Repair help requested for Class D Subwoofer module of 18 inch 1000W amp module

[Studi-Jo]

Hi,

I am 52, mobile DJ, and studied electronics 20 years ago. After that I never practiced.

I have a DB Technologies DVA S10 18 inch subwoofer, 1000 Watts. On my last gig it started to smell....
Decreased volume and had no choice to switch it off.
Once at home I opened the enclosure and found a complete stuck 18 inch subwoofer, this occured the smell.
Ordered a new one and installed it but when I power the active speaker, without any audio input connected, it immediately and always gives a weird sound
It's not a 50 Hz hum but a higher frequency resonance sound so there is also a problem with the amplifier.

I removed the amplifier module "DigiPro 1000S" and opened it. Surprisely the Power Supply Unit is 3/4 of the module and only 1/4 is the amplifier.

Found online the schematics:
https://drive.google.com/file/d/1LB0oHgbkXONhuaymQSkRktFjN_DAph3A/view?usp=sharing

Because I need the subwoofer cabinet soon for other gigs, I ordered a complete new module but it would be nice if I was able to repair the old one and keep it as a spare. Visually I checked ELCO's and power components but nothing seems broken or smells burned.

Started to check the output of the Power Supply Unit:
New: +13,7 VDC (VDD) -13,7 VDC (VSS) -72,7 VDC (-HV) +72,6 VDC (+HV) -59 VDC (VDR)
Old: +13,7 VDC (VDD) -13,7 VDC (VSS) -98,6 VDC (-HV) +98,5 VDC (+HV) -85 VDC (VDR)
Old PSU gives more voltage to the amplifier MOSFETs but I guess this is not an issue.

The PSU seems OK. How to proceed?
The Amplifier has HEXFET Power Mosfets.
Is it possible to check the state good/bad by unsoldering and measuring? I found datasheets from most important components.

Any ideas or step by step instructions how to proceed would be highly appreciated!
Thanks in advance,

Johan