The 7th Guest is a great game for Phillips CD-i. Unfortunately there is an annoying bug that crashes the game when trying to solve the cake puzzle:
It was widely believed that the bug only appears on the newer players and that the only solution was to buy V2 of the game (e.g. here, here and here). Well, that’s only partially true. The bug in the V1 game is triggered by the IMPEG 6.x digital video cartridges.
Let’s have a look at the game, these are the German versions. Everything is identical except disc 1 and the VCD jewel case. Some say that the jewel case is not a clear indicator of the version though.
On a closer look at the inner ring of disc 1 you can see the version numbers (V104 and V203):
With IsoBuster we can view the content of the disc and note that one file was changed in V2: cdi_t7g
I ripped the discs with CDRWIN and compared them to the TOSEC rip, the CRC32 of V1 is 72D1B393. A known rip, also used for the CHD in MAME/MESS. The checksum of V2 is 42063086, that rip is not known. Checksums of the file cdi_t7g: V1 8715F32A (German and English EU versions) and V2 7B263600.
For a quick fix you can download this archive, it contains XDelta 3 patches V1 to V2 (German disc 1 and cdi_t7g). Probably you can fix other language versions with this file too. I haven’t found a way to inject single files into CD-i disc images yet and a hex editor won’t help as the size differs.
Now, what causes the bug? Here are some 22ER9956 DVCs:
All revisions 22ER9956/20 to 22ER9956/39 contain a 5.x ROM and a VMPEG chipset. Revisions /40 onwards contain a 6.x ROM and an IMPEG chipset (integrated audio/video in one IC). For a complete overview look here.
Top row: VMPEG cartridges – 22ER9956/20 and 22ER9956/37, no differences
Bottom row: 22ER9956/40 IMPEG cartridges – November 1995, October 1997 and the version without case for newer players. No differences, except the 1995 version has the EEPROM in a socket.
If you have a CD-i player with pre-installed DVC / without DVC maintenance door then it has most likely an IMPEG DVC and is incompatible with V1 of The 7th Guest.
Before trying to hunt down V2 of the game in the language of your choice you should consider to replace the DVC with an older VMPEG revision. It won’t fit until you move the plastic holder out of the way – watch the power and CD cables! You could remove the metal case of the DVC and secure it into the plastic holder as well.
And now enjoy the game. When you see the cursor then the bug was avoided successfully: