Kenwood KAC-PS401m stuck in protection

[Perry Babin]

Some people feel that the damping factor of an amplifier is something that significantly affects the sound quality. The damping factor is specified at the speaker terminals of an amplifier. Beyond that, the DF drops significantly due to the resistance and reactance of the speaker wire. The sigma system greatly (completely?) eliminates the loss in the DF because it takes feedback for the amplifier from the speaker's terminals (not the amplifier's speaker terminals). It's a bit like a 4-wire kelvin system for a multimeter that eliminates the resistance of the meter leads from the resistance reading.

I'm assuming that you have the service manual since it's available online but I've attached it, if not. Following the signal through the circuit, where is the signal lost?

 

[vincegironda]

The collectors of the output devices have 58v dc

 

[Perry Babin]

1/2 should have positive voltage and the other half should have negative voltage.

Did you check for audio through the circuit?

 

[vincegironda]

There's clear audio going into main board from cn1

 

[vincegironda]

Is there anynpoint I can inject audio

 

[vincegironda]

Also the motorised door isn't connected, could this affect operation?

 

[Perry Babin]

I don't know on the door.

You feed signal into the RCA jacks and follow the signal through the circuit.

 

[vincegironda]

I've connected a CD source to RCA's traced signal as far as R102

 

[Perry Babin]

If you take Q101 out of the circuit, do you get audio out of the amp?

 

[vincegironda]

With Q101 out I get audio for about seconds

 

[Perry Babin]

Does the amp completely shut down?

Why does the amplifier stop producing audio?

 

[vincegironda]

I'd doesn't shut down the audio just fades out

 

[vincegironda]

Also the green protection led has continued to flash throughout all the troubleshooting

 

[vincegironda]

So I just noticed, when I apply power the amp produces audio, only the blue power led is lit.

After 3 seconds the green protect ledd kicks in and the sound cuts off

 

[Perry Babin]

So you still have both rail and regulated voltages when you lose audio?

How far through the circuit does it make it when you lose audio?

 

[vincegironda]

Audio traced as far as R102

Still have rail voltage after audio cuts out

 

[Perry Babin]

DCV across R105 when you have audio and after it's lost?

 

[vincegironda]

18v with audio
0v when audio cuts out

 

[Perry Babin]

Does pulling Q221 leave audio playing through?

I'm trying to get the amp working at a basic level to see if we can find the reason it's going into protect. It's likely more corrosion.

 

[vincegironda]

Pulled Q221 audio still cutting out