Telefunken V672/2 strange noise

[timtom]

I racked recapped several Telefunken v672/2 and one of them has a very strange noise problem.
The overhaul noise level of this card is higher then the other models. I switched the cards on the modules and the noise doesn't disappear.
Also the connecter works fine with other cards.
So the noise must come from the card itself. I replaced the pot with resistors.
But on the card is nothing left then the transformers, 2 caps and 2 resistors.
Could it be that the noise is coming from a defect at the transformer?

 

[timtom]

I racked recapped several Telefunken v672/2 and one of them has a very strange noise problem.
The overhaul noise level of this card is higher then the other models. I switched the cards on the modules and the noise doesn't disappear.
Also the connecter works fine with other cards.
So the noise must come from the card itself. I replaced the pot with resistors.
But on the card is nothing left then the transformers, 2 caps and 2 resistors.
Could it be that the noise is coming from a defect at the transformer?

The noise and crackling came from the input transformer.

 

[TwentyTrees]

The noise and crackling came from the input transformer.

Interesting! Was it a bad solder joint, or had the transformer failed / been damaged?

 

[timtom]

The transformer works but is damaged. It crackles but passes Audio. I replaced the input transformer with one from another working module and then crackling is gone.
I think the winding that is connected to the gain trim and the external resistor has been damaged.
Trying to find a replacement for the input transformer.

 

[timtom]

Would a Carnhill 9045 work in the v672/2 circuit?

 

[rock soderstrom]

Would a Carnhill 9045 work in the v672/2 circuit?

Which Haufe transformer do you need? Original type designation? If you're lucky, I still have one in my drawer.

 

[timtom]

Which Haufe transformer do you need? Original type designation? If you're lucky, I still have one in my drawer.

Originally it’s a RK240 or 6L.5062.003.0.
That would be great!

 

[rock soderstrom]

Tataaa!



Haufe RK240 is a great sounding mic/line in transformer and can handle lots of signal.

Send me a PM for details.

 

[timtom]

Now I have some more modules that have the exact same problem. Pretty strange.
Here is a little sample of the noise.

Does this noise sound familiar?
View attachment v672.mp4

 

[rock soderstrom]

Now I have some more modules that have the exact same problem. Pretty strange.
Here is a little sample of the noise.

Does this noise sound familiar?
View attachment 112268

I hear a weak radio programme and the actual noise, which is quite loud in comparison. Contaminated high impedance areas in microphones sound very similar, I call it the frying pan sound.

What is strange is that this went away with the transformer exchange and now also appears on several other cards. It seems to have nothing to do with the input transformer. Please post the circuit diagram.

 

[timtom]

the “radio” noise is from the mic that was connected to the input, someone talking in the room next door.

Frying pan sound fits perfectly.

 

[rock soderstrom]

the “radio” noise is from the mic that was connected to the input, someone talking in the room next door

ahh,ok!

 

[timtom]

So far I replaced all caps and exchanged the pot with two 1k resistors as the pots also did crackling noise from time to time.

What made me change the input transformer was that even changing the amplifier cards the problem stayed at the broken card and didn’t change to another module. Could also be that some traces are somehow bad.

Also this v672’s are on sale right now and these cards have the later transformers not the original RK240 with the yellow markings.
So they must be changed at some point.

 

[rock soderstrom]

can you trace the circuit with a audio probe or scope? Check where the noise is coming from. Start at the input transformer and then go through the circuit till you find the culprit.

I see tantal caps, check them (or did you already recapped them?). They are highly suspicious. This adjustable capacitor (I think it is C203, in the front of the input transformer) could be the problem too.

 

[rock soderstrom]

Also this v672’s are on sale right now and these cards have the later transformers not the original RK240 with the yellow markings.
So they must be changed at some point.

This can also be from the factory. There were so many variations of these cards.

 

[timtom]

can you trace the circuit with a audio probe or scope? Check where the noise is coming from. Start at the input transformer and then go through the circuit till you find the culprit.

I see tantal caps, check them (or did you already recapped them?). They are highly suspicious. This adjustable capacitor (I think it is C203, in the front of the input transformer) could be the problem too.

All tantal caps are changed as well. the adjustable cap I replaced as well in one card but it didn't change anything.

 

[rock soderstrom]

All tantal caps are changed as well. the adjustable cap I replaced as well in one card but it didn't change anything.

Ok, I see. I think you have to trace the signal through the card to find out whats really going on...

http://diy-fever.com/misc/audio-probe/

 

[GeorgeToledo]

That sound can also be a result of the sub-boards not being fully seated, or having a dirty connection. Maybe a little wiggle to each of the three in the card while checking the output could narrow the noise maker down quickly.

 

[TwentyTrees]

That sound can also be a result of the sub-boards not being fully seated, or having a dirty connection. Maybe a little wiggle to each of the three in the card while checking the output could narrow the noise maker down quickly.

Yes, I was going to suggest this. I had a devil of a time with a V372 a few years back, where I had to clean every pin of every sub-board repeatedly to get it to behave. (And also replace the front panel trim pot, which was somehow leaking DC onto the front panel!)

Edit: and the card edge connector of course.

 

[jokeramik]

Look with an oscilloscope where the noise begins to exist. Then you know where the problem is located.
With these old modules every single part can suffer from problems.
Best regards!