Capcom Buster Bros / Pang arcade pcb repair #2
A dirty beat up board showing no signs of life (not only no video sync but no activity on any TTL anywhere on the board). Previous owner had installed a ‘desuicide’ patch (see other Pang repair) but there was obviously another problem if the CPU is not getting a clock signal.
The crystal oscillator on the board was rusty and had obviously taken some physical damage but it still worked so the next step is to trace where the output signal goes. And it went pretty much nowhere – terminating at the empty FB42 pad right next to it. Closer comparison to a working board showed there should have been a component there, it must have been physically broken off the board (however FB43 is intentionally empty). I wasn’t familiar with this type of component package but apparently FB is ferrite bead in this context, which is usually used as a high frequency filter. The Capcom packaging isn’t one I recognise though and it has no markings on it to indicate the frequency or impedance.
So without a replacement I just bridged it with a wire… you shouldn’t really ‘need’ a filter right after the oscillator even if this board’s designers intended it that way. So with that patched the board sprung to life with a solid green screen – so clearly the clock signal is now reaching the parts of the board it’s meant to.
Solid green screen is an indication the CPU isn’t running, perhaps because of the battery suicide. I took the CPU and de-suicide ROMs from the other working board and tried them here – board came up straight away, 100% working graphics and sound!
So by trying combinations of ROMs and CPUs from the two boards it became clear the encrypted Kabuki CPU itself had failed. That’s unfortunate but not a big deal as with the de-suicide ROMs and patch a regular Z80 can be used in it’s place.