Heyas, been away a while but slight return to arcade stuff so decide to do a writeup.
Got hold of a CPS-1 Final Fight as a trade. I already have a worker so was quickly able to determine the fault lay with the A board.
Initially thought it was dead but it was actually playing blind.
Did a google search to see where the state of play was with CPS1 repairs and came across this page;
pcbjunkie.net
A nice if basic writeup of some faults and where to find them. Looking at the motherboard I saw the frame ram chips were Sony CXK5814, which from memory (oops bad pun) fail a lot, so piggybacked one with an equivalent TMM2018 and got this;
Progress, but no objects or backgrounds, just one layer of graphics, which I assumed was the 'character' layer.
Replacing all 4 frame buffer rams got me this;
But still no objects. Could see some faint discoloured pixels in the centre and bottom of the screen. At this point I suspected video ram or the dreaded CPS-A-01 failure, but as many will know the motherboard is underneath the romboard its a right pain to work on.
Bit more googling around I came across this;
www.arcaniac.com
Bit steep but what the hell, I bought it. Came fairly quickly from Canada and couldn't wait to play with my newtoy diagnostic hardware.
Plugged it all in and suspected the graphics DRAM to start with so was using a logic probe to see if any data/address lines were dead (they weren't). Thinking of dragging the scope out when I noticed some of the rams were getting really hot. Way beyond normal, and only some of them. Checked the schematics to determine if possibly a tied control line could be causing the problem but they were in different banks, and the control lines were pulsing.
At this point I made an educated guess it was the DRAM. Couldnt find any TMS4461 at a reasonable price so bought the alternative HM53461ZP from Aliexpress. They're a different form factor but the motherboard has provision for either.
When they arrived I snipped out the 6 hot rams and started replacing them. I tested after the first one was installed (I chopped up some turned pin sockets as I want going to solder the RAM in directly) and got objects appearing, partial and flickering, but there. I carried on (replacing 2 more RAMs in the same bank as the hot ones that seemed to store the object sprites) and eventually got a fairly complete picture, but with a central band of iffy pixels, demonstrated here in 1941 in test mode;
Made an educated guess it was further faulty RAM (IE dead cells) and decided to replace the remaining 4 original DRAM chips... at this stage why not? This fixed the problem.
a total of 16 bad RAM chips and could've just bought another A board for the money and time I've spent but that's not the point, is it? Was just relieved it wasn't the custom. 😅
New DRAM (top right)
Some of the dead;
Got hold of a CPS-1 Final Fight as a trade. I already have a worker so was quickly able to determine the fault lay with the A board.
Initially thought it was dead but it was actually playing blind.
Did a google search to see where the state of play was with CPS1 repairs and came across this page;
Capcom CPS (CPS-1) Repair Guide – pcbjunkie.net
pcbjunkie.net
A nice if basic writeup of some faults and where to find them. Looking at the motherboard I saw the frame ram chips were Sony CXK5814, which from memory (oops bad pun) fail a lot, so piggybacked one with an equivalent TMM2018 and got this;
Progress, but no objects or backgrounds, just one layer of graphics, which I assumed was the 'character' layer.
Replacing all 4 frame buffer rams got me this;
But still no objects. Could see some faint discoloured pixels in the centre and bottom of the screen. At this point I suspected video ram or the dreaded CPS-A-01 failure, but as many will know the motherboard is underneath the romboard its a right pain to work on.
Bit more googling around I came across this;
Capcom CPS1 A Board Diagnostics / Repair Tool
This tool allows you to mount a CPS1 A board (motherboard) above the B and C boards. Giving you easy access to all the IC pins and making it easier to probe and troubleshoot issues with the A board. Without resorting to blind or educated guesses as to what might be wrong. FEATURES /...
www.arcaniac.com
Bit steep but what the hell, I bought it. Came fairly quickly from Canada and couldn't wait to play with my new
Plugged it all in and suspected the graphics DRAM to start with so was using a logic probe to see if any data/address lines were dead (they weren't). Thinking of dragging the scope out when I noticed some of the rams were getting really hot. Way beyond normal, and only some of them. Checked the schematics to determine if possibly a tied control line could be causing the problem but they were in different banks, and the control lines were pulsing.
At this point I made an educated guess it was the DRAM. Couldnt find any TMS4461 at a reasonable price so bought the alternative HM53461ZP from Aliexpress. They're a different form factor but the motherboard has provision for either.
When they arrived I snipped out the 6 hot rams and started replacing them. I tested after the first one was installed (I chopped up some turned pin sockets as I want going to solder the RAM in directly) and got objects appearing, partial and flickering, but there. I carried on (replacing 2 more RAMs in the same bank as the hot ones that seemed to store the object sprites) and eventually got a fairly complete picture, but with a central band of iffy pixels, demonstrated here in 1941 in test mode;
Made an educated guess it was further faulty RAM (IE dead cells) and decided to replace the remaining 4 original DRAM chips... at this stage why not? This fixed the problem.
a total of 16 bad RAM chips and could've just bought another A board for the money and time I've spent but that's not the point, is it? Was just relieved it wasn't the custom. 😅
New DRAM (top right)
Some of the dead;
