Keithley 2520, Service Manual, Page: 76 / 137

4-4 Troubleshooting Model 2520 Pulsed Laser Diode Test System Service Manual
4. Select DISPLAY-PATTERNS, and press ENTER to start the display test. There
are five parts to the display test. Each time a front panel key (except EXIT) is
pressed, the next part of the test sequence is selected. The five parts of the test
sequence are as follows:
• Checkerboard pattern (alternate pixels on) and all annunciators.
• Checkerboard pattern and the annunciators that are on during normal
operation.
• Horizontal lines (pixels) of the first digit are sequenced.
• Vertical lines (pixels) of the first digit are sequenced.
• Each digit (and adjacent annunciator) is sequenced. All the pixels of the
selected digit are on.
5. When finished, abort the display test by pressing EXIT. The instrument returns to
the FRONT PANEL TESTS MENU. Continue pressing EXIT to back out of the
menu structure.
CHAR SET test
The character set test lets you display all characters. Perform the following steps to run the
character set test:
1. Display the MAIN MENU by pressing the MENU key.
2. Select TEST, and press ENTER to display the SELF-TEST MENU.
3. Select DISPLAY-TESTS, and press ENTER to display the following menu:
FRONT PANEL TESTS
KEYS DISPLAY-PATTERNS CHAR-SET
4. Select CHAR-SET, and press ENTER to start the character set test. Press any key
except EXIT to cycle through all displayable characters.
5. When finished, abort the character set test by pressing EXIT. The instrument
returns to the FRONT PANEL TESTS MENU. Continue pressing EXIT to back
out of the menu structure.
Principles of operation
The following information is provided to support the troubleshooting tests and procedures
covered in this section of the manual. Refer to the following drawings:
Figure 4-1 — Overall block diagram
Figure 4-2 — Analog circuitry block diagram
Figure 4-3 — Power supply block diagram
Figure 4-4 — Digital circuitry block diagram