Class d amp repair help.

Hey guys i have a US audio m5150 mono block amplifier. It's the same board in the lanzar opti 7000k

The Amp is working however when you power up the Amp and attach a load to the output (to wake up the output) this resistor gets awful hot!! Also if u play a small load on the amplifier the output transformers get extreamly hot. Now this resistor is reading as shorted.
The amplifier was repaired from a constant in protect mode and chip ir2113 was replaced. Now amp works however gets extreamly hot for no reason.

I'll attach a few pics of what parts I'm talking about.
I plan on replacing the resistor but as I don't have a schematic I can't really test other components.

Red circle is the replaced driver chip ir2113
Green circle is of the resistor that gets awful hot as soon as the output is activated.

I might add no other resistors near any of the other drivers or transformers gets hot. It's only the one resistor but all 4 transformers get extreamly hot
(just having trouble uploading photos)
 
Last edited:
Here are the photos. Ic701 is the ir2113 chip replaced. And I think either R668 or 568 is the resistor it's coverd by a bit of black glue so hard to see
 

Attachments

  • IMG_20191022_092027.jpg
    IMG_20191022_092027.jpg
    803.4 KB · Views: 212
  • IMG20191022091951.jpg
    IMG20191022091951.jpg
    725.1 KB · Views: 210
  • IMG20191018193608.jpg
    IMG20191018193608.jpg
    631.7 KB · Views: 200
That resistor may be a resistor that's across the rail to discharge the rail caps. If so, it will get hot as soon as the power supply switches on.

The inductors in many amps are made to order by bean counters and therefore the cheapest possible. Fewer turns of copper and cheaper cores will make the inductors run hot. It's possible but unlikely to have 4 defective inductors.
 
That resistor may be a resistor that's across the rail to discharge the rail caps. If so, it will get hot as soon as the power supply switches on.

The inductors in many amps are made to order by bean counters and therefore the cheapest possible. Fewer turns of copper and cheaper cores will make the inductors run hot. It's possible but unlikely to have 4 defective inductors.
HI perry. I have 2 of these amplifiers and if I check the other one that resistor in circuit reads ohms. Also on the other side of the board of the faulty amp that resistor also reads. It's only this 1 resistor that is shorted in circuit and normal out of circuit.
The Amp was working perfectly fine before the driver chip let go.
No other resistors around the inductors gets hot. Only this 1.
But all the inductors along with this resistor get HOT and I mean burn you're hand hot. But amp works fine?
I can't trace very far from that resistor as the trace goes under the inductor and a bunch of glue.
I may add all this heat comes from simply activating the output by putting a 4ohm load on it. On a 20a power supply. Not playing any music

This board comes apart into 2 pieces. So at the moment just the output side is out.
 

Attachments

  • IMG20191022110024.jpg
    IMG20191022110024.jpg
    547 KB · Views: 58
Last edited:
Have you checked the mosfets ?
The ir2113 is just a gate driver.

Yes they all check out fine. As I said the Amp now works fine and puts out a clean signal on the output. Does not draw too much current it just is running extremely hot. And u can smell burning as a result.
What caused all this mess was a slip of a multimeter probe where the power supply joins to the output. You can kind of see where they slipped pins are a bit distorted.
I found why it was cycling between power and protect. Was ir2113. Replaced that. But now having heat problems.
 

Attachments

  • IMG20191022131635.jpg
    IMG20191022131635.jpg
    385.2 KB · Views: 78
Why do you think the resistors need to be replaced?

It got extremely hot. And also one 22ohm resistor I must have accidentally broke when I was taking the heat sink clips off. It could have been broken previously I'm not sure.
Edit. Sorry I don't think I need to replace the 15k resistor that's getting really hot it checked out fine out of circuit.
But I will need to replace the broken 22ohm one of the legs were snapped off it was mounted vertical on the board
 

Attachments

  • IMG20191022132248.jpg
    IMG20191022132248.jpg
    456.7 KB · Views: 71
Last edited:
You should be able to read 0 ohms from the center leg of the rectifiers to the input legs of the rectifiers.

There should be an identical resistor for the other rail as well.

Contact Lanzar to see if they will send you the diagram.

I get a direct short between the legs on the left(in photo) on the mosfets circled too one side of the resistor getting hot
 

Attachments

  • IMG_20191022_134735.jpg
    IMG_20191022_134735.jpg
    423.9 KB · Views: 81