Troubleshooting home theater PSU

[bitwelder]

Hello,

after many years of faultless service, a couple of weeks ago my home theater system (a Philips HTS 3270) suddenly went silent (in the middle of a bigclive video  )
It's usually connected to the TV/Video system, but I tried to play a DVD so to have an internal audio source and it was the same.
Even after setting the volume to max the speakers were completely silent, no hissing/buzzing noise.
After looking at the service manual and the datasheet of the power amplifiers (TAS5342L) my guess was that the amps were probably held into shutdown mode.

So, I checked the power supply board.
Visual inspection: I don't see electrolytics that have bulged or leaked.
On the PCB there are some brownish heat traces only near Q902 and IC902 (i.e. the two switching MOSFETs)

Checking the voltages, I started to find some weirdness.
According to the schematics (in attachment), there are 3 output connectors, 2 of them (bottom right corner) provide +5V, +12V, -27V and stand-by 5V, the other one (top right) has a thick connector to provide VCC (which oddly in some part of the manual should be 26V and in others 34V) for the power amps.

Now, with the device turned on, these are the voltages I have measured:
label -> measured
+5V -> 5.25 V
+12V -> 13.74 V
-27V -> -29.55 V
BK5V -> 5.25 V (i.e. stand-by voltage)
VCC -> 26.01 V

Should I be worried about the voltage differences from the ideal value?
If so, considering that basically all voltages from the 'bottom' switching circuit are a little off, where should start to investigate? The primary section of T901 (i.e. the behavior of the TNY180) ?
What else would you suggest to check?


UPDATE: as I was writing this post using my notes from 2 weeks ago, after having left the unit unplugged and open, I reassembled it to verify the voltages, and while they are still similar, now playing a DVD *does* produce sound. But still I'd like to run a check-up of the unit, and avoid some possible permanent damages.

[mzacharias]

I would say the voltages measured are within the normal range, BUT do not discount the possibility of noise on any given supply line.

This can be checked with a scope.

[bitwelder]

Thanks!

The main reason why I was a little worried about the voltages is that the +12V becomes the VDD for the power amps ICs TAS5342L, and in their datasheet the max value is 13.2 V.

But I'll take a look with the scope