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View Full Version : bombjack garbled background ???



Davefjedi
29th November 2005, 10:15 AM
hi all just wondering if someone can tell me wether the backgrounds on a bombjack pcb are on a singlr chip or multiple chips the game is playable with the only issue being the background being blocky it is there but in blocks the rest of the game is ok ie the first level the pyrimid and sphinx head are just dark blocks
dave :cry

MadMikeAU
29th November 2005, 11:02 AM
The backgrounds in Bombjack are 16x16 tiles. The definitions of which are on a eprom. The layouts on another. Sounds like the definition eprom is needing attention.

Prof
29th November 2005, 08:48 PM
Its a single 2732 (Roms 6 Location 8L IIRC). I have seen the (shitty) roms they used here break legs off when removed. If it's not that rom, it would most likely be the ram, then the decoder circutry.

MadMikeAU
29th November 2005, 11:43 PM
Looking at the romset, you can see that rom 2 @ 4P contains the background layouts as 16x16 tile maps. By what you are describing, this is good.

The definitions for these tiles are apparently roms 6,7 and 8 @ 8L, 8N, 8R respectivly.

FYI:
* Bombjack does a big test at boot, including the ram and the code roms (but not the grafix).
* To change the background, the cpu writes a 1 byte code which gets latched. It is an offset for ROM2. This looks to be working.

I'd still say have a look at ROMS6,7,8...but for all of them to be playing up...maybe the decoder circuit has a fault. Test the voltage and enables for these. Check the output starting at the data lines. Hope this helps.