![]() Neatly (word?) enough, the starfield and explosion noise are both generated by a pseudo-random generator consisting of some '164 shift registers. This article on Marco's Arcade gave me some quick tips on fixing this. Galaxian (Midway): Missing the stars and the explosion noise when the ships get hit. Seriously, the sound on this thing is all generated from 555 timers. I soldered a little jumper to a nearby ground and all the beautiful analog sound returned. I actually still don't know where the break is, but it wasn't connected to the rest of the GND net. Basically, after verifying everything should be working, I happened to notice that one of the main analog switches (CD4066) had a floating GND pin. I spent a few days looking at the terribly scanned schematics and combing through the MAME drivers (which were super helpful). Made an adapter to read the color PROMs and they are "Pioneer Balloon" PROMs, so someone did a conversion and didn't quite finish! For the missing sound effects, I started checking the schematics and quickly found that one of the '161s (IC58) wasn't outputting the carry bit, which is needed. Nibbler: Wrong colors and missing half the sound effects. Judging from the flux around this resistor, it was replaced at some point with this incorrect value. The sound effects all get to the final amplifier by way of a simple resistor-based mixer, and one of the resistors was 47k instead of 4.7k, giving that sound effect a much larger amplitude. Replaced with a spare, audio returns! One of the sound effects was super loud compared to the others. The 6502 that controls the audio seemed dead and hot to the touch. (to be continued, forget which board I was working on.)Ĭook Race: No audio. I pulled a few romsets and found that by inspecting other ones. Checking the audio cpu ROM, it gave me no matches on the mame database. The audio CPU would work at startup for a moment then go silent, albeit without /HALT or /RESET. It would scream at me when I first turned it on, then nothing. Also a fix on the C-board, this time by reflowing the solder on the big CPS B-12 chip. ![]() ![]() MERCS B-Board #1: No video. Actually a fix on the C-board, simply one of the inductors had a broken leg. ![]()
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