Truxton/Tatsujin help

[xodaraP]

Hi guys,

I have a Truxton board that isn't working - I've checked all the ROMs which are present and correct, the customs are all making good contact (that wasn't a quick job with a multimeter) and both the Z80 and 68k appear to be fine (I have replaced the Z80 as I believe it wasn't happy). I know that the 68k won't start unless the Z80 is running correctly, but I'm not sure what's holding up the Z80.

- Z80 is stuck on reset, 68k is running (reset line is high)
- Both CPUs have clock
- ROMs have tested ok
- Main program RAMs (6264) have been pulled and tested ok
- Sound RAM (6116) pulled and tested ok
- Sound ROM replaced
- Yamaha YM3812 pulled and replaced (connected to Z80 reset line)

This is what I get when I plug it into the Astro:

And I probed the sync line with the scope to see what I get there:

 

[caius]

Those wavy lines mean the system is not being correctly initialized, all Toaplan games on same hardware behave in this way.As you said (and I guess you read it on JAMMArcade repair logs, we spread our knowledge all around...) probably the sound system is not running and this prevent the whole system to boot.Now it's up to you to figure out why

 

[xodaraP]

I did indeed get the information from your repair logs

It narrows it down, but the sound system goes literally all over the board since the I/O is part of that system :/

 

[xodaraP]

So fortunately enough I have 2 of these boards here, neither is working. Ironically board number 2 is in a much better overall condition, but the custom silkscreened SCU on the board is completely rusted on one side and sadly can't be fixed, the pads are completely trashed. I guess the option is there to rebuild the whole side by connecting wires to the pins, but not much else can be done. At least it means I can check the clock signals etc. and make sure they are correct.

 

[xodaraP]

I have looked through the MAME driver and the Z80 is responsible for checking these before the 68k is fired up (not necessarily in this order exactly)

- All controller inputs checked

- Coin counters, DIP switch banks, tilt switch, territory jumpers and all other inputs checked and settings loaded into shared RAM between the 2 CPUs

- YM3812 activated

- VBLANK signal activated

There are things I can't work out

- The VBLANK signal is generated from a custom according to the MAME driver, but I don't know which one (I believe it's the SCU)

- The line that has a note on it saying coin counter/lockout writes to "toaplan_coin_w" and I can't work out what this actually does. I see for another game this same thing is done via an LS259 - is it the same thing here and they have just given it a function name? I can't find a 259 on this board

- The YM3812 appears to be functioning fine, but I also don't know what I'm looking for

- It makes no sense to me that the game completely fails to boot if the YM3812 or something in the input section isn't working - as per this repair log:

http://www.jammarcade.net/rally-bike-repair-log/

Where the game still started but there were issues with controls and sound.