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2-22
420 Series
2.8
Display and VGA Board Troubleshooting
This section describes how to determine if the 420 series display is functioning properly. Start
with Procedure 1 and continue with the other procedures as instructed.
Procedure 1:
Contrast Control Check (420CDS only)
Procedure 2:
External CRT Check
Procedure 3:
Diagnostic Test Program Execution Check
Procedure 4:
Connector Check
Procedure 5:
Replacement Check
Procedure 1
Contrast Control Check (420CDS only)
Contrast is changed by the contrast dial. If the contrast does not change when you turn the
contrast dial, perform Procedure 2.
Procedure 2
External CRT Check
Connect the external CRT to the 420 series external monitor port, then boot the computer.
The computer automatically detects the external CRT even if Resume mode is enabled.
If the external CRT works correctly, the internal LCD display may be damaged. Go to Proce-
dure 4.
If the external CRT appears to have the same problem as the internal LCD, the display con-
troller may be damaged. Go to Procedure 3.
Procedure 3
Diagnostic Test Program Execution Check
The Display Test program is stored on the 420 series Diagnostic Disk. This program checks
the display controller on the system board. After loading Toshiba MS-DOS, run the Diagnos-
tic Program. Refer to Chapter 3, Tests and Diagnostics, for details.
If an error is detected, go to Procedure 4. If an error is not detected, the display is function-
ing properly.