This patch prevents the game AI from freezing, which happens very often if the (permanently available) takeback function is used late enough in the game of chess. The hang may happen more often on certain difficulty levels, such as "level 1 60/5".

This edition of Chessmaster, as the game of chess goes on, allocates progressively less time to "re-rolling" CPU moves which are calculated after the takeback function has been used as compared to regular CPU moves, which is dubious in and of itself. Maybe the authors wanted to meet the originally set time budget for a game even with this takeback functionality interfering. Eventually, this time slot is mistakenly calculated as negative, which is then reinterpreted as a very large number of vertical interrupts to wait for before announcing a new CPU move by the function at 0x71f4 in ROM. Unlike regular high-level play of this AI, the game apparently can't even process this large positive integer correctly and, after spending many minutes decrementing the counter containing the remaining number of vertical interrupts, enters some endless loop, and said counter is no longer decremented after that point. At the very least, the AI doesn't make a new move in this situation for no justifiable reason for more than 15 minutes, which has been confirmed with multiple emulators. This patch changes that negative quantity of vertical interrupts to a very small positive quantity, the same quantity that was used by the "level 1 60/5" AI after earlier-in-the-game "takeback events" in the moves immediately preceding the hang. This is done to intrude as little as possible into the origial code. Since only a small time slot is allotted to these CPU moves, it's better to avoid the takeback functionality altogether for serious play against the AI. If you want to disable the takeback functionality altogether to avoid worrying about accidentally pressing Button 2, don't apply this patch but instead change the byte at file address 0x2324 from 0x3f to 0x1f. It's theorized that this takeback hang only happens after roughly move 23, which might explain why this bug made it into the final game build.

To consistently trigger the hang in the unmodified copy of The Chessmaster, boot the game, immediately change the difficulty from "Newcomer 1" to  "Level 1 60/5", then press Start a few more times and select the "change sides" option. Then keep using the "Begin New Game" option until the CPU makes the first move e2-e4 (and don't forget to "change sides" at the start of each new game). Then, as Black, start inputting the following moves, but refrain from taking any move back in the process:
1. e4 c5 2. Nf3 e6 3. Nc3 Nc6 4. d4 cxd4 5. Nxd4 Be7 6. f3 Bh4+ 7. g3 Bg5 8. Bg2 Qa5 9. O-O Qc5 10. Bxg5 Qxd4+ 11. Qxd4 Nxd4 12. Rad1 Nxc2 13. Rc1 Nd4 14. Rfd1 e5 15. Be3 Ne6 16. Nd5 Nf6 17. Nxf6 gxf6 18. Bxa7 Rxa7 19. Rxc8+ Nd8 20. a4 Rxa4 21. b3 Rb4 22. Kf2 Ke7 23. Ke3 
If the CPU chooses some other line of play, use the "Begin New Game" option, change sides, and start fishing for this sequence of moves again. It never took me more than a few attempts to squeeze this line out of the CPU. Then, for the first time, take back exactly two moves 23. Ke3 and 22. ..Ke7 by pressing Button 2 twice and press Start to exit the takeback mode. Repeat your move 22. ..Ke7 by playing normally, that is outside of the takeback mode, and this should hang the AI. "Forcing" a move in the menu will not necessarily get rid of the AI hang situation on the next move. You cannot reproduce the hang with "setting up the board" option, you need all these moves to have been played, and you probably cannot reproduce the hang after inputting the password. 

Please report in the comment section at romhacking.net if the game still hangs after the use of the takeback option and the exact steps to reproduce it.

Use Lunar IPS or similar software to patch the ROM.

This version 0.1 patch was made by motke, also known as angrylion, in August 2023.