I’ve had this PCB on a pile for nearly two years, decided it was time to look at it.

Symptoms

There is no Green on the graphics, Red and Blue are fine, but colours look washed out because of this.

Started at the edge connector, and using the probe checked the Green pin and it was stuck low, the Red and Blue were pulsing nicely as I would expect.

Traced the Green video path all the way to the second layer which is the main CPU board and smaller. Found a Transistor (TRM3) which had been crushed and legs were shorting, effectively grounding the Green video.

Straightened it out and all good now, full colour is back.

Thing to note is that these Transistor protrude quite a bit, and since these Namco System 1 boards do not have legs, the board tends to sit resting on these Transistors. One to watch out for if you lose a colour on a Namco System 1 board.

Had a look at a Taito New Zealand Story which was not booting for someone.

Symptoms

The PCB would not boot, would be greeted with a BANK RAM ERROR message, then the PCB would attempt to reboot every 5 seconds.

Had a look at this tiny PCB, and noticed it only housed two large RAMs, a 6264 and a 6256 (HM65256B). One must be for graphics and the other program code, I didn’t bother with schemes to check which was which.

The BANK RAM ERROR message meant either a RAM buffer had failed, or one of the RAMs, given that the PCB used a single large RAM instead of several smaller ones, so the message could apply to a single RAM in this case.

Checked the buffers, they checked out good. Then checked the 6256 RAM at location U31 first, good guess as I found one of the data lines was floating using a logic probe.

Desoldered it, socketed the PCB and inserted a new RAM.

All working 100% now.

Another on my pile that has been wanting attention for a while. It is an original PCB and is the YM2203 version unfortunately, much prefer the YM3526 version with superior soundtrack.

Which version you have is easily identified by a daughterboard (YM2203) on the underside of the PCB.

Symptoms

PCB will not run at all, all I get on the screen is static garbage which is always the same whenever I try to boot.

I started by looking at the clock circuit, I did this by checking the 68000 CPU’s Clock (CLK) pin which was pulsing as I expected, so the clock circuit must be good. The next thing to check was the RESET pin on the CPU which should have been HI, but it was LO and stayed LO, which mean’t no watchdog system was barking. Pin should have flipped to LO for a split second on boot and stayed on HI for an enabled CPU.

I probed further and checked the HALT pin on the CPU, which was LO, this told me there is a Bus error somewhere and the CPU has put its handbrake on.

Next thing to do was verify the CPU program ROMS (1, 2, 3, 4, 5, 6, 7 & 8 ROMs) were good, as there is no point checking the PCB any further if it has nothing worth running. They all checked out good.

Next I checked the CPU buffers (74LS244), which were inactive as I expected but checked out good.

Ok I thought, must be the CPU RAM (6116) which is bad at locations 10b and 10d, I checked them but they were inactive as I expected, so desoldered them to test them. They both checked out good.

Hmm….at this point I had checked all components on the PCB which would stop the CPU running. I probed further and started to check the Caps. I found a Cap which when I checked both poles with my logic probe, it showed LO for both poles instead of LO (-) and HI(+) which I expected. This can only mean the Cap is shorted. I checked again with a Multimeter which confirmed this.

Off it came;

I soldered in a new Cap and the game came right up!

However, I was not finished yet! Time to convert this YM2203 PCB to a YM3626 version.

First, I removed the daughterboard, you can see the large YM2203 IC on the daughterboard with the Nichibutsu markings on it. The other large Nichibutsu on the PCB is the Z80A for the games sound and soundtrack. Was this an attempt by Nichibutsu to disguise these non-custom components?

Then we need to reburn ROMs 11(15b) & 12(17b) with the sound code from the YM3526 version of the game from MAME. Also, we need to introduce ROM 13(18b).

Next, seat the YM3526 IC where the daughterboard once was;

Job done!