Alpine MRP-M350

[RiLoWa]

This amp has two IRF5305 and two IRFZ44N on the outputs. I found that one of the IRF5305's is shorted. I then removed all of the outputs to confirm they are ok, which they seem to be. When powering this amp with out any outputs installed, the power LED pulses and it makes a "squeaking" sound.

This is the first Class D amp I have attempted to work on. Does this amp require good outputs to be installed in order to power up correctly OR is there some other problem upstream from the outputs?

The attached picture was taken just after I removed the one bad output.

[Perry Babin]

If the half with the missing output is causing DC to appear on the speaker terminals, it could be going into protect.

[RiLoWa]

With all of the outputs removed, I am not measuring any DC on the output terminal. Should I re-install the three good components and re-check for this?

[Perry Babin]

Is the DC voltage on pin 3 of the upc494 remaining near 0v DC? Or is pulsing towards 5v?

[RiLoWa]

I measure it to pulse between ~81.0mV and ~87.5mV.

[Perry Babin]

Do have a scope?

[RiLoWa]

Yes

[Perry Babin]

Is the upc494 intermittently producing square wave pulses on pins 9 and 10?

[RiLoWa]

Both pins 9 & 10 look identical on the scope, but I wouldn't call it a square wave. It looks more like a dirty sine wave that apears in rhythm with the audible pulsing of the LED.

[Perry Babin]

Set the scope to 5v/div and 2ms/div. Do you see groups of pulses that deflect the trace to about 2 vertical divisions?