[Coco] DriveWire issues with Coco 1 F/285 Board

[Torsten Dittel]

I remember darkly an issue my father had on an early (below F) CoCo1 board: 
I was playing with MIDI output (31.25kBaud - e.g. like that of LYRA) via 
the bit banger port. It didn't work reliable on a CoCo1 while it did on my 
CoCo2. When we attached a scope, we figured out that slew rate (both rising 
and falling) of the signal was to small, so single bits (0 or 1) turned to 
be triangles with reduced amplitude instead of the expected rects (with 
full amplitude). That was sometimes catched correctly by the receiver (in 
that case: MIDI keyboard), sometimes not. I remeber my father replaced a 
component with faster response time. As far as I remeber, the output pin 3
(?) of the corresponding PIA is tied to a 741C inverter op-amp. I guess 
it's just replacing that one (I think it was even socketed on the PCB) with 
a current version, but you might want to wait for some comments of the 
hardware gurus out here.

Regards,
Torsten