I reckon rebuild the HV section.
I have a display on my Royal Rumble that does the same thing. Works perfectly for 50 start ups, then goes funny for 3 or 4 start ups then shows all lines lit up and does weird stuff. I took it out and shoved it in another machine and it did NOT do anything weird. But the other display I put in the Royal Rumble started doing the same weird stuff which it had never done before, so I know its a votage issue and I will get Beaky to check the dmd driver board/and the voltages in general.
IF you are going to buy a new DMD, Mad Amusements in the USA have them for $129, postage is around $25 to $35 and the more DMD displays you buy, the cheaper they are and the postage drops as well. A good idea would be to order for ya friends and mates who also want a new DMD display and share in the costs. 
http://mad-amusements.com/product.php?id_product=236
I tried local suppliers, but they cannot match the USA supplier who buys in bulk.
Brett,
On most occasions if you are getting garbage (jumbled lines, or dots all over the place) this is due to a poor data connection to the DMD - ie ribbon cable. Most likely when you've changed the displays out you have reseated the cable giving it a temp fix. I always change out ALL ribbon cables on my games or customer machines to give trouble free operation for years. Greg from RTBB carries most if not all the ribbon cables required for machines.
