Demon's World repair log #3

Recently I received for repair this Demon's World PCB (a platform game released by Toaplan in 1989,  known also as Horror Story)

The owner told me that the board originally was missing the chip marked 'GXC-04' so he bought the replacement I designed time ago :

 You can read more about this custom chip and my replacement here :

Toaplan 'GXC-0x' reproduction

But, even with the replacement fitted, the board was not working so he decided to send it to me to have a look.Indeed the board was not booting, only a raster of wavy lines on the screen at power-up :

As usual I did a visual inspection of the board and found a deep scratch on component side :

Testing the continuity with a multimeter revealed four broken traces, I promptly patched them with some AWG30 wire :

This made the board booting up finally :

The game was fully playable with sound but sprites were corrupted :

Sprites data are stored in four 28 pin 1Mbit MASK ROMs :

 

I dumped them and one device turned to be empty :

This was a clear sign it was bad and needed to be replaced.In place of of these 28 pin 1Mbit MASK ROMs you can use non-JDEC 32 pin 1Mbit EPROMs (like 27C1000, 27C301 and other).The PCB is already set up to accept 32 pin EPROM as you can see from below picture  :

 So it was only matter to install a bigger socket and program a proper EPROM (Hitachi 27C301 in my case).This is what I made :

This fixed the sprites issue :

 No other issue found so board 100% working again.Another successful repair.

'NMK-111' and 'NMK-112' reproduction

The 'NMK-111' and 'NMK-112' are two custom chips found on many arcade PCBs from NMK manfacturer.

They share the same QFP64 package :

Technically speaking the 'NMK-111' is used for latching RGB output (just before the 'NMK-007' R/2R DACs) and handling palette RAM. It's also used for handling background VRAM.The 'NMK-112' is used for OKI MSM6295 audio samples ROM banking.

Some time ago I sent 'Furrtek' (https://x.com/furrtek) a couple of chips, he promptly decapped and imaged the silicon dies.After some time 'Recreativos Piscis' (https://x.com/Recre_Piscis) identified the cells of the dies making schematics of the internal structure and writing Verilog code of it.The last step was making a proper replacement of the chips, this is what I made using the castellated half holes design in order to mimic the QFP64 package.I chose a small CPLD to embed the logics :

 

Both replacements worked fine at first try.Here is testing of the 'NMK-111' reproduction as RGB latch on a Macross PCB :

Here is testing of the same reproduction as background VRAM handler :

Here is testing of the 'NMK-112' reproduction : 

A huge thank again to 'Furrtek' and 'Recreativos Piscis' for their brilliant work without which this result would not have been possible.

Konami '0005292' reproduction

The  Konami '0005292' is one of the varios custom ICs you can find on Konami 'GX400' arcade system, more precisely on the video board.You can read more about the GX400 hardware here :

Konami GX400

The '0005292'comes in a SDIP64 package :

 

Technically the chip is a counter/clock divider providing all video timing for the system, here's pinout from Nemesis schematics : 

For my reproduction job I used a Salamander bootleg where the functions of the chip have been reversed by using simple 74 logics.After identifying the equivaent circuit I made a replacement based on CPLD :

After some timing clock adjustement the replacement worked fine, here is testing on my Black Panther PCB :

In the next future I will look at the other GX400 custom ICs with the aim of doing a replacement of the whole video board, stay tuned for further updates.

Thundercade repair log

Got for repair an original Thundercade PCB, also known as Twin Formation and 特殊部隊UAG, a vertical shooter developed by SETA and released in 1987.Board was in very good condition :

When I powered it up I got a black screen as the power supply of my test rig had gone into protection so I turned off the power.Using a multimeter I found there was a dead short across GROUND and +12V, the measurement was taken with the probes on the protection zener diode just near the egde connector :

I also noticed there was some burn marks over the sound amplifier heatsink, this was a clear sign of some heavy event (overcurrent or overvoltage on the +12V line)

Anyway, after I removed the zener diode, the short was cleared so I could power the board up again.Game was playable with sound too but sprites were glitched :

Sprites data are stored in eight 2Mbit MASK ROMs :

I dumped all of them (as 27C400 and then I splitted the files in two halves).Doing a MAME ROMs compare all the files were matching the existing set except the one marked 'UA0-10 W51'.To have  confirm I replaced the MAME dump with mine, I launched the emulator and could reproduce exactly the same issue :

 

Since there are no direct replacement of 40 pin 2Mbit MASK ROM I programmed a 27C400 EPROM doubling the MAME ROM file into the progrmmer buffer :

This fixed the issue and board completely.Repair accomplished.