Review by Kevin Steele
When I discovered that the Dot Matrix Display (DMD) on my recently acquired Doctor Who pinball machine was starting to "bleed" or blur after an hour or so of operation, I began to panic. New DMD's generally cost around $150, and if the problem was elsewhere in the machine I didn't feel qualified to track it down. My only recourse? A quick crash course in pinball troubleshooting via the Internet.
After a few minutes researching the problem in the wonderful pinball repair guides at the Marvin's Marvelous Mechanical Museum site, I discovered that a blurred DMD display is a common problem on Williams/Bally pinball machines manufactured between 1991 and 1995 (WPC System machines), and is generally due to failing components in the HV (High Voltage) section of the DMD controller board.
Considering the voltages present in the high voltage section (up to 125 volts), and the fact that older DMD displays start to draw dramatically more power as they age and begin to "outgas," it's no wonder that the high voltage circuitry starts to fail.
There are three solutions for this problem (listed from cheapest to most expensive):
As I am only marginally skilled with a soldering iron, and wasn't completely confident that the DMD ghosting problem was actually due to a HV failure, I chose option 2 and ordered one of Pinball Inc.'s DMD-HVP boards from Marco Specialties.
My first impressions were positive — the board had a clean layout and professional appearance (and it certainly looked in a lot better condition than the DMD controller board in my pinball!)
Installation was ridiculously easy — there's only a single photocopied page for instructions, and even that feels like overkill. You unscrew a couple of screws from the top of the existing DMD controller board, mount the DMD-HVP board on top, then move a few cables from the lower board to the new "piggy-backed" board. That's it. The board rests on some plastic risers, so it doesn't interfere with any components on the original board, or block airflow.
Once installed, I fired up the machine and proceeded to play a good two hours' straight of pinball (all in the interest of thorough stress testing, you understand...) Not only was the ghosting and bleeding gone, but the DMD appeared brighter and sharper than ever.
The Pinball Inc. DMD-HVP board has been running in my Doctor Who pinball machine now for over three months without incident. It truly is a plug-and-forget solution to a common problem for Williams/Bally pinball machines, especially for the less technically-proficient (such as myself). Highly recommended.