(fwd) VT220 keyboard (cont'd)
ard at p850ug1.demon.co.uk
Sun Oct 5 14:50:55 CDT 2008
> >Thanks for the replies, all, especially Tony Duell who had it
Alas I've seen it dar too many times...
> >>This normally means there's a short in the keyboard matrix, as if one =
> >>is stuck down.
> >>What I would do is open up the keyboard casing (there are 2 screws =
> >>the plastic posts/feet) and remove the internals.=20
> >>Connect the PCB to the terminal with the normal cable and power up. =
> >>likely the LEDs will go through the normal sequence and there'll be no=20
> >>error message, which shows the fault is in the keyboard itself.
> >The LED's do indeed cycle when the isolated PCB is hooked up, and
> >eventually "VT220 OK" appears on the screen. So now I either have
So the electronics is almsot certainly working.
> >to find the shorted key (it's pretty dirty in there so blowing
> >with compressed air might help) or just get another keyboard. I
If uou are really keen, you could try to find the shorted key. I have a
pinout of the keyboard tails, it's a 17*8 matrix :
If you're not sure what end the pins are numbered from, the 'Row' lines
go, in order to port 0 of the 8051 microcontroller, the column lines come
from the outputs of the '145 chips E2 (cols 0-9( and E3 (10-17)
What you need to do is check each Row connection to each Column
connection with an ohhmeter. See if you van find one that's low
resistance. When you do, let me know the row and column and I can tell
you which key that is.
You might then be lucky in that removing the key and lifting the leaf
spring away from the membrant might cure it. But alas it rarely does.
> >won't try and wash it after reading the warnings here.
> >BTW I see one on ebag right now (190254818657) but it's a
> >"VT220-Style" unit, made by another manufacturer. Think it'd work
> >with a real VT220?
I doubt it. Many manufactuered copied the keyboard layout and design but
not the interface.
I thought LK201s were not that hard to find.
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