Introduction During the late 1980s, Namco set out to create the world s largest arcade game. The result was Galaxian3: Project Dragoon; a 28 player behemoth that debuted in April 1990 at the International Garden and Greenery Exposition in Osaka, Japan. Codenamed GH-28, it featured real-time, flat-shaded 3D graphics, powered by hardware derived from the System [ ]
Problem Tilemap layer corruption: Diagnosis With Raiden II and similar Seibu PCBs, the first thing I check for are loose legs on the various fine-pitch customs. Despite some mild corrosion on the legs, all were fine. Probing around the area in the upper left corner where the BG-1/BG-2 mask ROMs area, I noticed weak signals [ ]
Problem Game plays but displays only colourful vertical bars: Diagnosis Battletoads is one of three arcade games to use the TMS34020 Graphics System Processor (GSP), the other two being Revolution X and Metal Maniax. The GSP appears to handle the foreground and background layers, while an FPGA draw sprites into a framebuffer. Being a 90s [ ]
Problem Distortion at top of screen: Diagnosis As Gyruss is a vertically-oriented game, the distortion is actually present at the beginning of each scanline. The distortion appears to affect the first four pixels of the tilemap layer. The pixel data for the tilemap layer is contained in ROM 2H. The tiles are 8 8 at 2bpp, [ ]
Problem No sprites displayed: Diagnosis Buggy Boy is a game close to my heart as it was one of the first I added to MAME back in 2006. It is a very large, incredibly complex boardset: Luckily, full schematics are available. Probing around the sprite hardware (TC-042 sheets 1-4) with a scope, I found that [ ]
Problem ROMs U26-U40 reported bad. Diagnosis The ROM board tested OK with a known-good CPU board, so the problem was somewhere on the CPU board. The bad ROMs are Image Memory ROMs, which are accessible by the DMA chip on the CPU board. The image memory data bus is 32-bits wide, with ROMs U25-U40 occupying [ ]
Problem Bad sound. Diagnosis The game would occasionally sound two bongs on boot, which would normally indicate a U10 sound ROM error. However, these bongs were played at a lower pitch than usual and sometimes the game would emit an ear-piercing screech instead. I verified ROM U10 out of circuit against the known-good checksum. It [ ]
Problem Game would not retain settings after exiting test mode. Diagnosis One might suspect that game settings are stored in RAM backed up by the CR2032 battery and super capacitor on the PCB and that the RAM is faulty. However, there is a 93C45 serial EEPROM underneath the I/O PCB which holds the settings: The [ ]
Problem Displays garbage, watchdog resetting: Diagnosis I agreed to look at a friend s Donkey Kong Jr. boardset: I ve never worked on any Nintendo boardsets before but my friend kindly supplied a power supply and JAMMA adaptor so I wouldn t end up spending more time wiring it up than actually diagnosing and repairing it. I attached [ ]
Problem No motion objects (sprites): Diagnosis I was given a Primal Rage boardset to look at, which I was not especially looking forward to given its size and complexity: Unfortunately I had put my own Primal Rage boardset into storage, so I would not be able to resort to swapping parts over (there are quite [ ]