Love HH, I've done every mod to this machine of mine now and it runs very nice. 

I rebuilt the original power supply, but thought that the 5v wasn't still good enough and ended up buying a replacement from greatplains which is an excellent product.

Upgraded the original pop bumper boards but ended up replacing them with rottendog, which are excellent.

Bought the rottendog driver board for it, it too suffers from grounding problems and originally wouldn't work in my machine.  Got it to work, still prefer the original driver board thou the rottendog seems to give the solenoids an extra punch during play.

Bought the Ni Wumpf cpu, didn't like it so the original went back in.

My brother owned an HH a few years ago, it had it's fair share of problems so when he decided to sell it, I passed up the opportunity to buy it because I thought it was too much trouble to fix it. There was nothing wrong with the playfield, cabinet or BG, it was only electrical problems. Now I know that all of the problems could have been fixed and I regret the decision not to buy it. Hindsight sucks  

Matthew