PPI DCX1000.1 Dead Chirps

[mbates14]

PPI DCX1000.1 class D amplifier. The power supply chirps. All output transistors and power transistors test fine. no shorts. Guy said he accidently reversed the polarity on the positive and negative power input to the amp, seen a spark and went oops. lol.

So now, it does this. has SG3525 regulator PWM system, along with alot of surface mount transistors, resistors, and a few scratched off chips i guess to protect against cloaning. I checked everything i could, the rectifiers, all the caps for high ESR, checked the + and - 15V regulator transistor circuits, and all the IRF3205s in the power supply. comming up empty handed here. All it does is chirp. using the fluke 70, i can see the rails trying to come up on each chirp, until it hits about 25V or so, it makes a louder chirp and goes all the way back down to 0, and slowly tries to work the voltage up again with each chirp. Cant figure this one out.

Any help would be appreciated.

[Perry Babin]

Do you get any significant DC on the center legs of any of the output transistors?

[mbates14]

dont think so, i believe its the same as the rails. I was watching the rails from the outputs of the rectifiers, and the output transistors was giving me same exact readings. Also one of my outputs shorted D to S, from trying so many times, i had to remove it from circuit.


I think there was more IRF9640s than IRF640s in this amp

[Perry Babin]

If you get rail voltage on the center legs of the outputs, that's significant. You need to check this and post what you find.

Were the transistors clamped when the output failed?

[mbates14]

Yes. I never power any amp unless the heatsinks are in place. i learnt this mistake once years ago and aint doin it again.

[mbates14]

Did a quick measurement, it shot up and over 13V before another FET went south, so i had to cut it off.

[mbates14]

With the old bad output, and now new bad output out of circuit, the power supply only chirps 3 times and then it quits... speaker relay clicks on, so now the power supply is holding. it still chirps every time you cut it off and back on, but only for 3 times.

Then after a little bit, the rest of the outputs just went on just that channel. The other channel is fine. no swinging voltages or anything on the center pin. and no shorts.
Whats odd, is the now bad channel, all the outputs were fine until now... lol...

[mbates14]

Also to add to the above, only the 9640s went in the channel, had 2 out of circuit, with 2 remaining. last 2 eventually shorted while the amp was on with relay engauged. The 3 IRF640s in that channel are still fine.... it has more 9640s than 640s. why?

[Eva]

IRF9640 is a P-channel MOSFET and has an inherently higher drain to source resistance when turned fully on. More devices in parallel are required to match the N-channel ones.

It seems that there is a fault in gate drive causing both halves of the output stage of that channel to turn on at the same time, or the output inductor has shorted turns, or something is wrong with the modulator causing the channel to oscillate at the wrong frequency (usually at output filter resonance).

The power supply is probably shutting down in response to this fault (usually DC at the output or overcurrent detection).

[Perry Babin]

Pull all of the outputs out of that half of the amp and look at the gate signal. It should swing ~10v from the rail. The waveform should be relatively square. It should look similar to the attached waveforms. The top and bottom of the waveforms should be approximately the same as the rail voltage.