Another great horizontal shooter from IREM.
Very low volume was the first issue. Checked the volume pot as it had been changed. Was the correct value. Replaced the 1000uf capacitor that was visibly bulging and the sound came back very loud!
When it is first powered up all the ROMs and RAM 7 show as bad, but powering the game off and on again reports RAM OK ROM OK.
Left for a few minutes it doesn’t again.
Having already replaced the capacitor which was bulging, the rest of the capacitors were suspect.
M72 games have a reset chip at ic7, with two timing capacitors. Shorting out both when the board was powered off produced the same error message every time. Replaced both capacitors at C8 and C10 got the board reliably booting.
This little pcb was created by Radich Electronics back in the day to convert a bootleg defender boardset into a Robotron boardset.
But where is the Special chip 1 pair you say? All the TTL logic above the roms implement the blitter chips. In a attempt to prevent copying they have sanded off all the identifying labels.. even underneath the chips!
Fortunately nowadays we have chip testers that can identify any TTL chips, so I am currently labourously desoldering and identifying each chip. Next step is to scan the pcb and make a net list to create a schematic. There are tools out here to assist with reverse engineering but they are all expensive, or require paying someone else to do the work.
The natural progression for Sega after the popular system 16 and system 18 games, was system 24. Higher resolution graphics meant using a medium res display and needed more memory to store the graphics data. Sega’s solution was to use a cheap medium instead of expensive eproms. Over 8 megabits of data…. Floppy disks! How can it fail. But wait, floppy disks can be easily copied, so Sega continued the usage of their FD1094 security processor.
Move forward 20 years and arcade collectors have a major pain. FD1094 batteries failing and disks either getting lost, or damaged from overuse.
A cheap repair/fix solution is needed.
Putting together a System 24 USB adapter, modified System 24 bios and a disk server program running on my PC and voilà, nice fresh disk images can be written using the System 24 hardware itself.
Modified Bonanza Bros disk running on a Dynamic Country Club rom board
My System 24 Scramble Spirits cabinet buried under stuff
At the request of a friend I was asked to fix the inverted screen issue with Athena.
An hour or so at the hands of the MAME debugger and a couple of false attempts the resulting patch is a simple two byte change to the rom.
In rom up02_p4.rom change these bytes. (actually, the patch swaps them around)
$029e to $48
$02a4 to $3e
Burn a new 27c128 rom and its done. Since we are swapping two bytes, the checksum doesn’t change.
Edit: Tested on a real pcb. Works perfectly as expected 🙂