Printer Port Loopback Test (6-Pin); Screen Alignment Test - DEC VT420 Service Manual

18 Troubleshooting and Testing

2.2.7 Printer Port Loopback Test (6-Pin)

For this test, you connect the printer 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 the following sequences:
ESC [ 4 ; 3 y
ESC [ 4 ; 3 ; 9 y
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 message appears on the screen.
VT420 OK
If the test finds an error:
The screen displays the following message. See Table 2–3.
VT420 DEC-423 Port Error -- 6

2.2.8 Screen Alignment Test

This test fills the screen with uppercase E's. Use this display to adjust
the display height, width, and linearity. See Chapter 4 for the adjustment
procedures.
Runs the test once.
Runs the test continuously.