Printer; Keyboard; Display Interface Module (Dim); 98760A Standard Color Graphics Display - HP 9020 Service Manual

Testing and Troubleshooting
3-7
Printer
The printer self-test is initiated by powerup or by a SCRATCH ALL or LOAD BIN. This test shifts
serial data through the shift register on the printhead chip modules and reads the output data,
checks the value of each printhead resistor, checksums the program and character ROMs, and tests
printer RAM. The printer checks each resistor for the proper resistance range and adjusts the burn
time for each head dependent upon an average resistance of that head. If any resistors are out of
specification, an error message is issued. Also, the printer logic board monitors the motor drive
board, the head voltage, and the temperature of the printhead.
The printhead control lines are constantly monitored to prevent a sticking condition from destroying
a printhead. In the case of a failure, the head voltage is shut down and the printer's status register
reports the failure to the operating system. An LED on the printer's logic board also lights when a
failure occurs. The LED is visible through the air vents under the keyboard.
Pressing the form feed and paper advance switches at the same time produces a printer output.
This provides a quick confidence test of the printer, checking for missing dots and overall print
quality.
Keyboard
The keyboard processor turns the
CAPS
LED on and off and turns the
PRINT ALL
LED on at
power-up. This test indicates that the processor is capable of executing code. When the BASIC
operating system begins to run, it turns the
PRINT ALL
LED off and turns the
CAPS
LED back on.
When HP-UX runs, both the
PRINT ALL
and and
CAPS
LEOs are off. With an operating system
installed, pressing (CAPS) and checking the toggling of the LED verifies keyboard operation.
Successful keyboard operation means that the keyboard processor and scanning circuits are
working. The self-test supervisory code tests the keyboard
110
later in the power-up sequence.
Display Interface Module (DIM)
The display interface module (DIM) contains self-teSting hardware which either verifies a greater
than 95% confidence in the assembly or indicates a fault. The test hardware outputs a test pattern
to the display. The test is initiated by pressing the self-test button underneath the display or by
program request. The self-test supervisory code, described below, tests the display buffer memory
of DIM.
98760A Standard Color Graphics Display
The green SWEEP INDICATOR LED lights at powerup to indicate that the vertical and horizontal
scans are operating correctly. High voltage is enabled by proper scan functioning. The LED remains
on as long as there is no scan fault condition. If the LED fails to light at powerup, a faulty scan is
indicated.
98770A High Performance Color Graphics Display
The display contains its own power supply and can be tested when disconnected from the compu-
ter. A self-test connector and switch assembly enable the testing. The DIM must be removed for
offline testing of the display. Offline testing is described in the 98770A Service Manual. Further
testing must be done by the DIM or by the system integrity tests.