Simon,

I’m afraid your power supply is failing. The fact that your HD621 came back to life 20 minutes after being switched on tells me that. This is exactly the same symptom I had on my own HD621 six months ago – shortly afterwards it failed completely. Whilst yours appears to be working ok now, it too will fail completely soon. Don’t wait for this to happen as it could damage other parts of your HD621.

I doubt that any electrolytic capacitors have been “reformed” – but you can do a simple check if you like. Turn your HD621 off at the mains, wait for an hour then switch it back on again. If it jumps back to life immediately then perhaps they have. But if it doesn’t come back on immediately this confirms that the PS is failing.

The good news is it's very easy to replace the PS. If you’re comfortable lifting the lid yourself it is a simple component swap. The only special tools you will need are a Torx screwdriver (T10 from memory) and an electrical multi-meter. Both are readily available for modest prices if you don’t already have them.

Just unplug your HD621 from the mains (that’s important!), remove the Torx screws to get the cover off, unscrew the power supply cage and the earth lead, unplug the old power supply and drop the new one in its place. Then put everything back together again the same way you took it apart. Incidentally, the voltages come pre-set although the 5V setting is adjustable and it would be good practice to check this.

If you’re not comfortable repairing it yourself, Mr TechGuy should be able to do it at a cost effective price.

BTW, I just did a quick check on-line; the correct PS - ECM40UT31 - is available from uk.farnell.com for £42.34 delivered or from uk.rs-online.com for £44.06 delivered.

Good luck whichever route you choose and if you need more help then just PM me.