Class D amp basic troubleshooting, help needed

[elnaldo]

Hello,
Could somebody be kind enough to show me a basic step by step test procedure to diagnose a class D power amp not emitting sound? I mean the basic A-B-C tests with this kind of amps.

It's a powered mixing console, behringer PMP5000.

I've read it shares the power section with this model, PMP1280
https://www.electronica-pt.com/esquema/audio/behringer-audio/behringer-pmp1280s-15958/

The amplifier was running in Bridge mode with 2 speakers connected, when the user manual says "never use the OUTPUT A connector" when in bridge mode.
thanks very much.

 

[elnaldo]

Hello. I'm tracing the signal, found that I have a signal at the Mosfet Gate Driver ( IXDD404) inputs (518KHz), but nothing at the outputs.

Does this points to the IC itself, or could the IC be OK and the problem be at the Mosfets? They don't measure shorted in circuit.

The IC has a "enable output" pin, but it's biased properly. (in low state it mutes the output, but it has +8V)

This is the signal at the IC gate driver input:


and this is the signal at the IC output:

 

[triode17]

It looks like the IC failed. i am more familiar with Sw. Mode Power supplies but its the same principle.If the FETs aren't shorted, its usually the driver IC.

 

[elnaldo]

Thanks. I'm searching for a replacement locally, no luck yet.

 

[elnaldo]

Hello. Replaced the driver IC, no change , I don't have sound or any switching at the IC output.

Can I test a class D amp without the output Fet installed?

What I see is that I have a very small voltage swing at the IC input, just 240mV, not full Vcc. Perhaps the output is fine and the problem is before the IC...

schematic attached: