moflih.morad
Student
I bought this Namco System 11 board for 10$ as a scrap board
the SONY CPU/GPU board was missing almost all of its capacitors, one of the caps took away with it a ground trace, several pins of the Sony CPU CXD8530 were broken
doing some research i suddenly realized that this is a Tekken 2 board, so i got excited about the idea of repairing this board. so i got down to work.
the first thing that I've done is of course test the motherboard, between the missing cpu pins and caps it was sure that the test result will be a total BLACK OUT no sound no image beside a faint static
so next i repaired the missing CPU pins.
And put all the missing caps
now tested the thing again ..... nothing total BLACK OUT
my next step was to inspect the Namco board since i didnt know where to start, while inspecting i smelled the fishy signature scent of bad 90's caps; followed the smell led me to
the sound amps caps, really stinky ....
Replaced the caps and tested...
Now i still have nothing but something changed, i can control the volume knob and get louder static (isn't this great
)After further inspection of the Namco board focusing on traces i found something....
A nice sword cut of one of the traces which is a trace for Address line of one of the latches related to sound logic.
After repairing this cut guess what.....
the board woke up and said the famous
"GOOD MORNING" but still no image and no activity. beside some rotten vias here and there that i repaired i could find anything else..
While inspecting the Playstation documentation i noticed that the CPU has a BIOS chip select pin, which is normally one of the first things any CPU
would use upon starting is to check for a boot code. so i decided this is where i should start.
With the help of my modest logic analyser i probed th CS2 (bios) and other signals on the sony board; below is the result:
here we can see signals (Clock, READ, BIOS)
the clock is the frequency used by the CPU for its operation and it looks fine and healthy (33Mhz)
next we see the BIOS signal going low (means it activates since its an active low signal) and while its active the CPU tries to READ data multiple times.
these are normal operations until you realize that these events keeps repeating, meaning that the cpu is looping without any result to see on the screen !!
now i know that the bios program cannot be loaded by the CPU on start up.
time to go back to the NAMCO main board again, looking through the schematics and following the CS2 bios and read signals, i found that they reache to IC(2B) which is a "line driver" probed the signal in and out of this IC and it goes through fine.
next the two signals forks to IC(2R) which is a PLD, and IC 2L,2J which are flash roms, so i deduced that flash roms 2J,2L holds the bios code the sony CPU is looking for;
so i had to check if the data in these flash roms is correct, i took it out and up to my programmer, i compared both 2J and 2L to the previously dumped roms from internet and none matched !!
so i checked these two roms in mame and to my surprise the version i had was never dumped before, so i went ahead and sent a message the mame community and they took care of adding it to mame.
now back to the repair; with bios flash roms and their content both OK (bios code is there, and signals bios and read are both received). so whats wrong! why data isnt going out of the Flash roms through the data bus and up to the Sony CPU !!
Going back to where BIOS(BBOOT) and READ(RDE) signals forks and go in IC 2R, the signals effectively reach this IC but... from the other side i cant really know what the output signals are ought to be since its
a programmable logic array and i could not asses if the signals generated by this PLD is correct or no. so this was a dead end for me. i had to jump back to the Sony CPU.
this time i probed the data lines of the Sony CPU to see if any thing is comming out of the Flash roms. the probing showed flat data lines (Sony CPU side and Flash roms side), no activity.
so there was something wrong with the Data bus lines this bus (as you can see in orange) is shared betweent multiple ICs, but the only way the Sony Board accesses this bus is through
ICs 6B and 7B which are tranceivers that controls access to the Data bus lines between Sony Board and Namco Board.
according to the tranceivers data sheet there is a signal (OE) that sould be driven low in order for this tranceivers to grant access to data bus lines. this signals remains always high no matter what.
tracing the signal back i found that it leads to an output of the IC 2R the PLD we've seen previously this output is labeled DATAG on the original namco data sheet.
i started to suspect that the PLD itself might be the culprit, as a quick test i've manually driven the DATAG signal low with ground through a resistor.....
guess what !! the board starts and shows the settings screen.
so indeed the PLD was at fault, took out the faulty PAL, ordered a new GAL ic(since my programmer cannot write to a PAL) and downloaded the JEDEC file to program this new GAL.
installed the new GAL and the PCB started up Good morning, Color Bars, and.................................
KEYCUS error !! ooooops
so i guess after all this hard work it all came to a dead end but at least we have some progress..... well maybe some super hero will come up with a Keycus bypass rom one day.....
until then i have to wait patiently to see this through.
thank you all for reading this post, any suggestion would be welcomed
see you soon...
