Hi guys,
I've got a RCF art735-a in for repair which went through a power surge. The half bridge driver IR21531 was fried with the top chipped off. One of the mosfet was shorted along with few other components.

Luckily I had the exact same board with the amplifier section fried. So I started replacing the power supply components from it.
Here's what's happening now- The power supply is not starting up. There's no voltage at VCC pin of the IR21531.

First question- Is it okay to turn on a class D amplifier without a load connected? I'am just trying to check whether the power supply works, and I do not have an input signal applied.
I have attached a diagram of the effected area/ and noted the components changed. I also changed Q6 as it was shorted too (shown in the picture), not sure how its used.

What I have noticed is on start up the supply voltage is dropped across 'the start up resistors and there is no voltage at VCC. Why could this be?
I checked across VCC and COM (of the chip) with diode mode and I get a reading of 0.2V! with probes either way. Could this be a problem?

Thanks in advance for the help
View attachment 189537

 

I checked across VCC and COM (of the chip) with diode mode and I get a reading of 0.2V! with probes either way. Could this be a problem?

Most certainly. suspect the capacitor to ground or the chip.

 

The chip has an internal 15V zener across the Vcc and Gnd pins, so it can run on High voltage with a series Resistor, if you're not getting 15V , then either the resistor is open circuit, the Zener is shorted, or the Capacitor is shorted ..

 

Thanks everyone, I would have to order in a new IR21531. However I was able to get a IR2153 pdip package, I'm thinking of soldering some wires onto it and check whether the power supply works.