Porchy

Commodore 128 repair log #3

Feb 252012

Motherboard clearly had a dodgy ON/OFF switch.
Removed it and replaced it with one from a C64.

On power up I had a blank screen.
Did a few quick checks with the scope and all data/address lines were pulsing properly.
Checked the voltages with a multimeter, the 5v was present but the 9VAC was not. Traced this right the way back to the switch I had fitted.
When I soldered the new switch in, one of the legs musnt have made a connection as they were a little shorter than the original. I resoldered the legs on top of the motherboard as well as the underside and it now boots up.

One of the CIA chips was missing, fitted a new one and C64 mode now works too.

Namco PAL added

PAL Updates Comments Off

Feb 212012

I was contacted a few weeks ago with regards to dumping a PAL from a Namco PCB. The PAL is labelled SYS2V-2.
The chip arrived yesterday from Italy and it turned out to be the most difficult PAL16L8 to dump yet.
The output from the ABI was fairly unusable as it produced FAR too many product terms for some of the pins and would not compile.
Most of the pins were fairly easy to figure out from the listing but pin 12 was a little bit crazy. After a night with the logic analyser hooked up to it I had something that was almost the same in my simulation as what the real chip did. There was one state that did not match up but I emailed the .JED files anyway to see if I was anywhere near. Well so far so good as 2 of the games it was tested on seem to work now.
Although I cant test this myself Im hopeful its OK and its on my download list now.

Jumping to Rainbow Islands conversion part 4

General 3 Responses »

Feb 192012

Well today I finally finished the conversion.
Ive been doing the title screen conversion over a few days as its a very boring task

As you can see, the palette isn’t correct when originally copying the image over so this has to be changed manually after its all complete.

Once complete though, its identical to the original

All the graphics have been changed to original RI ones and plays pretty much the same.
There are still a few differences:
1. Some of the DIP switches do nothing.
2. Every now and then the sprites when a monster is killed are messed up. Cant locate the code where its going wrong.
3. Secret rooms do not work.

I can honestly say all of the images were taken from my conversion in MAME and not from the actual Rainbow Islands ROMs.
I haven’t actually tested it on the real hardware yet so it may not work the same as it does in MAME though. Fingers crossed it does.

Jumping to Rainbow Islands conversion part 3

General Comments Off

Feb 162012

Today I finished off the main character sprite. After that I started work on restoring all the title screen text.
Getting the standard copyright info back was a simple task of replacing the “1989” text in the ROM file with the text from the real Rainbow Islands ROM.

Ignore the title screen image, I made a start on changing the graphics just to see what the colours would be like.
So the text is back but there is also a red Taito logo missing. After much searching it turned out that the logo is actually being drawn but its palette is set to black so is not shown. This explain why I saw it on my real board when fault finding a colour issue.

Following the same routine I used for changing the character palette I found the value at address $229E8 and changed it from 00 to 3E which after the bitshift routine, sets the palette to 000F (Red)

And with that done I think all that is left to do is finish off replacing the graphics tiles for the title screen. This may take a while and will probably end up adding a little something to it just to set it apart from a genuine board.

I am aware that on this bootleg the secret rooms do not work. This is because the C chip is not present on the board and there is little I can do about that. Overall its been a fun little project.

CONTINUE TO PART 4

2364 to 27128 PCB adapter boards have arrived

General Comments Off

Feb 162012

A little while ago I sent my adapter designs off to get fabricated and today they arrived.
I ordered 5 of them as they were nice and cheap but as luck would have it 10 arrived, im not complaining and now I can properly install JiffyDOS in all my Commodore machines

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