Taito Grand Champion Repair Log

[Kaizen088]

I decided to see if I can get my Taito Grand Champion PCB working today.



The pinout wasn't available so I worked it out from the schematics and uploaded it to KLOV.



Manual here:

https://drive.google.com/open?id=0B0kAwpS2NEYzaE51SkpqX3FEb00

I made up a Jamma adapter so I could work on it on the test bench.

I have two boardsets, one was the original from the cab and looks like someone has poured a can of Coke over it.

The other is one I bought untested from The Arcade Boneyard ages ago and when I plugged it in there was nothing on screen.

The boards and cab resto were put on hold for the last 12 months or so.

So my test procedure when there is no activity is to start at the clock and move out from there.

After a bit of probing around I could see that the 74LS161 at 4L was dead on all outputs.

It was removed and socketed and new chip installed.

I now had life coming from pins 11,12,13,14.

Still no image on screen.

Further probing down the line and I found weak signals coming from the 74LS161 at 5L.

It too was socketed and replaced and there was a flash of image when the board was powered up.

The out put at pin8 on the 74LS74 at 7K looked weak as well so it was socketed and replaced.





When the board was powered back up again I got this image on screen but it kept resetting over and over.



I started thinking, okay Power On Reset...

Went back to the schematic and found pin10 on the 74LS00 at 15E was pulsing.



When I tied pin6 of the 74LS393 at 16F low, the game booted up and played as normal.

https://www.youtube.com/watch?v=FFGNqjoKWJk





That's about as far as I got today.

I'll plug it in the cab tomorrow and see how it goes.

Kaizen0882017-04-01 00:48:49

 

[Kaizen088]

I spent half the day on the steering wheel assembly.

Cleaned the old gummed up grease out of the the bearings and gave them a light coating of lithium grease.I would have normally used graphite dust but I was too lazy to go looking for the bottle.

I gave the steering wheel and the brackets a quick coat of silver hammertone to help slow down the rusting process.







There were two extremely crusty looking caps on the opto board.



I didn't have axial caps so I substituted two that I had pulled from an old TV chassis.



One of the indicator LEDs on the PCB pulses very dimly as you rotate the wheel, the other seems to do nothing.

I'll put the logic probe across it later and see what's going on, the PCB has +5v supply going to it (measured where the caps were replaced).

 

[smarty]

Nice work, this is a great game.

 

[Kaizen088]

I've been working on this on and off for a few days now.

I went through the steering opto board and removed the three TTL IC's, installed sockets and replaced with new chips.

I replaced the dim LED as well.

I took some photos when the IC's were removed so I can see where the tracks are going to as I don't have a schematic for the board.



I now get a pulse from the two pins on the opto edge connector.

They are constant low and pulse high only when you turn the wheel.

Both LEDS are indicating the opto's are outputting.

[tube]2IUTKOyj5sU[/tube]

https://www.youtube.com/watch?v=2IUTKOyj5sU

I plugged everything back into the cab and there was still no steering input to the PCB.

Both lines were tied low.

I can only get credits through the service switch.

I remembered seeing jumpers on the board in the schematic and set about discovering what they do and how to change them correctly.

On closer inspection the two boards have different jumper settings.

I photographed both of them before making any changes.

Asia Pacific PCB on top, US PCB on the bottom:



The board I got working was purchased from the US.

I think they were set up differently there.

I pulled all of the ROMs from my original board and swapped them over to the working board one at a tie testing for errors between each chip.

GM01 turned out to be faulty but all others seemed okay.

My original board had GG01-GG04 chips at row H where the US PCB has GM03-GM06 at row H.

There are also some jumpers added to the bottom of my original PCB that I will get around to tracing back.

After putting on my +2 glasses and having a look at the sockets I found the CPU socket had lots of corrosion/oxidation on the pins.



All sockets will be removed and replaced, I'd like to get my original board up and running.

The boards seemed to be covered in a wax like substance that Contact Cleaner wouldn't even touch, I thought if it is wax then heat will wash it straight off.

I threw the boards in the dishwasher for two cycles and they came out much cleaner.



Once the sockets have been replaced I'll get back to repairing the original PCB.

Now back onto the working PCB.

I traced back the jumper settings for the coin input (JP(D) and JP(K)and set them for both options but still no coin input.

I traced the signal back to the 74LS253 at 13K on the top PCB.

I can't see the signal past there so I'm kinda stuck without an oscilloscope, there is activity on the outputs but that should be there even without the coin switch closed.

I ordered 10 74LS253 chips which should arrive in a day or so.

I'll replace 13K and move on from there.



I also bought this off ebay for the cab.



The steering Jumpers are JP(E) and JP(F), I'll also get around to tracing them back to see where the signal is going.

Kaizen0882017-04-13 13:17:26

 

[Kaizen088]

This arrived a few days ago, it's the Japanese version of the manual and has more detailed schematics of all board revisions and includes the steering as well.
The schematics fold out to and are much more clearer to read.







I got to work on the other boardset and confirmed all ROMs.

There were two faulty ones so replacements were fitted.

I'll try to spend a bit of time on Tuesday (public holiday) to get this sorted.