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Help with MVS 4 Slot Watchdog

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ArcadeBattler

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Hello,

I have a 4 slot mvs which is stuck in watch dog, I have tried using the diag bios on it but the board isnt able to boot into it. I also tried jumping the watch dog disable jumper.
 
Stuck? Battery damage can cause problems with the 74HC chips that are low power and gate the control lines to the Backup RAM. If those are messed up there's a chance the Diag BIOS won't boot. Try flipping all DIPs on and see if it randomly boots enough to run the Diag BIOS to report an error with the Backup RAM.

Another issue could be with the 74ALS245 chips that latch the data from the cartridge Program ROMs. They are close to the BIOS ROM. If those short the data bus will be stuck and the BIOS will never boot.
 
channelmaniac said:
Stuck? Battery damage can cause problems with the 74HC chips that are low power and gate the control lines to the Backup RAM. If those are messed up there's a chance the Diag BIOS won't boot. Try flipping all DIPs on and see if it randomly boots enough to run the Diag BIOS to report an error with the Backup RAM.

Another issue could be with the 74ALS245 chips that latch the data from the cartridge Program ROMs. They are close to the BIOS ROM. If those short the data bus will be stuck and the BIOS will never boot.
Click to expand...
I managed to get the board to boot the VEC signal line was damaged. Now I cant get carts to boot.
 
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Check the traces that run under the battery. They carry the address lines and data lines for the Program ROMs to/from the CPU.
 
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channelmaniac said:
Check the traces that run under the battery. They carry the address lines and data lines for the Program ROMs to/from the CPU.
Click to expand...
Hey I can't seem to find any more broken traces beyond the ones I repaired... The diag bios gives me CRC Error , Actual: EED53B51, Expected: 651DBEF3. I've tested the bios on another board and it works.
 
Corroded socket? Bus contention (Backup RAM will do this when their control signals aren't working properly bc of battery damage)?
 
On the diagbios page, CRC error is mentionned as bad EPROM burn, but I've read (here ?) that it can be related to 68k address / data lines being pulled up / down / jointed.
I personnaly had CRC error caused by a bad 74HC259.
 
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