musysic mu-pm8c - need schematic for output section

[MichaelNuzum]

Hello all,

I have an unfamiliar unit on the bench today. Brand is musysic. Model is mu-pm8c. It is a powered mixer. The owner, from what I can tell, plugged a bass amp output into the powered output of the board, saw sparks, and now has no output at the powered speaker out. There is signal at the headphone outs, so it looks like the front end survived without damage. The power output section, however, has blown fuses. Possibly a few blown resistors. Probably more.

I put new fuses in and fired it up on the variac, and it gets very hot very quickly at the output transistor heat sink with no signal being applied, so something is going crazy with the current consumption. I'd love to find a schematic so I can focus on pertinent components and not fire it up any more than I have to, I don't want to blow more stuff up.

I have looked around the net and used the search function here, but have had no luck finding a schematic for this unit. It really isn't too bad at all as far as accessibility for repairs, but I can't find any documentation, and I don't trust my skills with transistors to just fly blind on this one.

Any help would be immensely appreciated. Thanks in advance.

[nickb]

$200 new. Looks like competition for Behringher.

Have you asked the manufacturer? info(you know what symbol here)musysic.com

[MichaelNuzum]

Yeah, I tried contacting them a few days ago, but hadn't heard back. So I figured I'd try here while waiting.

I know it isn't much of a unit in the grand scheme of things, but it would mean the world to this kid and his band (as well as save some junk from the landfill for now) if I could suss it out and get it up and running for a reasonable price. If not, no great loss, but I figured I would at least give it a try for him.

[nickb]

Well it will do no harm to take the top off and look at what you have there. It's almost certainly class D and there's a very good chance that it uses an off the shelf driver / modulator chip. Once you've identified that go get the datasheet and any application notes and you will often find a reference design. There's a good chance the what you have follows the reference design and that should give you something to go on. If you're lucky just the output FETs will be blown. Take a look at what is connected to the gates and check for any bad components there. If the gates are not transformer driven I'd be strongly inclined to the replace the driver too.

I take the power supply is still OK.

PS: a nice piccie of the board might help.