Quad 405-2 Problem

[pborlace]

Hi, I wonder if anyone can help me with this. One of my boards M12565 iss 6
has blown R38. When switched on the resistor glows bright red at which point I switch off! I've read the Quad service data and have checked D5 and D6 which it states may cause the problem. I unsoldered them and they are fine.

I'd be grateful for any assistance with this.

Thanks for looking
Peter

 

[Aldotin]

Hi!

Check output DC offset voltage (meausure voltage on +/- speaker terminal)

 

[cda]

Also check R7 and R8, they are rated very conservatively, and should be replaced with metal oxide resistors of (at least) 1W.

 

[405man]

I would disconnect the DC offset protection by unsoldering the blob next to the output terminal then check the output offset voltage, this should be a few mV. The CD protection triac goes s/c. Then I would check both supply voltages and the supplies to the opamp.

Stuart