a couple years ago I bought a couple mr. do boards from the same guy off ebay who sold them as "unknown"
of course they arrived broken and I just recently started looking into the problem again.
one actually seemed to work (completes self tests OK apparently and seems to work in demo mode...) however the problem is.. the game will only display a single video frame (for 2-3 seconds) then go blank for about 20-30 seconds. then display another frame of video... on and on..besides that it seems to work fine. (I can coin up, put it in test mode etc, but the single frame followed by 20-30 seconds of nothing makes it impossible to play obviously.
the other boards was completely hosed.. missing chips, wouldn't do anything at all.. (cpu address/data bus not even moving) after replacing the crystals and associated clocking circuitry along with a missing ROM.. I get it up and it does the EXACT same thing as the first board. ("freeze frame single frame image" then blank for 20-30 seconds)
Now I"m pretty good with digital logic troubleshooting and troubleshooting CPU architecture issues, but I am horrible with analog and video stuff. anyone have any ideas on these. My guess is whomever owned the boards probably plugged them both into a faulty rig that somehow fried the same video circuitry.. but i am not sure where even to start looking on this. As I mentioned the the CPU system components seem to work Ok but it has to be somewhere in the video circuitry or possibly the timing/blanking circuits?
of course they arrived broken and I just recently started looking into the problem again.
one actually seemed to work (completes self tests OK apparently and seems to work in demo mode...) however the problem is.. the game will only display a single video frame (for 2-3 seconds) then go blank for about 20-30 seconds. then display another frame of video... on and on..besides that it seems to work fine. (I can coin up, put it in test mode etc, but the single frame followed by 20-30 seconds of nothing makes it impossible to play obviously.
the other boards was completely hosed.. missing chips, wouldn't do anything at all.. (cpu address/data bus not even moving) after replacing the crystals and associated clocking circuitry along with a missing ROM.. I get it up and it does the EXACT same thing as the first board. ("freeze frame single frame image" then blank for 20-30 seconds)
Now I"m pretty good with digital logic troubleshooting and troubleshooting CPU architecture issues, but I am horrible with analog and video stuff. anyone have any ideas on these. My guess is whomever owned the boards probably plugged them both into a faulty rig that somehow fried the same video circuitry.. but i am not sure where even to start looking on this. As I mentioned the the CPU system components seem to work Ok but it has to be somewhere in the video circuitry or possibly the timing/blanking circuits?