Comatose JX3P - 8051 CPU issue?
2009-02-28 by Pascur
I have a JX3P that wasn't used for a few years. When first turned on, some of the leds came on but it wouldn't respond to button or key presses. I replaced the battery, but the only difference that made is now the leds don't come on any more either! I've been working my way through it with a scope and the only thing I've found that seems odd is that the RD and WR signals from the 8051 CPU are both a constant +5V, rather than the strobe signal I'd expect. Interestingly, when I put the scope onto the WR test point, the LEDS briefly flicker into life before going dark again. Any idea why RD and WR wouldn't be strobing? There's definitely a clock going into PSEN. Or am I on the wrong track entirely? Thanks, Lindsay