Just wanted to report another HD300 saved from the scrapheap by this post.
I had the same symptoms, low to no signal on start up, followed by severe "digital" sounding distortion on all outputs (headphones, inst, bal, USB) and fading volume in and out. Had tried cleaning jacks and swapping cables to no avail.
I disassembled the unit, removed the shield, and on inspection there was no evidence of capacitor leakage. I reflowed all solder joints on U8 and D3 and quickly reassembled without the shield and play tested for over an hour - problem completely solved. The repair took me less than 15 minutes, although I intend to refit the shield which will require some desoldering of the pads.
I would describe myself as an advanced DIY'er with dis/reassembly and soldering experience, but I had no previous experience with SMD components, so was hesitant. I resolved to be very careful and not overheat the tiny SMD components.
I can say if you have this issue, and you have some soldering experience, give it a go, all you need is a CLEAN and FINE tip soldering iron (I used a cheap hardware store unit and had no problems). I did not have any flux on hand and it was fine without. Do not add solder. It only takes a few seconds per pad to reflow, feel carefully for the solder to melt and let the chip cool down between pads. Clean your tip between pads too. I have a desoldering pump at my workshop but it was not at home, that's why I delayed reinstalling the shield.
If you have no repair experience, ask an experienced friend or tech to help.
Removing the shield is the hardest part, you need to heat the solder pads and pry gently with a flat screwdriver, and rotate around the pads repeatedly, with patience.
The HD series is still a great sounding unit, and I was very sad that it failed, as I had really not used it that much despite owning it over 10 years (normally use amp+pedals). I also now own an HX fx and only use the pod at home for late night practice, but I'm glad I can keep doing that.
This forum is a great resource, I hope this post helps at least one other person to save their HD POD
