Ok!
So following the manual's PSU limits I went on to measure the reference outputs and here is what I've got:
Test Pt. / Ref / MeasuredW961 / -8.6V / -8.599 OK
W9020 / -5.0V /
5.124 OK?? Why positive?W9068 / +5.0V /
0 - SHORT TO GNDW960 / +8.6V / +8.616 OK
W956 / +30V / +29.99 OK
W954 / +102V / +101.8 OK
So I'm seeing 2 issues; the +5v being short and the -5V being inverted
A complete rail failure seems weird as to why would the score operate perfectly fine for a while, but makes sense as to why it would fail following up.
Getting it in failure mode was in fact not easy with the cover off!
I had it run for 2h without the issue appearing
It was only after blocking the fan exhaust that I could reproduce the fault, which led to no change in the PSU rail voltages.
So I guess the next step would be to find that short on the 5V rail; should be somewhere on the PSU area;
Any tips on finding it out? I didn't find any visually obvious sign of faulty component under there the first time
Cheers!
__Yves