DK Jr pcb missing blue

treborlicec

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My DK Jr pcb is missing blue. Verified its the pcb. Hoping it's something simple like a prom. I have a working DK and DK3 pcb if I can swap proms to test. Any ideas are appreciated.
 
My DK Jr pcb is missing blue. Verified its the pcb. Hoping it's something simple like a prom. I have a working DK and DK3 pcb if I can swap proms to test. Any ideas are appreciated.

Prom 2E is used for both blue and green so if your green is all good then it's prob not that. Could be the final transistor that drives blue out to the monitor. (Q11 on the CU PCB)
 
Prom 2E is used for both blue and green so if your green is all good then it's prob not that. Could be the final transistor that drives blue out to the monitor. (Q11 on the CU PCB)

Green is good, so I'll look for a cracked solder joint or trace around q11 and reflow. If no luck I'll order a replacement. Thanks.
 
Did a quick reading. I'm getting .2 on one side of the transistor and .5 on the other. Checked q11 on DK and her .5 on both sides. I recall .4 to .6 is in range for most transistors. Would that reading indicate it's bad or is the tolerance higher?
 
Did a quick reading. I'm getting .2 on one side of the transistor and .5 on the other. Checked q11 on DK and her .5 on both sides. I recall .4 to .6 is in range for most transistors. Would that reading indicate it's bad or is the tolerance higher?

You can't really use a voltmeter to measure the DC levels on each side of the transistor because in reality, the signal is bouncing all over the place (AC), and so the reading you're getting is most likely an average. You could try using the diode setting if your meter has one and make measurements from one of the know good ones (say the one for red for example) and then compare to blue. And you'll want to do this with the game tuned off ;)

Ideally you also want to do it with the transistor removed from the PCB but you may get lucky and be able to detect some shorts/opens where they shouldn't be.
 
I had white disappear on DK3 and I cleaned all the proms and sockets with deoxit and it fixed the issue.

Of course listen up Adam, but it doesn't hurt to give it a try.
 
I tested with diode setting in circuit. Sorry if I wasn't clear
 
I'd still swap the color PROM with a known good one.
ICs don't fail completely (always). One output might be bad, IMHO.
Easy test to be sure.
 
I'd still swap the color PROM with a known good one.
ICs don't fail completely (always). One output might be bad, IMHO.
Easy test to be sure.

Just got back to this. Was at SFGE over the weekend. I swapped 2e from DK into DKJR and the issue looked worse. I put the original 2e back and the issue was gone. This points to a dirty or bad socket. I'll shoot some contact cleaner in there and watch it. If it happens again, I'll replace the socket. Thanks for the tips gang.
 
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