![]() The audio ‘custom’ PCB showed clear signs of corrosion in addition to a missing cap. ‘Realistic digitized graphics’ now restored. I replaced the IC and all was good, colour wise. Scoping the IC, it was clear that the output pin was floating around (when enabled – always check relevant output enable pins are set when scoping to see if an output is alive). You can see in the (partial) schematics that these are used for the colours. This had an effect (normally it shouldn’t as working logic drive outputs can out-do the capacitance effects of your fingers), so I honed it down to a 74LS151. It seemed intermittent and gradual so I took the hack route of putting my hand over the pins on the back of the board. The graphics issue seemed to be at the colour mixer stage – after all layers are combined. It was clear that there were graphics problems and there was no sound (just blips and a lot of heat from the amplifier IC). It’s a good trick – gives you breathing time to see what might be playing up, should the game be capable of running in a faulty state – this board was. Unlikely all this went wrong suddenly one morning.Ī little bit of Googling showed there’s a simple link to make to bypass the watchdog (regards to Caius). Lots of things as it turned out, but initially it just sat in a constant reset within milliseconds of power-on. ![]()
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March 2023
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