Behringer PMP980S no output

[chuckozzie]

Hi everyone first time poster.
I have got a Behringer PMP980S that I think the power amp is gone in it.
I bought it very cheap from a pawn shop as it wasn't working.
I could hear the protection relay clicking in when I power up.
So I disconnected the the power amp module -- LPA2400 from circuit and the unit fires up ok, with all the lights on in the mixer.
I have successfully put a signal through all of the mixer channels and used all the effects etc and it seems the mixer part on the unit works fine.

So I think the power amp is sus.
I have taken the heat sinks off the mosfets to examine the board, but I can't detect any burn marks or scoring.
It does look like someone has had a go at replacing some components (mosfets) because the soldering is not up to the same standard as the rest of the board.

So I would like to get a schematic to help me find the fault, if someone could help out.
I don't know much about class d amps but I have been reading as much info on them as I can.
I have an electronics background and all the tools, CRO etc so I don't mind having a go but it is really hard without a circuit diagram.

thanks
chuckozzie

[Jazz P Bass]

You can usually find the bad mosfets because they short.
The 18V zeners sometimes take a hit.
And the driver IC's can go too.

[Jazz P Bass]

LPA 1180 schematic

I wonder if the LPA1180 is even close?

[Enzo]

Nah, that's the small one. The 2400 is a stereo power amp for a full size box mixer.

I think the LPA2400 is an analog version of the digital HCA2400

[chuckozzie]

Thanks for the replies.
The lpa1180 schematic is not close to what I have.
The LPA2400 has 100v, 40v and 15v rails on the power amp.
It has the SAP16P Mosfet ( Darlington config I think it has 5 legs) and the Mosfet 140 driver and a Mosfet 9148 that I don't know what it does.
The problem I have is that whatever the fault is it's stopping the SMPS from powering up.
Should I try and isolated the various voltage wires from the SMPS to amp in turn to see what power bus is taking the SMPS down and then investigate the devices on that rail.
Thanks in advance
ps-- circuit would still be nice thou!
chuckozzie

[Enzo]

Nah.

The SAPs are bipolars, and are your main outputs. The 140 and 9140 are commutators, they switch in the higher voltage supply rails as needed.

The SMPS works without the LPA? SO look to find if one chanel is blown. Got shorted outputs or commutators? I don't recall here, but most Behringer outputs of the era have crowbar triacs on the output jacks. Disconnect the wires from the LPA to the Speakon jack board. Now, is hot shorted to cold on any of the speakons?

Here is a trick, clip ohm meter to the hot output wire of the amp out. Now measure for continuity to the power rails. If there is continuity to any of them, you have a shorted device. And don;t forget, a power rail may not be shorted to ground, but if it is shorted to the other power rail, that is just as bad.