolutely caked in oxide. Add to that a playback speaker with poor bass response and the result could well be the sounds of silence.

But I would listen at high gain for the repro preamp noise and some induced mains hum, which should increase when the hum flap is manually (temporarily) swung away.

QUADGOD · 30th Sep 2020, 10:32 am

Heads fine

TIMTAPE · 30th Sep 2020, 10:42 am

Quote:

Originally Posted by QUADGOD

Heads fine

Great. Next step, can you hear the playback preamp noise (hiss and a little hum)? It only switches on in "play" mode. Is it the same both left and right channels?

Is it possible the tape side was flipped? (180 degree twist).

Is it possible the tape was accidentally threaded behind the hum flap rather than in front of it? Sounds silly but I've seen machines with the tell tape oxide deposits on the back side of the flap.

Just eliminating the easily checkable before deeper diving.

rontech · 30th Sep 2020, 1:42 pm

In the late 1980's my 10 yr old B77 suffered intermittent operation of the various switches.

QUADGOD · 2nd Oct 2020, 3:45 pm

I may as well clean switches and run through obvious cleaning everywhere but considering it was working 100% about a year ago I'm guessing something died when it fired up this week

Michael Maurice · 2nd Oct 2020, 10:43 pm

Assuming the capstan motor is running, you can rule out the power supply.

We need to know if an input signal will pass through the machine with the monitor switch set to source.

If it does, the fault is in the reproduce amplifier board, if not, the fault may be in the monitor board.

If the fault is on the reproduce board, check C21 which decouples the supply to the preamp stages of this board. It may be short circuit.

QUADGOD · 12th Oct 2020, 8:28 pm

Sorry I've been away on long holiday. OK thanks I will check that and depending on what happens take the correct board to an engineer to fault find for me. Thank you

Michael Maurice · 12th Oct 2020, 8:37 pm

If you get into difficulties, let me know, I'll be coming up to Bedford some time soon.

QUADGOD · 13th Oct 2020, 8:18 pm

OK cheers good to know...

29th Sep 2020, 6:51 pm	#1
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Revox B77 mk2 not used for a year then switched on but no sound I may be panicking for nothing as I'm very new to R2R so I may have forgotten to move a switch. Last time I used it I recorded something then it was left alone till now. I turned it on and pressed play everything appeared normal apart from no meter movement or sound. Tried a few tapes in case it was blank but nothing. I'm hoping I've forgotten to change a switch position but I doubt it. Any thoughts or does it look like a service? Thanks

29th Sep 2020, 9:04 pm	#2
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,873	Re: Revox B77 mk2 not used for a year then switched on but no sound The obvious question is what position is the source/tape switch in? Does a signal pass through the machine with the switch set to source?

29th Sep 2020, 10:44 pm	#3
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B77 mk2 not used for a year then switched on but no sound It was on tape but I had tried all the controls just in case. Not tried to see if a signal passes through so will try that soon. I gave up and plugged in my back up MK1 with the same tape and that played immediately. As nothing had been touched on the MK2 since last using it I'm hoping a dirty connection or something minors gone on a pcb. Wishful thinking I know. There wasn't a nasty pop or burning smell noticed after turning it on and everything from drive motors, braking and ff/rewind functioning perfectly.

30th Sep 2020, 2:59 am	#4
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Revox B77 mk2 not used for a year then switched on but no sound Have you checked the heads are clean? For the B77 you need a small inspection mirror.

30th Sep 2020, 10:23 am	#5
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,222	Re: Revox B77 mk2 not used for a year then switched on but no sound Unless the heads are totally and absolutely caked in oxide you would get something if even if was very low and muffled. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

30th Sep 2020, 10:32 am	#7
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B77 mk2 not used for a year then switched on but no sound Heads fine

30th Sep 2020, 1:42 pm	#9
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: Revox B77 mk2 not used for a year then switched on but no sound In the late 1980's my 10 yr old B77 suffered intermittent operation of the various switches. __________________ Time flies like an arrow, fruit flies like a banana

2nd Oct 2020, 3:45 pm	#10
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B77 mk2 not used for a year then switched on but no sound I may as well clean switches and run through obvious cleaning everywhere but considering it was working 100% about a year ago I'm guessing something died when it fired up this week

2nd Oct 2020, 10:43 pm	#11
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,222	Re: Revox B77 mk2 not used for a year then switched on but no sound Assuming the capstan motor is running, you can rule out the power supply. We need to know if an input signal will pass through the machine with the monitor switch set to source. If it does, the fault is in the reproduce amplifier board, if not, the fault may be in the monitor board. If the fault is on the reproduce board, check C21 which decouples the supply to the preamp stages of this board. It may be short circuit. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

12th Oct 2020, 8:28 pm	#12
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B77 mk2 not used for a year then switched on but no sound Sorry I've been away on long holiday. OK thanks I will check that and depending on what happens take the correct board to an engineer to fault find for me. Thank you

12th Oct 2020, 8:37 pm	#13
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,222	Re: Revox B77 mk2 not used for a year then switched on but no sound If you get into difficulties, let me know, I'll be coming up to Bedford some time soon. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

13th Oct 2020, 8:18 pm	#14
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B77 mk2 not used for a year then switched on but no sound OK cheers good to know...