What's new
By:

Dodonpachi playing blind

hrvat9

hrvat9

Enthusiast
Joined
May 12, 2017
Messages
253
Reaction score
78
Location
Mississauga, Ontario, canada
I got a Dodonpachi board here that looks like what I would assume is a sync issue? Not sure but does anyone have any clue? Also if I cycle the pcb it’ll go from a white tearing screen to a blue tearing screen to a green tearing screen. The main cpu chip has been socketed for some reason also by someone else

https://streamable.com/8ur70c
 
No game sounds, so I'd assume it's more than that. If it were just a sync issue the game would be playing in the background. Probably start with making sure that that socketed CPU is actually good (and the socket's good).
 
Yep, it looks like the 68000 CPU is crashing during bootup and the watchdog is rebooting the board after.

1) If you have a multimeter, set it to continuity and check the connections between each pin of the 68000 CPU to their destination. You may have a damaged trace or bad connection with the CPU socket.
2) If you have an EPROM programmer, dump the EPROMs located at U26 and U27 - those hold the 68000 CPU code - and compare them against MAME. One of them may be corrupt.
3) Try a different 16mhz 68000 CPU. I believe this one is a match for the one on the board currently: https://www.ebay.com/itm/395963418989
 
ShootTheCore said:
Yep, it looks like the 68000 CPU is crashing during bootup and the watchdog is rebooting the board after.

1) If you have a multimeter, set it to continuity and check the connections between each pin of the 68000 CPU to their destination. You may have a damaged trace or bad connection with the CPU socket.
2) If you have an EPROM programmer, dump the EPROMs located at U26 and U27 - those hold the 68000 CPU code - and compare them against MAME. One of them may be corrupt.
3) Try a different 16mhz 68000 CPU. I believe this one is a match for the one on the board currently: https://www.ebay.com/itm/395963418989
Click to expand...
So I checked the roms and they both came up on the romident website.

I also did check all the pins from the cpu to make sure they’re all going somewhere.

I have a Motorola 68000-10 as a spare and I tried that also and nothing :(
 

Attachments

  • image.jpg
    image.jpg
    154.3 KB · Views: 57
  • image.jpg
    image.jpg
    163.8 KB · Views: 61
I also noticed that the first “038” custom had been reflowed so I went to check that over. I found 4-5 pins shorted and cleaned them up but that probably has nothing to do with the cpu
 

Attachments

  • IMG_1292.jpeg
    IMG_1292.jpeg
    143.6 KB · Views: 65
  • IMG_1291.jpeg
    IMG_1291.jpeg
    134.1 KB · Views: 61
  • IMG_1289.jpeg
    IMG_1289.jpeg
    109.4 KB · Views: 67
  • image.jpg
    image.jpg
    171.4 KB · Views: 70
Yay for progress! Now you can write the CPU off your culprit list.

The all white screen is interesting. The DDP hardware draws three tile layers and a sprite layer. It looks like the top tile layer (FIX layer for high score and stats display) isn’t reading any data so it just draws all white (FF values) and covers up everything underneath.

Check the U62 ROM - it drives the FIX layer. If the ROM dumps clean and matches MAME then check the connections and traces for that ROM and the custom graphics chip it’s connected to.
 
ShootTheCore said:
Yay for progress! Now you can write the CPU off your culprit list.

The all white screen is interesting. The DDP hardware draws three tile layers and a sprite layer. It looks like the top tile layer (FIX layer for high score and stats display) isn’t reading any data so it just draws all white (FF values) and covers up everything underneath.

Check the U62 ROM - it drives the FIX layer. If the ROM dumps clean and matches MAME then check the connections and traces for that ROM and the custom graphics chip it’s connected to.
Click to expand...
If I cycle the pcb , the backround will also go blue , or a purplish colour. Could I send you my original rom files ? I don’t know how to plug them into mame to verify if it’ll do the same thing

I’ll check the legs on all the remaining customs just to make sure and I’ll go ahead and check u62. What would I be reading it as?
 
hrvat9 said:
If I cycle the pcb , the backround will also go blue , or a purplish colour. Could I send you my original rom files ? I don’t know how to plug them into mame to verify if it’ll do the same thing

I’ll check the legs on all the remaining customs just to make sure and I’ll go ahead and check u62. What would I be reading it as?
Click to expand...

The bootup process initializes the subsystems, so it's normal for them to show different colors or garbage as things get setup - it's the behavior that the board exhibits when the game is running that matters for troubleshooting.

You mentioned using the ROM Ident website before, which is fine for checking your ROM dumps. "Dump and compare against MAME" is slang for calculating the CRC32 checksum of a dumped ROM and comparing it against the CRC32 checksum that MAME has for its ROM dumps on that game. That's what the ROM Ident website does for you.

For instance, for the Japanese version of DDP, here is the MAME documentation for the ROMs, the subsystem they work with, and the CRC32 values for them:
Screenshot 2024-12-06 at 10.39.47 AM.png

You'll want to read U62 as a 27C1610 EPROM and you can use the same kind of EPROM for a replacement.
 
sweet! Looks like I’m going to learn a lot here😁
As I was looking at various different ddp roms last night I noticed that the original Roms that came with the pcb were the exact same…both burned as the u27 lol the u26 didn’t have the original label on it so they must of tried to burn a rom(the wrong one) to get it going

Also noted, that no amount of touching/tapping / bending of the pcb made any difference to the solid blue screen. Must be a code thing or, maybe someone plugged this in backwards resulting in having to change out the cpu and the neighbouring rams?? Maybe something part of the video signal is toast.

This little 8 pin chip is also socketed , there’s an atmel 93c46 in there now.

I haven’t posted a pic of the pcb yet so here’s one
 

Attachments

  • image.jpg
    image.jpg
    184.1 KB · Views: 70
  • image.jpg
    image.jpg
    259.3 KB · Views: 66
Last edited:
The 8 pin Atmel chip is the EPROM - it stores high scores, game settings and bookkeeping data.

I think the solid background changing color is either a loose pin on one of the tile rendering custom chips, or a faulty tile ROM occasionally sending a different signal. Are the tile ROMs socketed on your board like the CPU ROMs were? If so, the wrong chips might be installed as you found with the CPU code ROMs.

This section of the board renders the three tile layers - focus on that. Each tile layer has its own dedicated custom graphics chip, ROM and RAM.

Check the pins on the three large custom chips for loose connections or solder bridges. Check the traces that connect each custom chip to its corresponding ROM and RAM. Dump the ROMs and use ROM Ident to check the dump against MAME. Sewing needles are common, cheap and useful for checking for loose pins on the custom chips. :D

image.jpg
 
Yep, I think swapping out the U62 part is a logical next step. Install a socket so that you can easily swap the original ROM back in if it ends up not being the culprit.
 
Hmm…so still a solid blue screen after swapping out all three background tile EPROMs. That’s unfortunate.

I recommend a logic probe for the next step. Probe the CE pin on each EPROM and make sure it’s being enabled. Also check the Address and Data lines for activity.

This is an inexpensive logic probe that works well:
https://www.amazon.com/gp/aw/d/B000Z9HAP4

I made a tutorial video a while back on how to probe EPROMs with it:
View: https://youtu.be/2PAtTIAijeA?si=t6khC-m9_sYETySI
 
ShootTheCore said:
Hmm…so still a solid blue screen after swapping out all three background tile EPROMs. That’s unfortunate.

I recommend a logic probe for the next step. Probe the CE pin on each EPROM and make sure it’s being enabled. Also check the Address and Data lines for activity.

This is an inexpensive logic probe that works well:
https://www.amazon.com/gp/aw/d/B000Z9HAP4

I made a tutorial video a while back on how to probe EPROMs with it:
View: https://youtu.be/2PAtTIAijeA?si=t6khC-m9_sYETySI
Click to expand...
I watched your video a while ago when i was trying to fix some toaplan games haha. I still haven’t changed out the mask roms, in the video I just had them piggybacked
 
You must log in or register to reply here.
Back
Top