7 Jun
2020
7 Jun
'20
10:27 a.m.
Until a few minutes ago, my VT240 was operating normally, but now it's
unresponsive (fails during power-on self test).
Normal behavior was: display a checkerboard, then two different
intensity all-white bands growing slowly up from the bottom of the
screen, then a beep and the expected "VT240 Monitor Error 9" (because
I'm using an old B&W composite monitor instead of the DEC VR201 with
special cable). Thereafter, normal operation.
Now, it briefly displays the checkerboard (and all four keyboard lights
turn on, then off); then the Lock and Wait lights come on and nothing
else happens. Blank screen.
Power-OK light on the back is illuminated and 5.19 volts measured on the
board. Haven't checked +12 (or the internally derived keyboard +5) yet.
Another possibly useful observation: I can press the Setup (or any
other) key about four times and hear a keyclick sound each time. But
then it stops playing the click sound if I keep pressing keys. This
suggests that the interrupt on the CPU (a T11) is not being responded to.
The technical manual is very detailed but does not describe the
specifics of the POST, which could be useful in locating the failed
circuit (or firmware).
Can anyone with experience in debugging these terminals lend a hand?
Should I even be looking at the main board, or the keyboard which also
has an 8051 CPU??
thanks.
8 Jun
8 Jun
1:37 a.m.
On 07/06/2020 18:27, Charles via cctalk wrote:
Until a few minutes ago, my VT240 was operating
normally, but now it's
unresponsive (fails during power-on self test).
Normal behavior was: display a checkerboard, then two different
intensity all-white bands growing slowly up from the bottom of the
screen, then a beep and the expected "VT240 Monitor Error 9" (because
I'm using an old B&W composite monitor instead of the DEC VR201 with
special cable). Thereafter, normal operation.
Now, it briefly displays the checkerboard (and all four keyboard
lights turn on, then off); then the Lock and Wait lights come on and
nothing else happens. Blank screen.
The keyboard LEDs are used to indicate the test being performed, in this
case test 5 failed. They are listed in the pocket service guide. For the
first 6 codes it just says fatal error, replace terminal controller
board. I don't think it is the keyboard. You should get an error code 7
on screen for that.
I'm afraid I haven't looked into the VT240 firmware but I have looked at
the VT220 previously. Here are some of my notes on the self test:
0 = 8051 Internal RAM Test (Data=0xAA)
0 = 8051 Internal RAM Test (Data=0x55)
0 = 8051 Internal RAM Test (Data=0x00)
1 = 8051 Internal ROM Checksum (8840: lcall $8870)
2 = External ROM Checksum 0x8000 (884B: lcall $8870)
3 = External ROM Checksum 0xC000
8 = Screen RAM 0 (Addr=0xA000 Data=0xAA)
9 = Screen RAM 1 (Addr=0xA800 Data=0xAA)
A = Atrrib RAM 0 (Addr=0x8000 Data=0xAA)
B = Attrib RAM 1 (Addr=0x8800 Data=0xAA)
8 = Screen RAM 0 (Addr=0xA000 Data=0x55)
9 = Screen RAM 1 (Addr=0xA800 Data=0x55)
A = Atrrib RAM 0 (Addr=0x8000 Data=0x55)
B = Attrib RAM 1 (Addr=0x8800 Data=0x55)
8 = Screen RAM 0 (Addr=0xA000 Data=??)
9 = Screen RAM 1 (Addr=0xA800 Data=??)
A = Atrrib RAM 0 (Addr=0x8000 Data=??)
B = Attrib RAM 1 (Addr=0x8800 Data=??)
C = Character ROM (read only)
D = Alt Character RAM (read/write)
E = Alt Character RAM (?)
I know the VT240 uses a different processor to the VT220 but this gives
you an idea of the sort of things that are being tested early on. I
imagine the VT240 will carry out a similar set of tests.
Matt
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charlesmorris800＠centurytel.net -
matt＠9track.net