Bally Solved Doctor Who (Bally, 1992) Dot Matrix Problem

[mwrussel]

Hello,

I'm trying to trouble shoot a 1992 Doctor Who display issue. The dot matrix display is very weak. Upon startup, only about 1/3 of the screen lights up with it filling from the left and right lower corners. If the machine is allowed to sit and warm up for several hours the display might eventually fill to approximately 95%. I replaced the Dot matrix board but that didn't fix the problem. I've checked the connectors which are old but none are charred or burnt, all look clean and shiny.

I thought the transformer for the machine may be weak, but all other aspects of the game seem to function normally.

Any advice on where I would check with a DMM for proper voltages or other thoughts would be greatly appreciated.

Thanks,
Mike

 

[spalmer]

Check voltages on the connector on the left hand side of the DMD itself.

Pin 1 should be -110 to -130
Pin 2 -98 to - 113
pin 3 N/A (key
pin 4 and 5 ground
pin 6 + 4.9 to + 5.2
pin 7 + 10 to + 14
pin 8 + 58 to + 68 volts


Check dirst with the connector hooked to the DMD. If any are off, disconnect the DMD and retest. If they return to normal DMD is bad.

 

[mwrussel]

Thanks for the quick response. I checked the DMD as you suggested. All the voltages were within the ranges you listed. Am I correct in assuming that means they are receiving the correct voltages and therefore the DMD is bad?

I really appreciate the help.

Mike

 

[spalmer]

Without a visual inspection, I would say that is correct. Do you have another display you can test with.

 

[mwrussel]

I do. My other pin is a cftbl, I believe they are the same model but I'll check

 

[mwrussel]

I swapped out the DMD's between Dr Who and CFTBL and the display worked great in Dr Who. So it does appear to be the DMD itself. I put the lower quality one back in CFTBL and it seems to work a little better than it did in doctor who, but still obviously faulty.

Thanks for helping me diagnose the problem.

Do you have a recommended place to purchase a new DMD or are most online places the same?

 

[spalmer]

I use these folks. They are my prefered vendor for most everything.

http://www.marcospecialties.com/pinball-parts/DMD32

 

[gwhorto]

U can get them for about 140.00 if u look around on the net.