tindle@ms.uky.edu (Ken Tindle) (03/13/90)
Hello again, I'm the one who posted recently in need of a way to activate
the video circuits of an Osborne 1. I got mail from these kind folk...
Steven Russell <SRUSSELL@uoneuro.uoregon.edu>
David Goodenough <dg@pallio.UUCP>
Les Flodrowski <les@uwovax.uwo.ca>
Al Jones <acj@cs.rochester.edu>
Bob Mesenbrink <rlm@druhi.att.com>
... and would like to thank them.
Taking their advice, I called Worswick Industries at...
Worswick Industries (619) 571-5400
4898 Ronson Ct. Suite H Hours: M-F 9-6 PST
San Diego, CA 92111
... and found they still sell card-edge to composite video adapters for
$19.00. Sorry, Les, no "official" shunt; but this dude activates the
internal monitor as well, so will get you going regardless.
I received today an adapter which works, er, sort of. The picture lacks
contrast and is not very stable, however. So I've ripped it apart, to have
a look at its guts.
True to form, and as expected after reading my e-mail, the thing connects
all the top pins on one side to the bottom corresponding pins on the same
side, to turn on the internal monitor. It's interesting to note the card
edge fingers are mirrored, so one can put the connector on either way, and
it'll work. What consideration on Osborne's part! Too bad they didn't
just put feedthroughs on the *&#@$% motherboard to begin with!
The thing turned out to be eating five signals- +5V,GND,Hsync,Vsync,VIDEO.
The H and V sync pulses are generated by an 'LS221 dual one-shot, whose
periods are not adjustable. Their outputs are connected by divider to the
video signal, and buffered by a transistor, feeding an internal 75 ohm load.
The instability is (apparently) being caused by incorrect sync timing, and
the lack of contrast because the monitor has a 75 ohm load too, which loads
the transistor too heavy and makes the overall signal too small (this isn't
helping the stability either, if the monitor can't *find* the syncs, they
may as well not be there)! So I'm gonna try ripping out a resistor and
adding a pot, to replace the fixed resistor controlling timing.
If I ultimately can't figure this out, I'll "cheat" and buy a solution!
It looks very doable (at first flush) to get an IBM mono monitor signal
from the card edge; then you could use the flotilla of these monitors
one can often find laying around. Nobody wants to play with composite
much anymore. :-(
I also got info for a user's group I'll look into:
415-755-2000
First Osborne Group
P.O. Box 3474
Daly City, CA. 94015-0474
These folks are reputed to have mucho goodies, and concerning CP/M machines
of *all* flavors, too!
Cheers.
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INTERNET:tindle@ms.uky.edu | "Could you please continue the petty bickering?
BITNET: tindle@ukma.bitnet | I find it most intriguing." --- Data,
Ken Tindle - Lexington, KY | Star Trek, The Next Generation, "Haven"
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