WARNING
There are very high, lethal, voltages (over 300V) generated within the power supply which maybe present even if the mains power is disconnected.
Our Humax Fox T2 Freeview PVR stopped working; there was no circle of light around the power button and there were no signs of life anywhere else.
I checked the power switch, the fuse in the plug and checked that the socket was live: all were working. So I took the box to bits and tuned in to the Hummy.tv forum where I read that the snubber circuitry often fails. This is what I found when I checked the power supply: (Hover over the thumbnail for larger image)
I was concerned that if the snubber circuit had failed then the device which it was supposed to be protecting might have failed also so I tried, unsuccessfully, to find a circuit diagram for the power supply so that I could assess the situation. Because I couldn't find a circuit diagram I traced out the circuit from my power supply. You can see it here.
Clearly I needed a new C3 but I determined that C2 and the ultra fast diode HER108 were still viable. I ordered a new C3 from Bitsbox. The original was rated at 1kV but Bitsbox had a 3kV component so that's what I bought You can see the item here
From the circuit diagram it's clear that the snubber circuitry is protecting the STR-W6252D PWM switching regulator's power MOSFET. However, according to the datasheet, the drain-to-source breakdown voltage for the MOSFET is 650V minimum. So, fingers crossed, it might have survived.
It turns out that I am lucky; I replaced C3 and our Hummy is worlking fine again. Whew!