So I have 4 sound board related problems on my Checkpoint.

1. A hum through the speakers which follows the lamp matrix, which is most noticeable during attract mode. Mine is not consistent though. It usually starts very quiet, then after some time, gets quite loud. Then it usually just stops or goes back to being quiet after even more time.

2. The hum, which it looks like GDonovan has come up with a nice solution for. (Just sent you a PM!)

3. Occasionally, but not very often, the sound will get brighter and loose the low end (on all channels) as if someone was turning a highpass filter on the sound and increasing the cutoff frequency. The sound will get very tinny, and then suddenly go back to normal.

4. The soundboard messes up my DMD. This is the one that is the most frustrating. All of the other problems I can deal with. The DMD score screen is the first to go. It usually gets garbled or just goes blank. Sometimes the other DMD images are garbled, but usually not. Usually the garbling happens in time with the music changes. (Very obvious at the start of a new game. When you quickly flip through the different music choices, it screws up the DMD each time it changes). For the longest time, I thought this was a DMD issue, however in trying to isolate the lamp matrix hum (by unplugging the soundboard), all of the DMD issues instantly went away (and stay gone). DMD voltages are all correct. As soon as the soundboard is plugged back in, the DMD goes haywire.

Voltages measure at +11.98V (stays consistent at power board) (drops to 11.6 during use only at the soundboard), +5V, -15V (at soundboard and power board). Is the -15V out enough to be causing some of my problems?

So I'm wondering if the 12V that powers the soundboard is affecting the 12V that controls the DMD. There is a voltage drop at the soundboard on the +12V when the soundboard is in use, but I'm not seeing that voltage drop anywhere else (but it could be that my meter doesn't react enough to pick it up).

I've double checked all of the grounds. All of the boards have the screws and they are tight. Floating the soundboard only made the background hum worse, so I put the screws back in as normal.

Any thoughts? The DMD issues are what puzzle me the most, and in reading the 13 pages of this thread, I didn't see anyone else who had that problem.