Vintage Synth Repair

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