Help with class D repair please

xokia · 22nd October 2004, 03:07 PM

I have a class D amplifier I am trying to repair. It just keeps blowing fusses. I replaced one of the transistors on the power supply side because it was leaking current when the amp wasn't turned on. The PWM is suppossed to be a fixed frequency varying duty cycle design. I have this this regulated to 12V 1.5 amps. When I turn it on the voltage goes down to 7V because its current limited. I can get it to start switching but at about a 50% duty cycle. I don't have a schematic for this amplifier so I am working in the dark here. Any suggestions.

demons_wing · 25th October 2004, 05:31 PM

hey there..im no expert, but you are right..it is current limiting..try check and see if the reference hiccups..also check the output rectifiers on the PSU...there has to be a leaky/SC semi somewhere...

xokia · 25th October 2004, 09:45 PM

I'll try the output rectifiers. This is really bugging me because I know its something simple. Its like there is a dead short after the switching power supply. With no schematic its a real pain.

demons_wing · 26th October 2004, 03:22 PM

it could be the PSU too...maybe you can try to remove the power amplifier and test the power supply...since its a switcher, it needs a load to start..measure the input resistance of the ampl and use a high power resistor of the same value to load the PSU...then try and see if the psu is limiting...atleast this way you can eliminate one possibility

22nd October 2004, 03:07 PM	#1
xokia diyAudio Member Join Date: Oct 2004	Help with class D repair please I have a class D amplifier I am trying to repair. It just keeps blowing fusses. I replaced one of the transistors on the power supply side because it was leaking current when the amp wasn't turned on. The PWM is suppossed to be a fixed frequency varying duty cycle design. I have this this regulated to 12V 1.5 amps. When I turn it on the voltage goes down to 7V because its current limited. I can get it to start switching but at about a 50% duty cycle. I don't have a schematic for this amplifier so I am working in the dark here. Any suggestions.

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25th October 2004, 05:31 PM	#2
demons_wing diyAudio Member Join Date: Apr 2004 Location: BC	hey there..im no expert, but you are right..it is current limiting..try check and see if the reference hiccups..also check the output rectifiers on the PSU...there has to be a leaky/SC semi somewhere...

25th October 2004, 09:45 PM	#3
xokia diyAudio Member Join Date: Oct 2004	I'll try the output rectifiers. This is really bugging me because I know its something simple. Its like there is a dead short after the switching power supply. With no schematic its a real pain.

26th October 2004, 03:22 PM	#4
demons_wing diyAudio Member Join Date: Apr 2004 Location: BC	it could be the PSU too...maybe you can try to remove the power amplifier and test the power supply...since its a switcher, it needs a load to start..measure the input resistance of the ampl and use a high power resistor of the same value to load the PSU...then try and see if the psu is limiting...atleast this way you can eliminate one possibility