14 Troubleshooting and Testing
If the test finds an error:
If possible, the terminal displays an error message at the upper-left corner
of the screen. Each error message starts on a new line at the left margin
of the display. Table 2–3 describes these error messages.
The error messages disappear when the terminal receives any character
(except XON) or when you type any key. In local mode, the terminal
ignores characters from the host, so error messages are not affected.
2.2.4 DEC-423 Port Loopback Test (6-Pin)
For this test, connect the DEC-423 port transmit and receive data lines
together with a loopback connector (Figure 2–2). The terminal sends a
predefined set of characters on its transmit line and receives them on
its receive line. Then the terminal compares the output characters to the
input characters. If the characters do no match, an error message appears
on the screen.
To run the test:
Use a DEC-423 loopback connector, PN 12-25083-01.
1. Set up the terminal (Sections 2.2.1 and 2.2.2).
2. Connect the loopback connector to the 6-pin DEC-423 port.
3. Type one of the following sequences:
ESC [ 4 ; 7 y
ESC [ 4 ; 7 ; 9 y
Runs the test once.
Runs the test continuously.
NOTE
The continuously running test ends only if an error occurs or you
turn off the terminal. The keyboard does not make a bell tone
during this test.
If the test is successful:
1. The keyboard makes a bell tone.
2. The keyboard’s LED indicators are off.
3. A VT420 OK message appears on the screen.
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