Sony amp (F411R). Loss of sound at low volumes on power on - UK Vintage Radio Repair and Restoration Discussion Forum

jmcilkley · 24th Sep 2020, 8:31 am

Can anyone point me in the right direction here? I have quite an old Sony amp (F411R) and often (but not alway) when I power it on I get sound from only the left channel and occasionally no sound at all from either. Turning up the volume instantaneously restores the sound and then turning it back down again it continues fine.
I've done all the obvious things, de-ox'ed the volume pot (and all the other ones), checked solder connections on the output, etc. But it still does it and I don't know where to look next.
Once it starts working it is perfect. If I don't touch the volume control then the sound doesn't come back on the faulty channel - so it's not just a warming-up problem.
Any ideas?

Andrew2 · 24th Sep 2020, 9:02 am

Faults like you describe are frequently due to oxidised switch contacts or poor connections to speakers or ancilliary gear. Turning up the wick is often enough to break through the oxide and resore normal operation until next time.
Selector switches, pots, phono connections, speaker fuses/relays and speaker terminals are all under suspicion.

ajgriff · 24th Sep 2020, 9:52 am

I agree that poor contacts somewhere are likely to be the cause. The protection relay would be a prime suspect although it's not usually very easy to clean the contacts and replacement is often the best option for long term reliability. The manual doesn't say anything about the relay's spec but markings on the relay itself might help. By the way, the service manual can be downloaded for free from Hi-Fi Engine if you don't already have a copy. An amp that's worthy of some TLC in my view.

Alan

Goldie99 · 24th Sep 2020, 11:56 am

Another possibility with Sony's of that age would be any rotary remote slide switches it might have - the contacts are in the slide portion of the switches, and they are inaccessible for cleaning without removal from the pcb. I've had issues on slides for source selection or speaker selection, in different Sony's.

Alan

jmcilkley · 25th Sep 2020, 6:16 pm

Thanks for those suggestions. I have cleaned all the rotary switches but haven't check the protection relays. When I power on I can hear the relays click so I had assumed they were ok but maybe worth a look.

ajgriff · 25th Sep 2020, 6:42 pm

There's only one relay. The clicking's good but there could still be a problem with the contacts for the intermittent right channel. Have a look at the schematic.

Alan

24th Sep 2020, 8:31 am	#1
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Sony amp (F411R). Loss of sound at low volumes on power on Can anyone point me in the right direction here? I have quite an old Sony amp (F411R) and often (but not alway) when I power it on I get sound from only the left channel and occasionally no sound at all from either. Turning up the volume instantaneously restores the sound and then turning it back down again it continues fine. I've done all the obvious things, de-ox'ed the volume pot (and all the other ones), checked solder connections on the output, etc. But it still does it and I don't know where to look next. Once it starts working it is perfect. If I don't touch the volume control then the sound doesn't come back on the faulty channel - so it's not just a warming-up problem. Any ideas?

24th Sep 2020, 9:02 am	#2
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,038	Re: Loss of sound at low volumes on power on Faults like you describe are frequently due to oxidised switch contacts or poor connections to speakers or ancilliary gear. Turning up the wick is often enough to break through the oxide and resore normal operation until next time. Selector switches, pots, phono connections, speaker fuses/relays and speaker terminals are all under suspicion. __________________ Andy G1HBE.

24th Sep 2020, 9:52 am	#3
ajgriff Nonode Join Date: May 2004 Location: Halifax, West Yorkshire, UK. Posts: 2,587	Re: Sony amp (F411R). Loss of sound at low volumes on power on I agree that poor contacts somewhere are likely to be the cause. The protection relay would be a prime suspect although it's not usually very easy to clean the contacts and replacement is often the best option for long term reliability. The manual doesn't say anything about the relay's spec but markings on the relay itself might help. By the way, the service manual can be downloaded for free from Hi-Fi Engine if you don't already have a copy. An amp that's worthy of some TLC in my view. Alan

24th Sep 2020, 11:56 am	#4
Goldie99 Heptode Join Date: Jul 2014 Location: Boston, Lincolnshire, UK. Posts: 995	Re: Sony amp (F411R). Loss of sound at low volumes on power on Another possibility with Sony's of that age would be any rotary remote slide switches it might have - the contacts are in the slide portion of the switches, and they are inaccessible for cleaning without removal from the pcb. I've had issues on slides for source selection or speaker selection, in different Sony's. Alan

25th Sep 2020, 6:16 pm	#5
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Re: Sony amp (F411R). Loss of sound at low volumes on power on Thanks for those suggestions. I have cleaned all the rotary switches but haven't check the protection relays. When I power on I can hear the relays click so I had assumed they were ok but maybe worth a look.

25th Sep 2020, 6:42 pm	#6
ajgriff Nonode Join Date: May 2004 Location: Halifax, West Yorkshire, UK. Posts: 2,587	Re: Sony amp (F411R). Loss of sound at low volumes on power on There's only one relay. The clicking's good but there could still be a problem with the contacts for the intermittent right channel. Have a look at the schematic. Alan