2 Monoblock Class Ds Not Working, I'm Lost

[D132]

I still get the partial LED at around half volume on the headunit, no gain
LED reads 0.42v now

 

[Perry Babin]

In 1/2 protect, are the outputs of US3 still very near 0v?

With the black probe on the ground terminal of the PS driver board, what is the DCV on the anode of the protect LED?

On the cathode of the LED?

 

[D132]

US3 pins 1, 4, 7 are/are close to 0v (all below 0.1v, read at black probe primary ground)

Anode is 0.16v
Cathode is 0v

All read in half protect

 

[Perry Babin]

What's the DC voltage directly across the resistor RS30 on the PS driver board?

 

[D132]

.07v in half protect
.003v in normal idle

 

[Perry Babin]

Could you be getting light contamination that simply makes it look like it's lighting up?

 

[D132]

I am 100% sure it is not
I have seen it on with no lights in the room before, and i hear a very slight change in fan speed when it goes into half protect.
Also it buzzes most of the time in normal idle and the buzzing goes away in half protect.

 

[Perry Babin]

Do you see a change in the drive signal (pins 9 and 10) of the other 494 when in half protect?

 

[D132]

Multimeter or scope?

 

[Perry Babin]

Scope.

 

[D132]

9 and 10 showed the same for everything on both chips
Chip circled in red showed only some noise in normal idle

Half protect showed some oscillation of some sort

Circled in blue showed nothing in half protect but I’m also not sure if I was properly making contact with it

 

[Perry Babin]

Do you see excessive noise on the B+ or remote terminal of the PS driver board?

To check this, solder a short piece of wire to the ground terminals of the driver board and use the short grounding lead that clips onto the end of your scope probe to connect that that short wire. Don't let it move around to contact anything else. Then probe B+ and remote (and any other pins) to see if one is noisy.

Check these as the amp goes from normal operation into protect.