30 Sep
2008
30 Sep
'08
1:20 p.m.
I turned on my VT220 for the first time in nearly a year. The
screen says "VT220 Keyboard Error 4", all four green LED's (on the
top right of the keyboard) stay lit, and nothing appears on the
screen when I type.
Disconnecting and reconnecting the coiled-cord between the
keyboard and the terminal causes a cursor block to appear on the
screen, but the keyboard is still locked and the LEDs stay on.
Power-cycling the terminal shows the same error message.
However, the boot prompts from the 11/23+ are displayed normally,
so the receive part of the terminal at least is working.
Where should I start looking, before replacing the keyboard?
thanks for any hints
-Charles
1 Oct
1 Oct
3:27 p.m.
On 30/09/2008 18:20, "Charles" <charlesmorris800 at centurytel.net>
wrote:
I turned on my VT220 for the first time in nearly a
year. The
screen says "VT220 Keyboard Error 4", all four green LED's (on the
top right of the keyboard) stay lit, and nothing appears on the
screen when I type.
Disconnecting and reconnecting the coiled-cord between the
keyboard and the terminal causes a cursor block to appear on the
screen, but the keyboard is still locked and the LEDs stay on.
Power-cycling the terminal shows the same error message.
However, the boot prompts from the 11/23+ are displayed normally,
so the receive part of the terminal at least is working.
Where should I start looking, before replacing the keyboard?
Start with the keyboard - error 4 means the VT can't detect it.
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?
4:20 p.m.
I turned on my VT220 for the first time in nearly a year. The
screen says "VT220 Keyboard Error 4", all four green LED's (on the
top right of the keyboard) stay lit, and nothing appears on the
screen when I type.
Disconnecting and reconnecting the coiled-cord between the
keyboard and the terminal causes a cursor block to appear on the
screen, but the keyboard is still locked and the LEDs stay on.
Power-cycling the terminal shows the same error message.
However, the boot prompts from the 11/23+ are displayed normally,
so the receive part of the terminal at least is working.
Where should I start looking, before replacing the keyboard?
This normally means there's a short in the keyboard matrix, as if one key
is stuck down.
What I would do is open up the keyboard casing (there are 2 screws under
the plastic posts/feet) and remove the internals. The keyboard has 3
'tails' that are fixed to the PCB by little metal clamp-things -- bend
up the 4 tabs on the underside of each one and remove them. If you like
you can remove the PCB from the keybaord frame by removing the clip on
the top of the voltage regulator (TO220 package) and the screw through
the LED mounting block.
Connect the PCB to the terminal with the normal cable and power up. Most
likely the LEDs will go through the normal sequence and there'll be no
error message, which shows the fault is in the keyboard itself. This is a
membrane contact unit with the key housings head-staked in place and with
leaf springs under each key. I've never managed to get one back together
after taking it apart :-(.
I suppose you could chack if any of the keys are mechanically stuck (the
keys themselves can be removed by carefully twising them to free the
locking barbs), and see if any of the leaf springs look bent. But I guess
it's most likely you'll be looking for a replacement keyboard switch
assembly or a complete keyboard (in the latter case keep all the bits of
the old one, just in case you ever find one with a problem on the PCB).
-tony
5:29 p.m.
Speaking of keyboard trouble: do NOT attempt to wash an LK201 keyboard in any kind of
liquid. The "switches" are just membrane thingies, and they are not even close
to liquid-tight. Any washing will put liquid inside your keyboard, wrecking it. I found
this out the hard way (after spilling stuff on the keyboard -- washing it only made things
worse).
It may be possible to dismantle those switches, but it looks hard. It may be worse than
that...
paul
5:41 p.m.
It may be possible to dismantle those switches, but it
looks hard. It
may be worse than that...
Dismantling one is easy -- I've mentioned how to remove the PCB and he
kyecaps. After that you ahve to cut wasy all the heatstakes, at which
point the key housings nad leaf springs fall off and you can sepaerate
the memberane layers.
Ressambling one is hard. Very hard. So hard that I never managed to do it.
The problem is that there's not enough length left in the heatstake pins
to form them over again. The walls of the key housings are not thick
enough to drill them out and assemble them with screws. DEC never supplied
spares for the keybaord switch assembly (even when the LK201 was a current
product) so you couldn't get new hosuings with long heatstake posts and
use those. And the fdxing has to be firm enoguh to reset the forces from
the leaf springs.
-tony
5:21 p.m.
0) The book says that during self test:
- all keyboard indicators turn on and off
- the bell tone sounds
1) In my experience the problem is with (in order of likelihood):
- bad keyboard, unless the cable / connections are a repair
- bad connections : bent out of shape or oxidised
- cable defect
2) Four LEDS lit indicates a sad keyboard, I presume the 8051 sets the
LEDs on reset and clears them on receipt of self test traffic from the
main unit
+) I can't offer any comment on the self-test traffic to/from the
keyboard. Perhaps the place to start investigating, the signalling is
RS-423, especially with a known good unit for comparison. The technical
manual is on BitSavers.
HTH
Martin
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of Charles
Sent: 30 September 2008 18:21
To: cctalk at classiccmp.org
Subject: VT220 Keyboard Error 4?
I turned on my VT220 for the first time in nearly a year. The
screen says "VT220 Keyboard Error 4", all four green LED's (on the
top right of the keyboard) stay lit, and nothing appears on the
screen when I type.
Disconnecting and reconnecting the coiled-cord between the
keyboard and the terminal causes a cursor block to appear on the
screen, but the keyboard is still locked and the LEDs stay on.
Power-cycling the terminal shows the same error message.
However, the boot prompts from the 11/23+ are displayed normally,
so the receive part of the terminal at least is working.
Where should I start looking, before replacing the keyboard?
thanks for any hints
-Charles
5778
days inactive
5779
days old
5 comments
5 participants
participants (5)
-
ard＠p850ug1.demon.co.uk -
charlesmorris800＠centurytel.net -
mjd.bishop＠emeritus-solutions.com -
Paul_Koning＠Dell.com -
witchy＠binarydinosaurs.co.uk