DEC LK201 keyboard

From: Allison J Parent <allisonp_at_world.std.com>
Date: Wed Oct 22 10:36:13 1997

<Several seem to have the same problem in that the 4 status
<LED's all light up, but the keyboard does not respond.
<Has anyone encountered this problem and repaired the
<keyboard?
<
<Does anyone have a schematic for this keyboard that they

You don't need it. There isn't much to see.

Probe the board for +5 and -5 power if either is missing track it backwards.
the keyboard is powered off +12v from the system and there is a +5v
regulator on the board (7805, TO220) if that's ok then check for -5v(or so)
on the RS423 driver chip(9636). If that's there then probe the 8051 for
valid reset and crystal osc running. There isn't much to them and the key
is the 8051 microprocessor, if it's fried then look for a keyboard that's
mechanically trashed. Coffee, mechanical damage and ESD are the common
failure mode.

Allison
Received on Wed Oct 22 1997 - 10:36:13 BST