Nearly 12 months ago my Rainbow Islands went a bit crazy and kept giving me random crashes like the following

I thought I had sorted it with a simple ROM change but after a lengthy gaming session recently I discovered that this was not the case.

I couldn’t find anything wrong with this board. Sometimes I could play it for hours, sometimes it crashed at startup, sometimes it wouldn’t even start up at all.

Whilst I never gave up hope that I would find the fault I just didn’t know where to start.
My goal here is to document all the code with comments, create a decent set of schematics for the PCB and basically note any points of interest within the code and hardware.

Tonight I feel confident in saying that I have fixed my board.
While I has adding to my schematic, trying to find where a trace ultimately ended up, I found that pin 9 of IC57 (74LS138) was tied to VCC (kind of anyway, it had a resistance of 38 ohms).
The pin does in fact go to pin 19 of a 74LS244 at location IC79.

I removed the chip and it failed all tests, the connection to VCC also disappeared. I’ve replaced this chip and all seems to be well in my world once again.

For all those people that have asked me in the past “how long does a repair normally take?”. Although this kind of fault is quite rare, it has literally been 12 months of chipping away at different things. Had this been any other game then I would likely have given up on it a long time ago.

Got a Tetris that was sold as faulty.
As with pretty much any PCB I buy, a visual check was carried out and straight away I found this capacitor.

The board came with an adapter but looked a mess and the wire was far too thin on the power lines so I swapped it out.
I also found a couple of pins touching in one of the unused connectors

And finally I found the sound pot was no soldered in at all and was missing its ground pin.

I took a pot from an old scrap board and fitted it.

Now it was boot up time.

All looks ok so far, but…..

I initially thought it was a dodgy EPROM but they checked out fine. Then I realised that the EPROM at location B1 on the ROM board was missing.

I burned a new one from the Jap set and now we have this.

Everything seems to be working fine.
This board still has its battery installed in the FD1094 and surely will be coming to the end of its life by now. I don’t trust myself with a battery change but I think I have desuicided ROM’s so will just wait until it dies completely or I will sell it on as I cant imagine wanting to play this in my cab.

Where to start with this one.
My good friend brought this round a while ago with the fault of jailbars down the screen and no sound.
After messing around a bit we couldnt even get the game to boot on my setup no matter what we tried. He left it with me and ive been chipping away at it for a month or two now whenever I get time.
Ive finally got this thing up and running.
First this I found was two PLD’s, TJ-0 and TJ-1, were getting really hot.
As I have a couple of spare Caveman Ninja boards I did a swap and the game booted. Strange thing though, those PLD’s actually work in my other semi working board.
So now we have this

and no sound was present either.
Jailbars are usually a sign of a failed ROM so off the the tile ROM’s I go.
Found MASKROM MAG-02 had a few floating data pins. Replaced this for one off my scrap board and we get this

Graphics are back. Now onto the sound.
Looking first at the two OKI M6295 chips I could see neither of these were being enabled. If I pulsed the enable lines I could get various sounds to play. This tested the rest of the sound circuit so I knew it was good.
I traced the enable lines back to a 74LS138 decoder which wasn’t doing a great deal despite having what looked like good inputs. I removed this and it was indeed dead so replaced with a new one.

Still no sound though.
I could see the sound CPU and ROM were being addressed properly so next up was the RAM. On this board it was a TMM2063 chip. I could see activity on the data lines but it was struggling to drive them up to logic HIGH so removed that and that too failed a test.

I replaced it with a CXK5864 chip. Still no sound.

I started looking into how the sound section worked and found that the custom 104 protection chip is responsible for activating the sound.
I got in touch with a guy called Bryan who wrote the MAME driver and he gave me some nice information of its operation and basically pin pointed my issue to this chip.
At first I tried reflowing the pins but it made no difference so after a bit of debate with myself I took the plunge and removed the chip

I replaced it with one from my scrap board. WE HAVE SOUND!

And thats it, or so one would think. After about 2 minutes of playing this game, some of the sprites started to go a little crazy.

Going over the sprite ROM’s I found another one (MAG-06) with a floating data line. Replaced this with a spare and all is well once again.

Without a scrap board to take customs from this would have been one for the scrap pile.