kikaso
Enlightened
I picked up an "untested" (ie broken) Yie Ar Kung Fu board last year with the hope of learning how to diagnose and repair it. My PCB collection is still growing and I figured I would have to learn these skills eventually.
On boot, the game displays "garbage".
I learned from this very helpful video that garbage on boot up usually points to an issue involving the CPU. I went over both sides of the PCB to inspect for any broken traces. When I didn't find any, I suspected a faulty CPU. I read that the CPU used on these boards is a Motorola 6809 and so I picked up a spare and replaced—same result. I later read that the 6809 in these Konami boards is protected or encrypted and is not easily replaced.
My next step was to probe the CPU. Big thanks to @ShootTheCore for his video diagnosing his Toaplan board as it taught me a lot including that I need to pick up a logic probe and IC test clip. Using the probe, I found that pins 29 and 31 of the CPU were unresponsive leading me to inspect the LS245 bus transceiver at 11C. I checked continuity and ruled out any broken traces between the IC and the CPU and a nearby ROM chip.
Betting that the transceiver was faulty, I placed an order for a replacement chip and socket and voilà!
I am not sure how these chips go bad—I read that they're sensitive to over voltage—but am grateful for the easy repair. In hindsight, I should not so quickly resort to replacing components without first making sure the fault isn't further down the line.
Lastly, I socketed a RAM chip that was poorly soldered in at the factory. Not sure how something like this could leave the Konami quality control inspection but glad to have it properly soldered. I also replaced the electrolytic capacitors given that the board is as old as me.
On boot, the game displays "garbage".
I learned from this very helpful video that garbage on boot up usually points to an issue involving the CPU. I went over both sides of the PCB to inspect for any broken traces. When I didn't find any, I suspected a faulty CPU. I read that the CPU used on these boards is a Motorola 6809 and so I picked up a spare and replaced—same result. I later read that the 6809 in these Konami boards is protected or encrypted and is not easily replaced.
My next step was to probe the CPU. Big thanks to @ShootTheCore for his video diagnosing his Toaplan board as it taught me a lot including that I need to pick up a logic probe and IC test clip. Using the probe, I found that pins 29 and 31 of the CPU were unresponsive leading me to inspect the LS245 bus transceiver at 11C. I checked continuity and ruled out any broken traces between the IC and the CPU and a nearby ROM chip.
Betting that the transceiver was faulty, I placed an order for a replacement chip and socket and voilà!
I am not sure how these chips go bad—I read that they're sensitive to over voltage—but am grateful for the easy repair. In hindsight, I should not so quickly resort to replacing components without first making sure the fault isn't further down the line.
Lastly, I socketed a RAM chip that was poorly soldered in at the factory. Not sure how something like this could leave the Konami quality control inspection but glad to have it properly soldered. I also replaced the electrolytic capacitors given that the board is as old as me.
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