The timmers will be oxidised, and I also replace the speed change relay as these can be responsible for sudden speed fluctuations. You could try spraying some contact cleaner as a quick fix but that is all it will be. Go for reasonable quality parts i.e. Piher trimmers and a known name relay, just be wary of the pin configuration!!! This will catch out the most experienced ;)

@Olly

Sorry for my late response.....Thanks for your prompt response, mate.

I forgot to mention I had some contact spray that I applied already to the trimmers.  Might be why it work for a couple of minutes before it started freaking out....I will try it again.  There was obvious oxidization on the circuit board trimmers, it was a discoloured dark colour (almost black).  

Which trimmers would you suggest changing? Just the 33RPM one on the circuit board? And where would I find the speed change relay?  I have the service manual at home so I will take alook tonight but some advice to where it is would be great.  I have alot of experience soldering so I'm not phased with doing it myself, I would just need to make sure I'm working on the correct components.

Ross

You've already identified the possible causes:

1. Belt - you've done.

2. Replace the 33 speed trimmer on the main circuit PCB - use Piher PTC10 Cermet unit.

3. You may need a new speed-change relay, but that's a complicated setup. I have  standard Schrack replacements, but you need to wire it correctly - the original Siemens unit has non-standard reverse wiring.

4. The round 33 trimmer with the hex-hole under the keyboard - that's what I'd concentrate on immediately as the culprit. Disconnect / Bypass it, and see if the problem disappears. If it works Ok without it, then that's the bad part, and it's a journey to find a replacement. But the system will work just fine without it, as long as your main 33 trimmer (the new Piher unit) on the main PCB is adjusted spot-on.

Menahem

@ Menahem Yachad

Thanks for the advise, its much appreciated.

I'm unsure as to what ohm Piher PTC10 to get? Looking at the service manual it's, 50K ohm Piher Horizontal Trimpot.

The PTC10 is a special type, adjustable from both the top and bottom, which you need on all the BeoGram circuit boards, and in many of the BeoMasters as well.

Consider doing both potis while you're at it.:

45rpm 4.7K  PTC10LV10-502

33rpm 50K  PTC10LV10-503  

Enter these exact part numbers on Mouser's website, and you'll get exactly what you need.

Another idea I just had, if this still doesn't solve your problem, is - if you don't use the 45 speed - to swap the 2 trimmer pots on the keyboard PCB. If the problem transfers to the 45 side, then you've isolated it. Being that those trimmers are unobtainable, you could probably live with the 45 side being non-functional (or as I said before, just bypass that trimmer).

Menahem

Dear Menahem,

many thanks for your extremely helpful and interesting contributions.

Re;   my own BG 4000 Proj.

"3. You may need a new speed-change relay, but that's a complicated setup. I have  standard Schrack replacements, but you need to wire it correctly - the original Siemens unit has non-standard reverse wiring."

could you be so kind and indicate the Mouser Part No. for this relay ?

I fear that this part has also failed in my BG 4000 project.    I have a Mouser Office with an excellent Technical   support nearby.  Some finer details from you about wiring -in the Schrack relay into the BG 4000 Main PCB would be of great help too !!.

thanks in advance & best rgds

Zorb.

(Munich)

Hi Zorb

Here is the original B&O wiring diagram of the Siemens relay.

You need to wire the new Schrack RTE24024F relay the same way.

Of course, it does not fit on the existing BeoGram PCB, so you need to tape it down elsewhere and run the wiring to the PCB.

Menahem

Grateful thanks Menahem, you are very kind.

Allthough space is tight in the BG,  I'll find a corner somewhere.

If I can source anything for you in Bavaria (or German Schweiz),  please mail me.

Wishing you further success

Zorb.