Hi Mark,

thank you kindly for your reply.

S3 gets activated by the lower camwheel and IC1 sends the up or down signal via TR5 to RL2 which in return

activates the lower control arm that is connected to the lower camwheel responsible for blocking that camwheel once the PU arm is lowered. For that to happen the solenoid must generate enough energy to move that control arm via its piston.

as I understand if that control arm is not moved far enough the lower camwheel keeps turning and activating S3

over and over again.

I am happy to be corrected if my theory is wrong.

I accept that TR4 and TR5 don’t have to be matched, which was just an assumption. But what is actually energising the solenoid I like to understand and is TR6 alone responsible for the motor control or does it play a role towards the solenoid as well ??

yes, I can measure the muting switch which does open and close when operating arm N (SM drawing).

i will report back

ALF

I measured the resistance of the muting switch as per SM:

0.1 Ohm with the PU arm raised - switch in pressed position

10.5 Ohm with the PU arm lowered - switch in depressed position

does that make sense ? I could not find any reference values of the switch’ resistance readings.

BTW, which one is TR% ??

ALF

Apologies, a typo:

the muting switch resistance, measured in playing mode was 0.1 Ohm and 14.5 Ohm, not 10.5 Ohm !!

hope that still makes sense.

My guess is the mentioned TR% should read TR6 ?!

ALF

I don’t believe you are measuring the correct contacts with those results. The muting switch is different depending on whether you have the version with the built-in RIAA preamp. In either case, when the tonearm is up, you should get 0 ohms or .1. This is a two pole switch meaning there are two sets of contacts. With it down, you should get 800-1K ohms w/o the module and around 5K-7.3K ohms with it depending on the input impedance of your amp..

All Beogram 6500 models are fitted with the RIAA module.

I measured as per SM 5-4 Muting, assuming the drawing shows the solder side of the muting switch PCB.

if your readings are the correct ones then my muting switch does not work which coincides with the fact

that there is no audio output at the moment no matter which cartridge is fitted !

in that case I shall try to bypass the switch…..

ALF

What I meant was

i have never seen a BG6500 w/o the RIAA board, perhaps there are early versions w/o that board ?

i revisited the SM 2-2 , studied the drawing of the new version RIAA board and measured between

the RM and LM contacts of the switch but still, I can not verify your data.

this particular drawing there also  mentioned cuts (RM, LM and LG) - I  presume this is for bypassing the muting switch ?

after I removed those 3 wires I fitted a different cartridge to check the audio output….nothing again ??

strangely enough the BG plays again (at the moment).

Both cartridges appear to be in perfect health and were working before ??? So, I really don't know where

all this is heading ? PU arm wiring ? RIAA board fault ?

If indeed I bypassed the muting switch by removing those 3 wires I may have a faulty RIAA board ??

any further thoughts ?

ALF

I would first check the cartridge coils which can be done by measuring between the R & GR and the L & LG pins. Depending on which cartridge you have they should measure between 800-1K ohms for each channel. I would then check that the RIAA board is getting 12v  especially the collector of TR2 which is a quad bilateral switch IC that also acts as a mute. If the 12v is not on available from TR2 to pins 5, 6, 12, & 13, then you will not get sound even with a good cartridge. You should also have 12 on pin 8 of IC2 and IC3.

First of all a big Thank You for your support - very much appreciated 👍

second, I did not check any cartridge coils as I was dead sure the MMC2 and MMC4 were working

perfectly before…..and still are.

Now everything is back to normal (for now but one can never be sure 😁) - shat happened ?

the RIAA board did not get any voltage because P2 at the power supply board wasn’t properly plugged in.

this must have happened when I had to replace the fuse which is right next to it. While levering out the fuse

it partly unplugged P2. the RIAA board is back in business and so is the audio signal 🙏🏼

i was certain the 12V supply was working but did not expect this small hick-up……and the muting switch

works fine as well !

why the previous issues have suddenly disappeared is not quite clear to me - one fact was that the wrong

fuse had been installed - a slow blow 500 mA fuse instead of 750mA.

anyway, i was certain all camwheels were installed correctly and the piston in the solenoid is not deformed

and moves freely…..

I rest my case for now, once again thank you for being so patient and helpful

ALF