Energy EW100 / Klipsch KSW10 & KSW12 Plate amp

[Tkeslinky]

I have an Energy EW100 sub that has recently stopped working. It still powers on and the sub even moves around a bit, but with no precision, power, or usable output. I pulled the amp out and noticed several darkened areas on the board, but none of the components appear to be obviously destroyed. Anyway, some pics to show what I'm talking about.
Here is the main area. And pics of the components that appear to be involved. The resistors in the first two pics are in parallel with each other on the board
Here is another area, but much harder to see and the two resistors
What are your guys thoughts? Is this repairable? Any input is greatly appreciated.

 

[Tony Stewart]

Class A/B discrete MOSFET outputs are shown in latest specs.

But Tip31C, Tip32C are NPN, PNP respectively,rated for 100V 3Adc

Check supply voltage Vdc and Vac.
Then check transistor outputs Vdc, Vac.

Big Caps are 1st thing to wear out, which would be evident by lots of Ripple on ?>Vdc+ supply (measure DC & Vac) under load with audio.

Judging by lack of heat sink, I wonder if it actually Class D.

Collectors will have Vcc, Vee supplies and Emitters are outputs.

something but not exactly like above.

 

[Tkeslinky]

Hadn't considered checking voltages while under load. Started to do it last night. Wasn't seeing any ac voltage anywhere in the primary power supply area, but the mains hit a center tapped transformer then immediately go through a bridge rectifier when it connects to the board so I wasn't surprised. Dc voltage was sitting at 61.8. Strangest thing though...I plugged in a source and went to start checking voltages again but the stupid thing is started working again. Plugged it into my HT and it worked all last night so now I'm scratching my head.

 

[Tony Stewart]

Spurious oscillations? These are instabilities that cause full power above hearing range and no power left for sub. THis can occur with Emitter Follower designs into a capacitive load with ESL, such as V regulators.

maybe.. or poltergeists

 

[Tkeslinky]

Well, I continue to be flummoxed. Over the last 3 nights the sub has performed admirably...for a low cost, low power 10" anyway. It makes no sense given how it was acting previously. I appreciate the input at any rate. If it acts up again I'll check back. Just awful hard to fix a problem when I can't duplicate it at this time.

 

[KeepItSimpleStupid]

Some things, +-Supply,
Voltage across C4 -- A multiple of Vbe, not zero.
Zero will result in a cold idling amp. and crossover distortion.

Monitor Voltage across R2 and R16 with no input. This is measurement for an adjustment by P1. To high, thermal runnaway sets in.

C6 sets the low frequency response.

 

[tomizett]

If the old take-it-apart-and-put-it-back-together-again trick worked, it might be something "mechanical", like a bad connection or dry solder joint.
Try running it up with some signal and prodding it about with a plasic biro or something, see if you can make it fail. You might also like to just re-work some of the solder around the heavier components.