[Alcahest]

Hey all,
I tried all the English patches from the MD translation section and the following roms end up with a wrong checksum:

- Dahna - Megami Tanjou (Japan) v1.0 by cccmar

- Dynamite Headdy (Japan) v070428 by M.I.J.E.T.

- Fushigi no Umi no Nadia (Japan) v1.1 by KingMikeTranslations

- Panorama Cotton (Japan) v1.0 by Malias

- Psy-O-Blade (Japan) v1.1 by EienNiHen

- Sonic Eraser (Japan) (SegaNet) v1.0 by D

- Star Cruiser (Japan) v0.991 by NebulousTranslations

I tried contacting the patch creators but most have no contact info (expect cccmar, M.I.J.E.T. and Malias to whom I fired a mail).
How would I go about contacting the other authors to let them know about the issue?

[EvilJagaGenius]

Probably the better option is to use a tool to fix the checksum yourself, like this: http://www.romhacking.net/utilities/342/
Some emulators have options to auto-fix the checksum too, if you're using one.

[Alcahest]

Thanks, yes I found this tool, along with this one https://www.romhacking.net/utilities/1344/
and I certainly can fix them on my end but I thought authors would be interested too (in order to release fixed patches, etc..).

For instance all of M.I.J.E.T. MD patches generate roms with correct checksums except Dynamite Headdy, which I found odd.

[KingMike]

I know there are some Genesis games that, even unmodded, have a bad checksum.

Not sure if anyone has bothered to make a list.
Retrode has noted Blaster Master 2 as one example.
I can't recall if Zero Wing has a "bad" checksum (as I know both regions have the effective ROM size wrong in the header). (that is, if the checksum matches either the wrong 512KB size or correct 1MB size.)
MegaPanel is another I know, as I have personally dumped my cart a few times to check, even tried overdumping it with the same result.

[FlashPV]

By the way, I couldn't get Dynamite Headdy working. I'm using Kega is it an emulator problem?

[Alcahest]

@KingMike, interesting, and these still run on original hardware of course ?

By the way, I couldn't get Dynamite Headdy working. I'm using Kega is it an emulator problem?

Possibly, make sure the source rom (JPN) has MD5:
cdb36911439289d3453060f58682057c

And the generated rom should be:
d43cd7d31616d2992e3b1ac389ef4eb1

[TheGershon]

I have roms with those checksums too and fixing the header actually makes it NOT work. It plays fine without doing so on Genesis Plus GX.

[KingMike]

@KingMike, interesting, and these still run on original hardware of course ?

I don't THINK the original console TMSS verifies the checksum, just checks for things like the "SEGA" text?

(different than some developers, such as EA, who wrote self-verification routines into the games)

[Alcahest]

I don't THINK the original console TMSS verifies the checksum, just checks for things like the "SEGA" text?

(different than some developers, such as EA, who wrote self-verification routines into the games)

Yeah TMSS mustn't be verifying the checksum, most likely. Apparently only certain roms perform a self-check, not the whole library.

Btw Malias released a fix patch for Panorama Cotton's checksum
November 07, 2019, 05:55:44 pm - (Auto Merged - Double Posts are not allowed before 7 days.)For M.I.J.E.T.'s Dynamite Headdy, turns out the bad checksum is intentional.

This game uses a non-standard method to calculate the checksum.
If the checksum really is bad, you'll get the "red screen of death".