Powerbass ASA 1500.10X

[Dr Zeus]

Ive got this amp which likes to imidiately pop output transistors on the bench even with a low amperage supply. I pulled Q124/Q125 and they were good so i put them back in. I read the Generic Class-D Type 2 page but didnt find much in the way of figuring out why the outputs are going bad. This amp has a total of 8x IRF-FB31N20D. When it pops an outputs, I clip it off the PCB. Test them all shows the serviving ones are ok, only to pop another one upon more power connected.

This is odd/wierd, because I've seen a few of these types of amps with blown outputs which I've clipped off which makes the amp work again - then I replace all the outputs to complete the repair.

This amp doesnt want to play nice?

[Dr Zeus]

Well I guess I didnt check all the outputs correctly. I found another one which shorted and so I clipped it off the PCB. The amp is now working correctly with 5 surviving output transistors.

[timwebb]

i have one i could never get working. i really dont know what the problem is.

[Dr Zeus]

This ASA 1500 actually has provision for another 4 output transistors to make it a total of 12. I guess that would make this amp much like an ASA 2000, but I know the ASA 2000 has more rail caps. I guess I better leave this amp with just 8 outputs. I also dont have enough new units to spare for all 12.

[timwebb]

yea i was looking at that.ill try something when i get this one up.

[Dr Zeus]

Seems this amp is comming back to me after about a week of in-vehicle operation. I'll be opening it up this weekend for damage assessment but already smell the silicon odor. I suspect outputs are burned again.

Should I just replace Q124/Q125, and failed outputs? Is there anything else I should be looking at?

[brandes.cm]

What does the gate drive signal look like? What about the carrier freq? Could a leaky driver cause the outputs to stay on or turn off slower? Voltage spike, soft start not working?

[timwebb]

if u figure something out let me know.

[Perry Babin]

If the low-side FETs shorted, replace Q124/5. If they were not replaced during the first repair, they should be replaced now, even if the low-side FETs have survived. I'd suggest using the MPSW42 and mounting them well off of the board so they don't cook the circuit board. In this amp, you may need to use a heatsink on them since the fan isn't moving any air across them.