![]() Battery acid will need to be cleaned with vinegar and Q Tips. Rust should be scrubbed off with a fiberglass brush, and the affected solder joints should be reflowed. If you find loose components, try removing and then reinstalling them. Check both the top side and bottom side of the PCB carefully for physical damage. Look for scratches, loose chips, rust, missing components, bent legs, etc. Pay special attention to any repair logs where they treat the same symptoms your board is having - that's a great focus for your troubleshooting.ģ) Inspect the board carefully around the affected subsystem. There's also a three board Twin 16 variant, but it's rare. ![]() Your problem seems to be CPU related so you'll want to focus on the top CPU board. It looks like Twin 16 usually has two boards - the top CPU board with two 68000 Main CPUs, the Z80 sound CPU, the audio hardware, the I/O hardware - and the bottom Video board with the background tile generators, sprite hardware, and fixed text hardware. There's some repair logs for this hardware here: With your Gradius II, I assume it's a Konami Twin 16 hardware conversion - that hardware is also used for Cue Brick, Dark Adventure, Missing In Action and The Final Round. The MAME driver source code can also be a good source of identifying which EPROMs feed which systems, along with other info. The main CPU and supporting EPROMs, RAM, and TTL logic tend to be in the center of the PCB, and video (usually custom chips fed by EPROMs and TTL logic) are often around the edges on a single PCB. The audio subsystem (CPU, RAM, EPROM, music synth) will be located next to the audio amplifier and volume dial. Generally speaking, the subsystems usually "clump" together - control I/O and pallete RAM will be close to the JAMMA connector. Ideally, you want to be able to identify where each subsystem of the game is physically located on the PCB - CPU, audio, background tiles, sprites, pallette and I/O. Remember that several games often use the same or similar hardware, so be sure to look up schematics / logs on those games as well. ![]() That points to an issue with either the code the CPU is executing (EPROMs), the CPU work RAM, or the TTL logic chips between the CPU and work RAM - so you'll want to focus on the CPU subsystem.ģ) Research the board and identify where subsystems are located physically on the PCB.Īre schematics available for the board? Are there repair logs from other people working on the same board? Since your board isn't proceeding to the results screen, one of the two main CPUs is probaby crashing. It looks like the RAM ROM check normally proceeds to a summary screen where it lists Pass & Fail results. ![]() The graphics don't look corrupted though, so that's a good thing. With your Gradius II, the board starts up and hangs on the RAM ROM check. If it has corrupted audio, is it music, SFX or speech? How does the malfunctioning board behavior compare to a properly running board in MAME? Is the board not starting up at all? Does it startup but fail a diagnostic check? Does it boot up and run, but have corrupted audio or video? If it does have corrupted video, is it background tiles, sprites, or overlay (fixed) text. Some boards won't boot up normally if a Test or Halt DIP Switch is enabled.Ģ) Identify the malfunctioning subsystem. Some boards need a DIP switch selected to enable Test Mode. Some boards need a little more juice than 5.0V to run, but don't exceed 5.15V if you can help it. A decent entry-level EPROM programmer costs $200.Įventually, you'll also want soldering and desoldering tools - you'll need them to remove faulty components from the board to replace them.ĭecent entry-level soldering tools start at about $150.ġ) Make sure all DIP switches are set to OFF, and that the supply voltage is between 5.0V and 5.15V. I made a tutorial video on using a logic probe to test an EPROM here:Įventually, you'll want to have an EPROM programmer - it lets you dump ROMs, program new EPROMs, test logic chips, and test RAM chips. A decent starting logic probe can be obtained for around $20 from Amazon. You'll want to have a logic probe - it lets you see the logic activity for each line on each chip. A decent starting multimeter can be obtained for around $20 from Amazon. Use it to test for voltage levels on chips and for continuity on traces. I don't know what your current knowledge level of electronics troubleshooting is, so I'll try to explain things as thoroughly as I can without getting too far into the weeds.Īt a minimum, you'll want a digital multimeter. Here's the rundown on my process when troubleshooting a board. I ended up writing a short essay, and we both agreed that the info may be useful for others so here it is: As part of troubleshooting his Gradius II PCB, asked me through PM for a summary of my diagnostic procedure when looking at a board.
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