Need help with a Mario Bros coversion - white screen

stanggirl14

Well-known member

Donor 2011, 2020
Joined
Jul 6, 2011
Messages
1,042
Reaction score
35
Location
Raeford, North Carolina
Need help with a Mario Bros coversion - white screen

hey guys,
I bought a DKJR with MB conversion and I'm having trouble figuring out if the board is bad or if it's something else. I get the white screen so many others get and I've searched and tried all suggestions but still no luck.
Right now I'm not getting sound or anything so I can't say if it's playing blind but I am planning to change out the sound board and amp with a known working one to see. And it's a known working monitor with new flyback and cap kit, B+ is dead on 108v

Now all my voltages from the PS to the filter board are good, the only thing I've noticed is that the power from the filter board to the PCB is ok except for the video feeds, they all drop to about 4 volts, everything else stays the same. I've also checked the monitor cable and power is right about 4 volts for R,G,B and sync. I did put in a working PS from my DK cab and had someone mention that being an issue but after checking the #'s the MB is a 7B and the DK is a 7A, should be the same outputs from everything I've read.

I have tried swapping the Z80 chip, removed and cleaned all the chips (sorry, EPROMS I think they're called, not too savvy in this dept), cleaned the board, etc. I have not tested every circuit for continuity but did a visual inspection and can't see any scratches, bad solder joints, etc. I also plugged the PCB into the adapter bypassing the filter board, same white screen.

Any ideas, tips, advice???? I'm still learning and not great with much beyond checking voltage, continuity and soldering. I do not have an EPROM reador or a logic probe or really any idea how to use them but am willing to learn. Thanks!
 
When I have a white screen it is usually because I either didn't plug the board in or harness into the 20ez or something is preventing the PCB from working either it is bad or no power. That's just my experience.
 
When I have a white screen it is usually because I either didn't plug the board in or harness into the 20ez or something is preventing the PCB from working either it is bad or no power. That's just my experience.

yeah, I've checked all my connections and everything, tried 2 different monitors, 2 power supplies, etc. I'd hate to think the board is fried but it's possible. Even cleaned all the EPROM chips and sockets, connections, etc. All caps look fine from a visual inspection anyway.

A lot of what I've read points to the PS which is why I'm curious what the voltage should be going to the monitor chassis. It's possible the cable is bad so I can check it or switch it out and see if there's a difference. Just running out of things to check outside the PCB and looking for some more ideas.
 
That would of been good information to know. If you think the problem is with the power supply, why are you checking the voltage on the video. That's like getting your tonsils checked through your bung hole.
 
That would of been good information to know. If you think the problem is with the power supply, why are you checking the voltage on the video. That's like getting your tonsils checked through your bung hole.

Sorry, should've been more clear, I tested the voltage from the PS to filter board connector and all was good, then checked it on the other side of the filter board and noticed the connections marked in the digram for video were only ~4v so thought maybe it was a filter board issue, then tested the power at the monitor connection and again ~4v, even when I bypassed the filter board they were the same. I was trying to find out if there was a ceramic disc capacitor or something on the filter board causing the voltage differences so I checked what I thought would help rule things out and find the weak link.

Since I saw several posts about checking the +5 and -5 I wanted to make sure mine were ok and they were. Now I just need to figure out if the monitor should be getting the 5v or if it is reduced to ~4v so I can try and rule it out. I'm not great at this stuff so trying what makes the most sense in my mind and from what I've read. I may be 180 off I don't know.
 
Back
Top Bottom