What could be causing those few lines appearing on the DMD of my Lethal Weapon 3? What can I check out?
Turn game off. Then reseat all the ribbon cables . Also could be 'chip creep' on the display board reseat all chips may help. Ribbon cables the biggest offender that I have found though
Also the cpu tells the dmd what to display and when so check your game rom and cables there too. Make sure to upgrade the cpu chip to latest also for best operation or weird stuff can happen if not matched to the display romsets
I just swapped the ribbon cable with TFTC and still have the lines. Then I decided to swap the DMDs and the LW3 DMD still had the lines when installed in TFTC. So that would at least isolate the issue to the DMD. The issue was there when I got the game and upgrading the display ROMs did not eliminate the lines.
The braided ground wire was getting frayed so I made new ground wires that connected the DMD and speakers to the backbox. Didn't help, but needed to be done at least.
Get a new dmd is the only way unfortunately. They cannot be repaired cost effectively.
Selling the game anyway. The DMD never bothered me, but since I was getting ready to sell it, figured I'd see if it was a relatively easy fix.
Could low 12v from on the power supply board be causing the issue? Getting 10.7v using the test points on the board. Getting -14 on the -12v test point. 5v is fine.
Measurements on the P1 connector on the DMD are in parenthesis. You can see pin 1 and 2 are quite a bit low.
P1 pin 1: -110 volts (100v)
P1 pin 2: -98 volts (90v)
P1 pin 3: KEY
P1 pin 4: Ground
P1 pin 5: Ground
P1 pin 6: +5 volts (4.99v)
P1 pin 7: +12 volts (11.9v)
P1 pin 8: +68 volts (70v)
That looks like a shift register problem on the DMD board (on the panel itself, not the controller in the machine). The stray pixels move vertically with the scrolling content, which suggests row bits are not shifting through the column registers properly.
New DMD is mostly likely needed, unless you have a digital logic analyzer and can determine which register is bad. Alternatively, you could simply replace all the registers associated with the wonky columns, which might also fix it. That's likely surface-mount soldering though, which most people aren't equipped to do.
Your voltages are a little off, and the power supply could probably use rebuilding, but I doubt that would cause what you're seeing (especially since you confirmed it by swapping the panel to another game).
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