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
+) 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.
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