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DMD Weird Issues re Power

robotgreg

robotgreg

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10 Years
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Aug 11, 2011
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Hi

I have a Babcock DMD display in my Dirty Harry where there are two horinzontal lines out so thought I would get a replacement DMD which I bought off the forum recently. However, when I installed it, there was nothing on it, no power etc so assumed it was faulty.

So I then tried the spare DMD in another machine (Corvette) and it worked fine. I also tried the known working DMD from Corvette in Dirty Harry which again did not work. Therefore something worng with Dirty Harry machine.

I also tried the Babcock display from DH in Corvette and it worked fine too.

So basically, I can only get the Babcock display of any available to work in DH, not any other DMD but the Babcock display will work in any machine.

The other DMDs I've tried are standard plasma as orginially came with the B/W games. Attached pics of both Babcock and other displays been trying.

IMG_20220421_115206.jpgIMG_20220421_115329.jpg

I can only assume somehow in DH, there is not the correct power: 5v or 12v coming into the DMD which the Babcock does not need but the others do?

All connections seem the same between DH and Corvette so is a mystery why unless the power driver board is failing and Babcock does not need as high a voltage. Nothing else a miss with platying the game to suggest any power problems.

Given my inexperience with the eletcrical side and the high voltages to the DMD, not inclined to try to test for 110V etc.

Anyone have any ideas or come across anythign odd like this before?

Cheers
Greg
 
What's your 5v reading? I'm sure those cherry dmds are fussy.
 
Dirty Harry where spare DMD does not work 4.92
Corvette where spare does work 4.94

I'm no expert but would seem surprising if only 0.02 V is maiking the difference.

If it is this marginally lower voltage causing the problem, is there any easy way to increase the output?
 
It’s definitely a weird one. If the dmds work in other machines, my guess would be an issue with the dmd controller board in DH?

If your not confident to test the voltages being supplied to the dmd from J604, have you tried swapping the dmd controller board from DH with another machine?
That way you would know if that’s the problem?
 
Last edited:
Think I've found the reason for this odd behaviour.

Was able to measure the voltages and Pin 2 on DH is only 86V instead of 100V which it is on I500.
 
robotgreg said:
Think I've found the reason for this odd behaviour.

Was able to measure the voltages and Pin 2 on DH is only 86V instead of 100V which it is on I500.
Click to expand...

That would do it. 86v is quite low for pin 2. Off the top of my head I think you want around a 12v difference between pin 1 and pin 2. Anything greater that’s when you have problems.
Readings from game to game will vary slightly due to the power being supplied by the different controller boards because of there age. Low readings is a good indication as well if a board is on its way out.

Time for a new dmd controller board, or see if you can get yours rebuilt?
 
I rebuilt the power on one and it wasn’t hard but the tracks can be delicate as they do get hot in use and crispy with time.
Mine actually had an IC failure so the board is still non working. I bought a replacement version from:https://www.pinballdisplays.co.uk/product-p/dmd089.htm

I was trying to find the pin wiki page where they talk about testing the output of the pins as I know the displays themselves can be less sensitive depending on manufacturers.
 
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