Behringer PMP980S - Left Channel Down

[GCG]

Hi everyone, new member here!

As the title says, I have a Behringer PMP980S with the left channel down (LPA2400). I did a preliminary troubleshooting and found out that the 9140 had the same voltage between drain and source (-HV). Further testing seemed to point it was in short, which was confirmed.

I replaced it, but although the MOSFET is fine now, it still has the same voltage between drain and source, as before. I have read that sometimes the 18v zener (D55) gets damaged, but it seems fine.

Any help will be greatly appreciated.

[Jazz P Bass]

Did the 9140 show a short from D to S when it was removed?

The 140 & the 9140 are commutators that switch in the HV when needed.

There are a number of low value resistors that go open on a failure.
Test them all.

I have a feeling that other components are blown causing the voltage oddity.

LPA2400.pdf

[GCG]

Thank you for your reply and the attachment.

Yes, the 9140 was in short. It shows 0.4 ohms between D and S after removing it.

I checked Zeners D55 (18v) and D7 (15v) and they are clamping the right voltage. I'll check the resistors you mentioned. Any other ideas?

Thanks again!

[GCG]

OK, I did what you suggested, but I couldn't find any bad component

I took some readings on the MOSFETs to compare the good and the bad channels:

Bad Channel (L)	Good Channel (R)
9140	9140
S: -73.4v	S: -61.3v
D: -73.8v	D: -73.8v
G: -72.4v	G: -65.2v
140	140
S: 39.1v	S: 39.0v
D: 74.4v	D: 74.4v
G: 38.4v	G: 38.4v

Could this be caused by T5 (SAP16P)? What do you think?

Thank you for your help.