Caius

Sep 242019
 

This is my own implementation of the Konami ‘082’ custom IC with the use of simple logic gates.Original part is a 28 pin 600mil IC found on many PCBs of 80’s.As often happens with most of Konami custom ICs it comes with scratched-off part name:

I was able to shrink my board layout to almost same dimensions of original part by using TSSOP devices :

Perhaps not the neatest design, you may call it a ‘poor man’s’ version of the existing CPLD based solution but it works fine and I’m happy with it.Here’s final testing on a Track & Field PCB :

 Posted by at 8:45 am
Sep 212019
 

Received from Austria this Heavy Barrel PCB, a run and gun arcade game released by Data East in 1987 :

Board was in really good shape and game was fully playable too but lacked of sound :

Using an audio probe revealed no sound came out from analog circuit hence the fault was of digital nature.Audio system is ruled by a 6502 CPU located on top board :

Its pinout :

Checking it with a logic probe revealed that the /NMI line (pin 6) was asserted as well as two address lines were stuck low (A12 and A14)

A non-maskable interrupt triggered is usually due to some hardware failure hence for first I dumped the ROM containing the audio code (located on bottom board), it turned out to be good.Then I focused on the RAM accessed by the 6502, a 8K x 8-bit device (6116 compatible)

As soon as I piggybacked it with a good chip I got some random sounds played.The scope revealed weak signals on some data lines of the RAM (a good signal on the left of below picture for comparison)

I removed the IC :

And sure enough, it failed the out-of-circuit testing :

New chip fitted :

Sound was thus restored and another board fixed.

 Posted by at 10:31 pm

Namco ‘CUS98’ reproduction

 Reproductions  Comments Off on Namco ‘CUS98’ reproduction
Sep 102019
 

As someone may recall I’ve recently done a reproduction of the custom ‘CUS99’ used on Namco PCBs :

Namco ‘CUS99’ reproduction

After done it I thought it was good to take into account its “companion” too, the ‘CUS98’  which most times come along with the first.Package is pretty the same but with two further pins than ‘CUS99’

 

But functions are totally different and,  as Rolling Thunder schematics suggest,  the main one is to generate the master reset :

Secondary functions are coin counters and lockouts handling as well as lamps driving, it seems only few games (like Pac-Land and Gaplus) use this last feature :

I was obviously interested in reproducing at least the reset generation function which is essential for correct operation of the PCB  (but it seems Rolling Thunder can boot into game also with a missing ‘CUS98’).Therefore, as usual, I studied earlier Namco hardware where the custom had not yet been used and I came to a prototype developed on a breadboard:

The protoytpe worked pretty good :

Hence I developed a proper board :

Final testing on a Pac-Land PCB:

As said some functions have been intentionally omitted favoring the needed ones (watchdog circuit ad reset switch were implemented too).This will at least allow to save PCBs with a faulty/broken or missing ‘CUS98’.

 Posted by at 8:10 am

Rapid Hero repair log

 PCB Repair Logs  Comments Off on Rapid Hero repair log
Aug 292019
 

Got for repair this original Rapid Hero PCB, an obscure vertical shoot ’em up released by NMK in 1994 and a very sought-after board :

The board booted up but some sprites were affected by jailbars :

Besides, an entire music track was missing or sometimes corrupted as well as some sound effects:

 

The board had some sign of previous repair on solder side :

This is the area of the ‘CN1’ and ‘CN2’ connectors where the ROM board, which contains all the game code and data, plugs into the mainboard:

The repairs let assume a weakness and subsequent failure of the headers connections probably due to repeated disconnections and insertions of the ROM board.So I checked with a multimeter in continuity mode all the traces from the ‘CN1’ header and found another broken one that I promptly patched :

This fixed the graphics, no more jailbars on sprites :

Now the sound issue.

The audio circuit was previousy reworked, one of the OKI MSM6295 was likely replaced and one trace was repaired but this was not the culprit :

I noticed that if I pressed the ROM board on the ‘CN2’ connector some of the missing sounds were restored.I checked traces from ‘CN2’ to mainboard and found two missing connections to the ‘NMK112’ custom ASIC (responsible of  bankswitching the sample ROMs of the two OKI6295 ADPCM chips)

I patched the traces with some AWG30 wire:

Sound was totally restored and board 100% fixed.Repair accomplished.

 

 

 Posted by at 10:57 am

Irem ‘KNA6032701’ reproduction

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Aug 112019
 

Another custom IC successfully reproduced, it’s the Irem ‘KNA6032701’ , a 42 pin DIP 600mil IC used on M62 (Kung-Fu Master, Lode Runner, Spelunker and other), M75 (Vigilante) and M72 (on some  type of ‘M72-B-D board) hardware

As usual I reproduced it my way by observing how it was reverse-engineered on bootleg boards obtaining in a board layout with pretty same dimensions of original part :

Testing on a Kung-Fu Master PCB :

 Posted by at 10:26 am