![]() 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: This fixed the board completely, no other issue were present.Evil Konami defeated again.The battle goes on.As part of troubleshooting his Gradius II PCB, asked me through PM for a summary of my diagnostic procedure when looking at a board. ![]() Probing around again with my logic comparator I found a 74LS74 with bad outputs, once removed it failed : The one didn’t pass the out-of-circuit test failing in address 1073:įinally the board could properly boot and enter in game but with missing graphics and crashing after few seconds all the time : ![]() So a failure in them would explain the missing boot.Not being able to determine which chip was actually faulty, I desoldered both and added sockets: Launching the game on MAME I could figure out that these two RAMs are used by both the main and slave 68000 CPU : So I could concentrate exclusively on CPU board since I know the fault was there for sure.Probing the board with my oscilloscope I found some abnormal activity on a couple of 6264 RAM and 10G : Thanks to my friend Josef who sent me a good Gradius II boardset I could narrow the fault in the CPU board but, before knowing this, during my troubleshooting I found with my logic comparator a couple of faulty Fujitsu TTLs, a 74LS32 on video board and a 74LS157 on CPU board : After Lifeforce, another awesome Konami shoot ’em up on the bench, it’s the turn of Gradius II – GOFER no Yabou :īoth CPU and video board were in great shape but this is what I got once powered it up:īoard sat down on the above message and very rarely showed an ‘ADDRESS ERROR’ or ‘ILLEGAL INSTRUCTION’ message:
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