Help for an old n00b - buzzing from Technics deck

[JoMo]

Hi,

I recently rescued a Technics SL-B202 from a neighbour's skip (got the OK from him to do so!). Initially it wasn't powering up but after a session with a screwdriver, a soldering iron and a multimeter, it lives!

A couple of issues though.

1. There is no ground wire. Initially it occurred to me that perhaps it was grounded through the mains earth, but it buzzes so perhaps not. There doesn't appear to be a broken wire/terminal or anything inside that I could see. So can anyone advise as to whether it needs a ground and if so how I should wire one in? What does this ground need to be connected to inside the turntable?

2. Initially at least, the speed can vary slightly causing a wobbly pitch. This tends to settle down after a short while but ideally I'd like to fix it. Is there anything anyone can tell me as to how this might be achieved? Hopefully it's not a failure of the hall effect IC that sits under the motor - can't imagine that's easy to get a replacement for these days?

I have paired the turntable with a Kenwood 5020 integrated amp and some Celestion F10 speakers.

Thanks. JoMo

 

[abacus]

If the picture is how you use it, then it may be picking up radiation from the transformer in the amp, so try moving them apart.

Bill

 

[JoMo]

If the picture is how you use it, then it may be picking up radiation from the transformer in the amp, so try moving them apart.

Bill

Tried them side by side - no difference 😞

 

[Gray]

Tried them side by side

As far apart as the cable will allow?
With the right hand (arm side) of the deck furthest from the amp?

With the grounding issue:
Have a look at where the signal leads are going inside....as well as the cable screens being returns for the cartridge channels, is one of them paired off to metal chassis?
(That's how Rega do it and why they don't have a separate earth lead).

Show us a good picture of the internals if you like.

 

[JoMo]

As far apart as the cable will allow?
With the right hand (arm side) of the deck furthest from the amp?

With the grounding issue:
Have a look at where the signal leads are going inside....as well as the cable screens being returns for the cartridge channels, is one of them paired off to metal chassis?
(That's how Rega do it and why they don't have a separate earth lead).

Show us a good picture of the internals if you like.

I really don't think it's a case of proximity. I have tried carrying the turntable as far away as possible from amp and speakers while connected - no difference.

Looking at the wiring, I'm pretty convinced that the ground is routed through the mains cable.

You can see the mains cable coming in on the right (to the brown circuit board with the fuse on it) and the phono cable coming in the centre to the green circuit board. The earth wire (green & yellow) runs from the mains cable and terminates on a pad on the grren board that is in turn connected to the fine black wire that runs up the tonearm. A continuity test shows that this pathway between mains plug and the circuit board pictured is intact.
The continuity between earth terminal on mains plug and the top of the tonearm is also intact. I suppose the cartridge could be faulty, I would have to find another one to try...

Would the fact that earth is provided via mains and not grounded to the amp make a difference? I don't know, I could try running a wire from the earth to the amp ground. Again, not sure if that would make any difference. Wouldn't think so but that's why I'm here!

Note that in the picture I've unscrewed the shielding over the green circuit board to show you what lies beneath.

 

[Gray]

Looking at the wiring, I'm pretty convinced that the ground is routed through the mains cable.

You're right, it is - and your continuity tests have proved it 👍
If your amp uses a 3-core mains cable - check continuity between the earth pin of its plug and the outside (screen) of the RCA phono input sockets.
If there is continuity, then that earthed pad in the turntable already has a connection to your amp's earth.....but if your amp has a 2-core mains cable, you could try soldering a link between the earth pad and the screen next to it (which would effectively be doing the same as running a wire from pad to amp socket ground of course).

It's likely that someone other than Technics has run that mains earth cable to the pad - certainly the case if there's no bolt through to chassis at that point - because there's no way an electrical safety earth would be allowed to rely on that little thin black wire.
(OK as an audio ground wire but not for handling the necessary current in the event of the chassis becoming live - in a house with no earth leakage circuit breaker).

I'd be checking that next if I were you.
Isolate the thin black wire from the pad - and see if the earth wire still has its own direct continuity to the chassis......

 

[JoMo]

Excellent news - like Bon Jovi, we're half way there! I ran a wire (ok, a bit of solder because I couldn't find any wire ) from the internal shield of the turntable (which is electrically connected to the earth terminal via a screw) to the ground peg of the amplifier and... hum begone! 🧙‍♂️

So I just have to finalise that connection somehow and we should be hot to trot. So thank you for your input @Gray . Like you alluded to, I think the amp power cable is a two wire job (no earth) so obviously wasn't happy with the turntable going to a ground that it didn't know about.

If anyone has any clue about the varying speed please let me know! My first port of call will be to give a few components a good squirt of contact cleaner.

JoMo

 

[nopiano]

If anyone has any clue about the varying speed please let me know! My first port of call will be to give a few components a good squirt of contact cleaner.

It’s a belt drive, isn’t it? Maybe the spindle bearing is dry, the belt perished, the motor pulley dirty? Lots to check! Careful with spray near belts too.

Re the Earth, there wasn’t a mains one according to the manual, but there was for the arm.

Technics SL-B202 user manual (8 pages)

Manual Technics SL-B202. View the Technics SL-B202 manual for free or ask your question to other Technics SL-B202 owners.

www.manuals.co.uk

 

[Links]

I have an SL D 303 this has a ground wite and I guess your B 202 should have one too .With one I have no hum problems.