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ekorz

Multi Boyz 4 Pi
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I just got a strikers 1999 pcb, and the pcb itself is suuuuper hot on the red. Photos make it hard to show, but this background should be white. All white text is red tinted. The color test is similar (more images here: https://imgur.com/gallery/ikDW6)

I can balance the color by adjusting my monitor to compensate (drop the gain on Red to basically zero, boost the others) and it's certainly playable and looks fine. But basically every other PCB looks great without me fiddling with anything, so I'm guessing something on the PCB is off. Any ideas where to start? Or is this just normal for these pcbs?


zu07sDE.jpg
 
Or is this just normal for these pcbs?
It's not normal.

I have no idea how to help, but I can assure you that's not normal as I had one for almost a decade. It's one of the few shmups I'm actually GOOD at, lol.
 
Not normal at all. Check the RGB lines from the JAMMA edge to see where they're going, would suggest there's a dodgy resistor array in there
 
Not normal at all. Check the RGB lines from the JAMMA edge to see where they're going, would suggest there's a dodgy resistor array in there
Hm, I run into a resitor array "LN1028 IAM". Found this info on KLOV (https://forums.arcade-museum.com/showthread.php?t=271414&page=2). Not entirely sure how to 'build' one of these ladders, but I suppose I could swap a few of them around to test if one or another is not functioning. Other than that, is there a nice way to see if it's dodgy?
 
This "LN1028 IAM" is simply resistor ladders (R2R) used as DAC to convert palette digital bits into analog, many arcade boards use similar custom resistor array.I don't have any board that carries them otherwise I woul have reproduced it.In this case it seems that the component embed also a transistor to amplifiy the signal and bring it to a proper RGB level.
 
Well the part is simple, I just took some readings keeping the ground pin grounded and going from pin to pin for the rest. In order:

gnd, 1K, 2K, 4K, 8K, 16K, 32K, 64K, 128K

Bummer is that all three of mine look the same via my ohm meter. I pulled one to make sure it was the same in/out of the board, and it was fine.

Any reason they would still be suspect even if they read fine? My problem may be elsewhere.
 
I think the transistor inside is gone bad hence the hot red.It's the only party prone to failure, resistors are usually reliable.Probably baes and collector are shorted.
 
@caius

Well then... the part here is just a resistor ladder to my knowledge. Just resistors inside. There is a transistor right next to each one, though. I'll check that part next. Worse case I have a spare parts board arriving soon so I can swap it. Best case I can find a new one

Thanks for the tip!
 
Ah, OK, I misunderstood the post on KLOV, I thought the transistor was embedded in the part.Anyway, check the transistor (I guess a general purpose NPN one like the 2SC1815 or equivalent)
 
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Ok, I think I found one transistor that doesn't behave like the others. Going with this as a replacement, I hope these are standard TO-92 orientation: digikey. Side note, the factory really knocked it out of the park with those center-hole solders yeah?

1c3UwJK_d.jpg
 
You can use other NPN generale purpose transistors like the BC548 and 2N3904 but you have to adapt them since they have different lead assignement.
 
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