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!

 

Another repair from the same PCB batch of previous logs (three in a row…), this is a Lethal Enforcers PCB in mint condition:

Once powered up I got this static screen:

and a ticking sound sign that board was watchdogging.In these cases first thing to check is the main CPU.Probing pins of the HD63C09E CPU (6809 compatible) I noticed that R/W (PIN32) was completely silent.This is  the control line through which CPU decide if write (active LOW) or read (HIGH) DATA onto the DATA bus.The fact that it’s an output and  it was inactive made me very suspicious.HD63C09E datasheet says that R/W line can be made in high impedance  if BA (PIN6) is HIGH but this was not my case since BA was pulsing LOW.

/WE line of 6264 WORK RAM stuck high.This is generated, indeed, by the /WR signal (PIN32) of main HD63C09E CPU through the BUS master arbitration circuitry.This lead me to desolder the CPU from board and try it in another board.It was really faulty.I socketed it too for easy maintenance:

With a good CPU fitted game obviously booted but showed jailbairs over backgorunds:

This a common problem on this Konami hardware which uses graphics custom ASICs in QFP package.Specifically Lethal Enforcers uses sprite and tilemap generators and these work always in pair.My issue was located on backgrounds so I went to inspect the pair marked 054156/054157 and found some lifted pins on the latter @S8:

I promptly reflowed them with my hot air rework station and goodbye jailbairs!Game 100% fixed.