Soundstream Class A 5.2 Won't Power Off

[madHD]

The rail+ was reading about -15mV and rail- about 30mV with ground reference on the non-bridging speaker terminals.

[Perry Babin]

OK, post the DC voltage on all of the pins of the 3524.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:

[madHD]

Pin 1: 2mV
Pin 2: 2.57V
Pin 3: 230mV
Pin 4: 0
Pin 5: 0
Pin 6: 3.33V
Pin 7: 2.5V
Pin 8: 0
Pin 9: 200mV
Pin 10: 1.2mV
Pin 11: 0
Pin 12: 11.57V
Pin 13: 11.57V
Pin 14: 0
Pin 15: 11.57
Pin 16:5V

Reference12.3V

[Perry Babin]

What happens if you remove D18?

Be careful, this will disable the protection circuit.

[madHD]

D18 is open. When I removed it I get rail + of 25v and rail - of -25v. I will replace it and go from there. I have a 10 amp fuse on B+ but I was quick about the measurement. Should I expect any other issues now since I will most likely have to order a MBR 150 9747?
THANKS AGAIN.

[madHD]

Also for my learning what is going on here? Why or how did an open diode on the protection ciruit limit rail voltage? Thanks.

[Perry Babin]

If the diode was open, it could not have caused the amp to shut down. Are you sure that you don't mean 'shorted'?

[madHD]

That is what I thought as well but there is no continuity either way across D18 with it on or off the board. I will double check though. Either way I will need to replace it.

[madHD]

I got the replacement D18 diode (MBR150) in. Once again I have no or little rail voltage. I am thinking that either the IC is bad or more likely something in the protection circuit is faulty. Any ideas?

I am not sure how to test the Schottky diodes - MBR150. Brand new out of the package they measure open. Are they gated below a min current or voltage?

[Perry Babin]

They are tested like any other diode but you can expect them to have a lower forward voltage than normal diodes.

Remove C57. Does that make a difference. Leave the diode in the circuit.