I was fortunate enough to obtain an original Taito Rainbow Islands PCB recently, which of course was not working.

I tested the PCB in my Supergun and was presented a solid white screen;

Checking the 68K CPU, the clock was fine, and RESET line was held high, there was activity around the CPU which indicated it was trying to execute code.

The work RAM looked good, so I checked the two 62256 SRAMs that the PC080SN custom uses for all backgrounds/tiles.  The outputs looked bad on both.  I also noticed that when I touch the pins on the SRAMs the screen display changed.

I removed the SRAMs (IC3 & IC4) and confirmed they were bad in a RAM tester.

I installed sockets for easy maintenance and replaced with fresh SRAMs;

The PCB was now running, but had some issues with background/tiling;

Speaking to my friend Porchy about this fault, he stated that it appeared that Bit 4 (counting from 0) was stuck LO, and that the PC080SN custom was responsible for it (RAM lies at address 0xC00000 – 0xC0FFFF).

I was hopeful it was not a fault within the custom, and eventually after probing found that IC12 (74LS373 Octal Latch) Pin 9 was stuck LO (should have been pulsing LO/HI).

I removed the IC, installed socket with fresh 74LS373 and was greeted with a fully restored display;

I did notice however that sometimes the display would lose all the BLUE.  So my attention turned to the TC0070 SIP custom that handles RGB.  I found a cracked pin (highlighted with Red arrow), which I resoldered to resolve it;

It was now running perfectly, except for the sound which appeared to be absent totally.

I checked the Z80 CPU which handles sound, and it was definitely running code.  So I checked the TL074 op-amp at location IC67 and found it appeared dead (no output, but probing input I could hear the sound!).  So I removed it, installed socket with fresh TL074 to fully restore the sound;

Many thanks for Porchy for his help with this repair.

Another Rainbow Islands Log to come very shortly, solved with help from my new friend Caius.

 

 

 

 

I got a couple of Chequered Flag PCBs for a repair.Here’s the first:

The MASK ROM test reported an error on a character ROM at a certain location:

which caused some garbage on screen:

Launching MAME I could figure out the ROM reported as bad was the one @N16:

Device itself was a non 32 pin non-JEDEC 27C1000 mounted on a custom socket in place of the classic 1Mbit 28 pin MASK ROM.So I read it and it matched the one on MAME sets.Probing it I found that its pin 28 (A13) was silent,I traced it back to the a near custom marked ‘051316’ that addresses the entire character ROM :

A dead address line means that the IC has an internal fault so my only option was to replace it and this is what I did taking it from another dead board:

With a good custom the MASK ROMs test successfully passed and all GFX issues vanished:

The second PCB :

had slight sprites issue.Here’s a comparison with a MAME snapshot (on the left):

A visual inspection of the board revealed some lifted pins of the two ASICs sprites generators:

A reflow was enough to restore correct sprites:

End of (double) job.

I got this mint The Outfoxies PCB for a repair from my friend Zoran :

For the uninitiated it’s a fighting game released by Namco in 1994 on Namco NB-2 hardware.The board ran well but had some inputs issue regarding the player one.Down input was not responding while left one was intermittent.This was confirmed also by switch test :

Also in this Namco hardware (like the NA-1/NA-2 and NB-1 ones) the inputs signals from JAMMA pass for first through some SMD EMI filters (which suppress high frequency interferences).Using a multimeter revealed that JAMMA pin 19 and 20 parts side had continuity with the inputs of the EMI filter @FL12 but the outputs lost their connection with the pads:

Restablishing the lost connection with a bit of AWG30 wire fixed the issue completely: