Revox B790 Service problems

[BoringSounds]

Dear All,
I have just completed a service of a Revox B790
problems before the service:
relay not working, so when the needle dropped you would hear it.

I thought to service the caps and see if that made a difference.

I bought a service kit from http://www.revox-online-shop.de
to replace all the caps. I also purchased a replacement relay (which is still not fitted).

Everything was going well after the service, apart from the fact that the relay was still not working. It played well, for about 4Lps and then one channel died and then finally the other.

So then I replaced the Q3 transistor 2N 4403 (with the listed equivalent BC 237) which apparently controls the relay. After replacing this, the sound was working out of both channels with the relay now working, but the light system for the tonearm was no longer functioning, nor the end stop.

I thought that maybe I had put the Q3 transistor around the wrong way (although I had checked the pin out before). I double checked and it was correct. So I purchased some other variants of BC 237, I replaced it and then I had the light working again for the tonearm and the end stop function working. But no sound coming out at all!!! I turned around the transistor just so see if maybe the manual was incorrect (happens sometimes) and I got sound out but no light!!!

So I returned it back to the correct way and tried to make the relay to be closed and I got sound out albeit a very low somewhat distorted signal through the phonostage..

I left this on the workbench for some days, as I did not want to take a hammer to the thing...

Current state of the machine things not working:
No sound coming out!
Things working:
Everything else...

So now I am trying to figure out what has happened to the thing.

Why would having the pin outs on Q3 back to front allow sound to pass through but no lights..

Now the thing I am worried about is that if I replace the relay with the new one what if I make matters worse?

relay link

Thank you in advance for your patience in reading my lengthy post and any ideas are very welcome...
atb
David

 

[Vinylcafe]

AK Member boyerd001 is an expert on these turntables.
You might try to send him a PM.
I have a 791 and he's helped me in the past.
Good luck with it.
Be persistent and you will get it done.
Why not install the relay; it might be the cause of your problem.
I am no expert, and maybe others can chime in here, but I do not think you can harm the relay, unless perhaps voltages or current exceed spec, or maybe polarity is reversed, which I presume you would not do.

 

[Pio1980]

NONE of the circuitry other than the relay and passive signal paths are part of the signal path to include ALL capacitors and active devices like ICs and transistors.
If the relay is working,

IIRC, the relay is a "crowbar" muting device that shorts signal lines to signal common/gound and cannot affect audio unless the contact are fouled or actually sticking.
Look for problems with the cart, the pigtails between the cart carrier and tracking board on the carrier trolley, relay contacts & relay board solder pads, and the signal lines to preamp. I think you could have a possible problem with fouled and broken pigtails, check there first as it is easiest. Next, recheck your ckt board work for solder bridges around relay and signal path, and everywhere else with good light and strong magnification. Been there & done that too many times with old eyes and clumsy hands here.
Forgive me if I appear to be impugning the quality of work but it's usually helpful to backtrack when new problems appear afterward. I don't envy anyone who has to work on these boards BTW.

 

[BoringSounds]

IIRC, the relay is a "crowbar" muting device that shorts signal lines to signal common/gound and cannot affect audio unless the contact are fouled or actually sticking.
Look for problems with the cart, the pigtails between the cart carrier and tracking board on the carrier trolley, relay contacts & relay board solder pads, and the signal lines to preamp. I think you could have a possible problem with fouled and broken pigtails, check there first as it is easiest. Next, recheck your ckt board work for solder bridges around relay and signal path, and everywhere else with good light and strong magnification. Been there & done that too many times with old eyes and clumsy hands here.
Forgive me if I appear to be impugning the quality of work but it's usually helpful to backtrack when new problems appear afterward. I don't envy anyone who has to work on these boards BTW.

Hi, thanks to both of you for your input. It does seem that it is a problem with the relay, because when the transistor is around the wrong way there was sound just no lighting and endstop control. So I think I will try to replace the relay and move on from there.

No offense taken by your careful suggestion of retracing my steps and double checking my soldering. I have done this a couple of times, with a magnifying glass checking for shorts and dry solder joints. I also agree these boards are a royal pain in the a... to work with.

atb
David