Repairing Siemens W295 EQ

[Tritalos]

Hi,
I racked a pair of Siemens W295 EQs together with a new PSU and a swotching board for bypass, external inserts, changing prepost eq.
I removed the cases of the eqs and only mounted the board, using new rotary switches for everything.

Now the problem is an issue with one of the EQs. While one works perfectly fine, the second one has a weird kind of a loose connection, resulting in a hicut at around 100hz. I cannot find any lose part, or any unhealthy looking connection or part. Sometimes, it just works the whole day, and without touching, hicuts again. Pressing the frontplate sometimes ends the problem, sometimes its pressing the back end of the pcb.
I would highly appreciate any input or a better place to ask, if this should be the wrong one.
Cheers,
Simon

 

[iprovlek]

Here is the schematics!!!

 

[iprovlek]

Maybe you have cold joints on rotary switches that you changed!!!

 

[Tritalos]

Thanks for the schematics. I tried to find an explanation in the circuit but no siccess so far.
I'll check for cold joints again but I already did. It would be the first in years, but never say never, right?
I don't think it's on the switches though, bc it changes when I put some pressure on the other end of the circuit board, which is only connected via wires with the switches.

 

[iprovlek]

Try pull of that 2 PCB boards out which are connected to gold pins, clean and turn it back in place!!!

Maybe some dirt cause this....

 

[iprovlek]

This one behind rotary switches, and one before output and input trannie.....

 

[Whoops]

Thanks for the schematics. I tried to find an explanation in the circuit but no siccess so far.

Tap with a chopstick in each component one by one, each wire connection, each solder joint, each contact, while listening to the circuit

 

[Tritalos]

Thank you for your help.
I tried both, cleaning the pins and checking each component for itself and didn't find anything that caused it repeatable. For now, I just drilled another hole through the pcb and the case and just pulled it a very bit towards the bottom of the case with a screw. It works but probably not forever.

 

[Michael Tibes]

I haven't taken my W295 apart, but if the connectors between the pcbs are the same as in the V276 then you could try to gently tighten them - very carefully. Putting mechanical pressure on the pcb might not be a long-time solution...

Michael

 

[Whoops]

Putting mechanical pressure on the pcb might not be a long-time solution...

yes , it's better so spend a bit longer and more having more patience in trying to find the loose connection or short.
It could also be a broken pcb trace or a cold solder joint.
I would retouch all the solder joints, it's not a complex circuit so it's easy and quick to do.

I had the problem described  in the past with other units, in one I had a broken pcb trace, when I made pressure on the pcb it worked, I then found the problematic pcb trace and fixed it.
I also had the same thing with a bad solder joint or cold solder joint, touching it with the iron solved it

 

[Tritalos]

Yeah that pcb-pressure-thing only worked for several days. I'm in the middle of exams but afterwards I'll follow your tips, checking for broken lanes, cold joints and the connections between the pcbs.

Thank you for your advices!