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MVS 2 Slot Repair Help

r67055 said:
OHHH I forgot that UNIBIOS 4.0...
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That thing does some strange shit... I had to downgrade a customer to 3.3 on their 4 slot. It was doing strange things with Samurai Shodown (the first edition) where the game would play but had no sound. Swap in 3.3 and had sound.
 
r67055 said:
I just replaced the NEO-257. (L4) and It works
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You're welcome!

The NEO-257 is a bunch of 74LS257 2-to-1 data switches in a surface mount package. They are fed a signal on a pin to choose which cartridge slot video data to send to the ZMC2.
 
I warmed up.....
little deacidification.
if this ever works.....?...😀
 

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a quick question..... i found a faulty 74AS245 ic
can I put a 74LS245 instead?
MV4FT
 

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No. Maybe a 74F, but not a 74LS. The fanout capability of AS is much much higher than LS.
 
channelmaniac said:
No. Maybe a 74F, but not a 74LS. The fanout capability of AS is much much higher than LS.
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unfortunately I found this 74LS245. I installed this instead until I get a 74AS245. is this causing this error?
 

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r67055 said:
I warmed up.....
little deacidification.
if this ever works.....?...😀
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I don't think I need this for life. which is bram (Back up Ram)? 1-2-3-4? if bram=back up rom, is ram 1 or 2 or 3 or 4 at fault? or do you have to look for the error in the lines?
 

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its usually going to be something wrong with the OE signal going to the ram chip
 
r67055 said:
I don't think I need this for life. which is bram (Back up Ram)? 1-2-3-4? if bram=back up rom, is ram 1 or 2 or 3 or 4 at fault? or do you have to look for the error in the lines?
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Backup RAM is the RAM that has pin 28 NOT connected to the +5 JAMMA Edge Connector for power. There are 2. One is upper that is connected to the upper 8 data bits and the other is lower and is connected to the lower 8 data bits of the CPU. Check continuity to ID which RAMs are which. :)
 
channelmaniac said:
Backup RAM is the RAM that has pin 28 NOT connected to the +5 JAMMA Edge Connector for power. There are 2. One is upper that is connected to the upper 8 data bits and the other is lower and is connected to the lower 8 data bits of the CPU. Check continuity to ID which RAMs are which. :)
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thank you for the guide.

I check the lines
 
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