Tales from the crypt DotMatrixDisplay

blitz_8255

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Display power supply crapped out and after replaceing a couple of transistors and a pair of zeners, my display is all garbled. It is a 128x32 and it looks like a 128x16 that has a bad R95, if you know what I mean. Also I've noticed that the blanking LED comes on at power up but fades out after about 5 seconds.....Any ideas?? U's- 8B-9B??? Going to watch a Pirate game with my granddaughter this evening so I can't play with this untill tomorrow..... Thanks in advance
 
Garbled display is "usually" indicative of a faulty connection between the display and cpu board. This can be due to a faulty cable, bad connection (reseat cable) or having the display cable on backwards.
 
I checked all the connections and reseated them just in case, but they were all good as the display was working perfectly before the supply went south. I'll have to borrow a display and decoder board from another pin to help in the diagnosis.
 
Well I swapped out the display glass and it's looking good! I've got some old ones with bad glass laying around, so maybe someday I'll try to fix it.. as for the blanking LED, wow! It turned out to be a chain reaction of a few parts Q22 & Q30, caused the 7408 at 2J to fry and short the blanking signal to ground which I'm guessing knocked out the 555 at 1C and took out the inverter at U12F. As long as the blanking was down the game kind of functioned except the flippers and the 6 switched solenoids wouldn't work because the
not en blanking signal was wrong and wouldn't fire up 12A and 12B to allowthe coils to fire.
All fixed and playing good, I need a beer!!
 
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