Rastan repair log #1

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May 022011

Very nearly gave up with this one thinking it was a custom IC fault, glad I never.

Was sold this board as a non worker, the guy said it boots to a white screen and the CPU needed to be looked at.
He was right on both counts.


Before I did anything that CPU needed socketed. Once I had done that I fired the board up again but got the same white screen. I checked the data lines of the CPU and they were dead. I initially tried a known good 68000 CPU but this resulted in the same screen.
There are 6 ROMs next to the CPU which are the program ROMs. I pulled all these and checked them against MAME. The first 3 checked were fine the last 3 were actually from an Operation Wolf board and 2 of those were dead anyway. Burned 3 replacement 27c512 EPROMs and tested again.
This time I got a white screen with some garbage on.
After this I plugged in the Fluke 9010 and ran some ROM and RAM tests. The ROMs passed fine but one of the RAMs had failed. The TMM2063 @ IC10 was shot, I used a D4364 as replacement as its the first one I found compatible on a scrap board.
Board still booted with garbage.


All lines on the CPU had frozen.
Checking the game running in MAME I could see that when you first boot the game the whole screen flashes white for a second then the game boots.
I checked the 3 Interrupt line, IP0, 1 and 2, and found that IPL1 was dead, this came from a nearby PAL @ IC36. The PAL was giving an output so I ran a jumper wire to the CPU and booted again.
This time I got a full white screen with the Hi Score at the top and the game ran but only showing the sprite data.


I checked all the ROMs that hold the background data and they all checked out fine. These are MASKROMs and can be read as either 27c301 or a couple of reads as 27c512 with a small modification.
Following the data route from these ROMs I eventually came to a 74LS157 @ IC72. It had dead pins at #3 and #11. Pin 3 should go straight to +5v and pin 11 should come from address bus A10. Ran a couple of jumpers for these and got something a little different, the screen was still mainly white but I could see text underneath it and the sprite colours were now messed up.


Looking underneath the board I found a discoloured track, when I ran the screwdriver over it, it came away from the board looking a little charred.


Only a short jumper required but it was underneath the palette RAM. I started checking the palette RAM and found pin 16 was dead. I removed this 2018 RAM @ IC73 and it tested faulty, replacing this with a 6116 brought the graphics back fully.

Rainbow Islands repair log #1

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Mar 052011

Got hold of a very poorly Rainbow Islands Extra board.
This board had some repair work done previously. There are a few burned out tracks and some dodgy looking wire links.

On power up it just showed a black screen, time to break out the Fluke 9010a.
The Fluke showed I had active interrupt lines. The 68000 CPU has 3 interrupts, IPL0, IPL1 and IPL2. IPL1 and 2 are tied to +5v (they are active low therefore unused here). IPL2 was stuck low.
I traced the line to a nearby 74ALS74 chip and then back to a 74LS273 (IC32). Regardless what the inputs were doing, the outputs were all stuck low. I replaced this and tested, still a blank screen. I check the 74ALS74 again and although all the inputs were now present and correct, its output to IPL2 was still stuck low. I piggybacked a new IC onto it and the game came to life. Replaced the IC.

Now the game booted up I could see that the colours of the character sprites were wrong, mainly black.

This caused me a lot of headache as the colours came good when I put the logic probe on different pins of different IC’s. I determined which IC was partially responsible for sprite colours by interrupting lines on various logic chips. I found that if I toggled pin 9 of IC35 (74LS157) the colours came good more regular. I removed this chip and tested it in my logic tester, it passed but if I put it on a loop it would intermittently fail. Replaced this and the colours were now back to normal.

There is also a problem when the sprites are facing left where it shows a broken character but still facing right. The pictures below shows the broken up boss sprite and broken rainbows when fired to the left.

This ended up being a short on pin 15 @ IC38 (74LS153). This pin was shorted very slightly to an exposed track running next to it. Removing this short fixed the graphics completely and the game is now 100%.
Very pleased.