My friend ‘robotype’ sent me some boards for repair.Among them there was this a “Kid no Hore Hore Daisakusen” PCB (キッドのホレホレ大作戦^? lit. Dig Dig Kid’s Epic Battle), a pretty obscure (for me, at least) game manifactured by Nichibutsu in the 1987 (released in the Western market as “Booby Kids”):

Board uses, surprisingly for its age, JAMMA pinout so I could power it up without the need of building an adapter as I first thought.Here is all I got, some static garbage:

This is clear sign that the CPU is not running so for first  I probed the 68000 main processor.Starting my checking from pin 1 all was stuck LOW or HIGH until I came to CLOCK (PIN15), this was completely silent.I traced it back to a typical clock circuit made of an inverter 74LS04 and a 74LS74 as divider.These ICs were good but when I went further back till to the 16MHz quartz I got this on my scope:

It was completely dead!Replacing it brought PCB to life again.

Who of us has not played at least once Xevious?

Xevious is a vertical scrolling shooter arcade game that was released by Namco in December 1982.It runs on Namco Galaga hardware. In North America, the game was manufactured and distributed by Atari.

I had on my bench the Namco version:

Board booted correctly, game was fully playable but sprites were missing some lines and also playfiled got some issues:

All GFX customs (the sprite positioner ’12XX’, the object RAM addresser ’04XX’ and the GFX data shifter and mixer ’11XX’) were OK since I swapped them with ones of my Galaga/Gaplus boards.Luckily Namco released schematics for this board so for first I checked the part of circuit involved.All was good until I come across this section:

As you can see there are six 74LS161 counters that take DATA from one 2128 SRAM @2S (addressed by the custom “04XX”):

Three 74LS161 address two of the four 2149 RAMs @5M and 5N:

When I went to probe the two 2149 RAM @5N and 5M I found four address lines (PIN3-6) stuck LOW.As I said before, these are addressed by a counter @5S so I went to use my HP10529A logic comparator on it.All led corrisponding to outputs turned ON while all inputs were correctly working.Desoldered and tested it out-of-circuit confirmed it was bad:

Fitted a good 74LS161 restored correct graphics.

 

With this repair we conclude the May season of logs.See you hopefully next one!