Background: Purchased a Vs. Unisystem (DK conversion) with SMB installed on the Sub side (with 2A03 CPU and 004 PPU). All working 100%. Looks to have been an early conversion using the factory kit (has the correct nameplate and all). Monitor has some SMB burn so I think it has been an SMB all its life.
Goal: I wanted to add a second game. I purchased the Vs. Interchanger that
@apswann makes, along with a Dr. Mario daughterboard (repro DB with original 2A03E CPU and 003 PPU) from
@joe3693 at pc-10.com via his eBay store. This is the same board used for his Dr. Mario/Platoon dual game kit but I don't give a shit about Platoon so I requested one that was just Dr. Mario without the game selector switch.
Results: Per the instructions that came with the Vs. Interchanger, I moved the SMB CPU/PPU/ROMs to the "Main" side of the board (1-2 sockets), and (attempted to) install the Dr.M daughterboard on the Sub side (6-8 sockets). I installed the Vs. Interchanger, and powered the machine on. As expected the machine booted to the Sub site (as it is a Unisystem), which should have been Dr.M, but I just got a solid blue screen. No game inputs, coin, etc have any effect. No sound, no other video output, no flashing, just solid blue screen. If I hold the P1/P2 buttons down, the switcher pops over to the Main side and SMB is running fine. SMB coins up, plays, all is good. Switch back, and it's just a blue screen.
Troubleshooting steps:
- First, removed the board and tried to further seat the daughter card. Really put a ton of pressure on it. It did "seem" to settle in. Tried again, same results. DB is in so tight I really can't seem to get it out now.
- Checked pin-by-pin continuity from the chip legs of the CPU and PPU on the DB to the underside of the main board.
Results: Have continuity on all pins from CPU/PPU chips, through DB socket, through DB pins, through mainboard socket, to mainboard traces.
Conclusion?: DB is fully seated -- is that a reasonable conclusion? Does continuity imply a "good" connection here??
- Swapped CPUs. Moved 2A03E from Dr.M to SMB and 2A03 from SMB to Dr.M.
Results: Dr.M still boots to blue screen, SMB boots and plays fine.
Conclusion: Dr.M 2A03E CPU is OK. (swapped the back after that test)
- Swapped PPUs. Moved PPU 003 to SMB side and PPU 004 from SMB to Dr.M side.
Results: Dr.M side boots to a green screen rather than blue. Makes sense, since the PPU 004 has the wrong color palette. SMB side boots fine, as expected colors were all wrong (actually kinda cool looking!) as the wrong PPU was installed.
Conclusion: Dr.M PPU 003 is OK. (swapped back after test)
So now what? I
think the DB is fully inserted. I believe I have proven the CPU and PPU are both good. Unless somethign just broke, both sides of the board are good (SMB was originally on the Sub side and worked great, now installed on the Main side and works great). What else would cause the blue screen? Could the ROMs be corrupt/bad? I can pull them and compare the MAME ROMs if necessary, assuming I can read them with the GQ-4X4 programmer. I realized I didn't test without the Vs. Interchanger, but it seems to be working flawlessly to switch and SMB works fine with it installed. I will remove the Interchanger and test just to eliminate it, but I really don't think that's going to be it. Is this just an example of the daughterboard Vs games being finicky? Do I just need to "mess with it" and keep trying? I really don't see how I can insert the DB farther into the sockets, I've literally put most of my bodyweight on it and it's not budging.
I would really appreciate any suggestions or if anyone knows what else the "blue screen" indicates from a potential failed component perspective I would really appreciate some pointers. Thanks!