6 Slot – Memory test on power up giving error
Address Write Read
00008000 5555 55FF
Checking with Mame, the memory chips in question were only small, so looking at the board revealed two DIL 5814’s. Chip select signals to these were toggling as expected, so I needed to identify which ram chip was which. Using the test probe I shorted pins 11+12 on one chip, powering on the board now gave read as 51FF so I was looking at the wrong chip. Replacing the other (with a 2018-35) sorted the problem.
Glitched graphics. Screen changes as board is flexed. Moved around board pressing chips until pressing the custom surface mount chip at B6 changed the effect. Noticed that the corner most pins had come up from the board. After an unsuccessful effort to resolder them, I used some enameled 38 swg wire to solder from the…
Capacitor burnt. (game board), particularly at C37 the capacitor was showing signs of extreme heat. Replaced them all with 22uF 25V axial electrolytics. No Speech / Some SFX missing. (game board) Output from speech chip SC01 was OK, as was output from IO Custom (X3). checked transistors in output stage and 2N4401 was faulty. (Q2)…
One of the guns on a Time Crisis 2 was no longer registering shots on the screen. Following checks on wiring, cleaning lens, etc. it appeared that the optical sensor (opto) was dead. This is a small PCB in the gun, 2421961100, pictured above. I couldn’t find any schematics or information about the parts used,…
Boots up, and plays, but incorrect sprites – most noticeable little bug changes into ‘END’ at one point. Check 74ls138 at 8n, controlling graphics banking, and pins strobing. Replace chip and now uses correct sprites. Quiet missile sound and explosion sound. Both of these effects use the op-amp chip, LM324 at 7T. Replace this chip…
Crashing game. Game woud start attract mode, but shortly after would crash and boot loop. Entering test mode (hold player 1 start button whilst switching on) and it would pass first time around, but fail at random addresses on subsequent runs. The /WAIT signal on the main Z80 is handled by the IC at E2…
Totally dead, no screen display (blank white screen). For this I used the Fluke Z80-S2650 adapter to check out the ram and rom, and located two errors. The rom mapping was incorrect, with a large range of locations returning random values. Examining the board (since I have no schematics), all of the chip select lines meet up…