ADS a/d/s Braun PQ20 with no output

[gisewhcs]

Hello folks!

I have a PQ20 lying here that had one bad driver IC (µPC1270H).
After replacing the bad one i've got no output on either of the four channels.
The supply is working fine, I've got the +/-30V, none of the outputs is shorted and I've got my signal and all supply voltages at the input of the driver ICs.
I just saw that the IC can be muted on pin 3, I believe.
Is there a part, common to all ICs that might fail and mute them all?

Thanks in advance!

Julian

[Perry Babin]

Does this amp use pin 4 of the driver IC as the input for 2 channels and pin 5 as input for the other 2 channels?

I don't think there's a common mute line that feeds all channels. The mute terminal probably goes to ground via two series connected resistors. The resistor that connects to ground probably has a capacitor in parallel with it. I don't know if the capacitor could cause it to be muted if it's leaky. You could measure the DC voltage across the two resistors to determine if the current flowing through the two resistors is the same.

[gisewhcs]

This amp has one IC for each channel.

And as you've mentioned it has, as far as I saw, that RC-net you've mentioned for each channel.

I will take some more measurements tomorrow!

Thanks for your hints!

[gisewhcs]

So, I found the problem.
There is a "Protector IC", µPC1237HA in it.
That one just failed, don't know why.
Changed it and the amp plays fine again!