ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
greetings all,
i posted that problem previously
in the meantime I replaced the SIEMENS muting relay on the main board with a new one and the output
signal still goes silent from time to time ?? comes back after a while, drops out again and sometimes play for half a day without a problem !!
finding the 'nasty' seems difficult as I can not detect a pattern here.
could it be a problem with the RIAA pre-amp ? just guessing here.
or is a voltage breakdown at the muting relay likely ??
when the signal drops out it goes out instantly without a crickle or crackle or any distortion-foreplay and comes back just as quickly.
don't just want to change parts blindly on the off-chance to have got the sick one.
anybody out there who might have a better idea or suggestion ??
I am simply stuck with that problem........
cheers ALF
If we agree that the main board is the one under the platter, fitted solder side up, it doesn't handle the muting at all.The relay on that board is for speed switching 33/45.
If no decoder is fitted in your deck, (that's a heavily populated board sitting under the operation panel, component side up) therewill be a muting relay on the board fitted instead and only about a handful of other components.This relay will merely ground the output signals, it won't break the signal path. This means that in case of intermittent contactsthe sound will (intermittently) NOT be muted, resulting in audible thump sounds when the cartridge lands on the record.
Martin
Hello martin,
Thank you for responding - we can agree the main board solder side up is under the platter - has a fairly large Siemens relay fitted - now a brand new one !
The board under the control panel - board 6 - is heavily populated, so this one must be the decoder - I plug the table straight into a line-level input.
The board under the 4002 control panel only has a few components in contrast.
Anyhow, does that mean the muting circuit sits on the decoder-board but has nothing to do with th signal drop-outs ??
It Is tricky to describd the sound it makes when the signal drops in or out.......probably sounds more like the stylus makes a mild 'crash-landing'
on the record ?!
Am I still barking at the wrong tree here or is the problem decoder-output related ??
ALF
The main board does not handle anything sound-related. That's all done on the decoder board.If the problem affects both channels simultanously, the problem must be in a common circuit.Intermittent faults can be tricky to cure but check the power supply for correct voltages and amount of ripple.If all good - put a scope to the signal path and see where the signal is lost.Local cooling/heating could also help narrow down the problem area.
hello martin,
yes, of course the 1RL1 handles the speeds......just looking at the circuit diagram says it all !
must say, I had been misguided by someone pointing out to me the RL1 Siemens relay as the muting relay :-(
perhaps a simple misunderstanding ?!
well, quite right: intermittent faults are just what one needs !
both channels are simultaneously affected by the signal drop outs/ins.
that could not be caused by a single transistor or capacitor as I understand it ?!
I shall have another look at the Board 6 diagram, although I have to admit I am getting into DEEEEEP waters here ........
where staying afloat is the issue
hi martin,
I took 2 shots from the decoder board in my table to better illustrate my concerns....
also find it hard to match with the service manuals available as most of these boards seem to look different ?!
that big fat blue 1000uF cap looks suspicious with corrosion on its lead wires !
cheers, ALF
quite right what martin pointed out - thanks !!! - intermittent faults are difficult to trace but in this case
the pointer towards the 'common circuit' was spot on.
I am cautiously optimistic that the culprit has been found - I replaced TR102 and no further
signal drop-outs since then :-)) shall we call it 'CASE CLOSED' ?!!
thank you to all who tried to help