Diagnostic Software

Ask anything your want about Mega/SegaCD programming.

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Sylver
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Posts: 1
Joined: Thu Mar 26, 2020 9:15 am

Diagnostic Software

Post by Sylver » Thu Mar 26, 2020 9:46 am

Hello guys,
I'm a software/electronic engineer with a lot of embedded development experience (real time and stuff like that), and I have a hobby : repair old game consoles ! I recently got a wonderful Sega CD-X that is faulty (like most of the consoles I get :mrgreen:). And after doing everything I could (capacitor recap, replacing the battery, reworked solder from 315-5860 and 315-5632 using flux and fresh solder, check for continuity between both boards, replaced the CD lens ...), I must admit that I'm stuck in detecting the origin of the problem.
Now the problem is quite simple : It works very well for the cartridge part, but if it boots the Sega CD part, I have the main screen with the earth and moon, the bios version written on the upper right side, and that's all, no colourful SegaCD logo in the middle, no "press start button" text, ... And nothing happens !
I've read some service manuals for MegaCD (as service manual for CD-X is not available) that the bios is performing some self tests at startup and if one fails, the bios will not start correctly ... I think that this is the issue I have.
I have an overdrive so I could run any custom application or even custom CD bios :) So I think that my only option now is to find which self test is failing ... One option would be to recompile the bios with some modifications (like some text printed after each self test to know which one is failing), or to create a self test program !
I think the second option would be the best in term of compatibility (no need to have a different program for each model of Sega CD), but I'm afraid that lot of things could not be tested if the console did not start in Sega CD mode ...
So maybe some expert here could help me to make things more clear for me about what could be tested from main 68k CPU (memory chips ?) and what could only be tested by second 68k CPU. And it is possible to make some code run on the second CPU while in Genesis mode (executing code from the cartridge).
I've read in the service manual for Mega CD that there is a test cartridge/cd available to test MegaCDs, but I could not find any rom/iso regarding this, so maybe creating one could be useful for saving some faulty Sega CDs :)
Thanks,
Sylver

KRIKzz
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Posts: 24
Joined: Wed Jul 22, 2009 11:25 am
Location: Ukraine
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Re: Diagnostic Software

Post by KRIKzz » Tue Jun 30, 2020 11:17 pm

https://github.com/krikzz/MEGA-PRO/tree ... erificator

Try this thing if you have some flashcart. It tests pretty much everything. If it not start at all then sub cpu or wram likely broken.

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