Akai ME-20A Schems/hacking

[DCMagnuson at aol.com]

Hello list,

I just picked up a used Akai ME-20A arpeggiator.  It's a very simple unit, 
but pretty effective.  Although this unit is a MIDI arpeggiator, it doesn't 
accept MIDI clock info.  It merely has a pot to adjust the speed of the 
arpeggio.  All this talk about retriggering S&H circuits got me thinking....

Basically I want to hack an external trigger into this thing, and drive it 
from a MIDI to Din-Sync converter... I could then theoretically make it 
respond to start/stop and tempo.  I figure I can use a divider circuit to get 
the appropriate delay step length (quarter note, eighth note, etc)

Anybody have a set of schematics or ideas about acheiving this?  I haven't 
gotten as far as tracing the circuit yet, but I popped the lid, and the only 
IC's I see are 

D flip-flops, (one 20 pin DIP)
Hex Schmitt triggers,  (one 14 pin DIP)
Sharp PC-900 (8 pin DIP, physically located near the MIDI jacks, so I'm 
assuming it's an opto-isolator)

and 2 NEC chips that I can't identify.  
One has 8525H7 and D7811G 243 (64 pin)
the other 8510XD and D446C-1 (24 pin)

Any ideas about the unknown ICs?  I'm fearing that the clock is controlled by 
a microprocessor... am I right?  I was hoping for a pulswave LFO in there, 
but struck out.

If worst comes to worst, I'll trace backwards from the clock LED in the 
arpeggiator to find a trigger source, buffer it, and use the arpeggiator to 
drive my analog sequencers... but that still won't sync me to MIDI-land... 
but maybe I need to go all analog for a while anyways ;)

Thanks in advance
Dave Magnuson
Independent Music Site
http://www.indiemusicsite.com