HP 85662A, Troubleshooting And Repair Manual

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Display Troubleshooting
The Display system consists of four sections:
Input Section Analog-Digital Converter and Track and Hold
Processor Section Memory, Data Manipulator, Main Control,
and Interface
CRT Driver Section Trigger, Intensity Control, and Line
Generator.
CRT Amplifier Section
High Voltage Regulator and either XYZ Driver
Amplifier (Serial Prefixes 3004A and above) or Z Axis
Amplifier X Deflection Amplifier and Y Deflection
Amplifier
Isolation of a malfunction to one of the above sections is done with the use of rear-panel
display outputs and the internal test programs.
If the left INSTR CHECK LED is on, a failure has probably occurred in Digital Storage.
Refer to the A3 Digital Storage Troubleshooting notes for the correct troubleshooting
procedure.
The following paragraphs briefly describe the failure modes and appropriate places to begin
the troubleshooting.
Characters Only
If only the characters on the CRT display are affected, the problem most likely exists on the
Memory.
Graticule and Characters Only
If the graticule and characters are incorrect, but the video information appears to be correct,
suspect the System ROMs on first. Also the “long POP” test of the RF Section
memory should be performed. Refer to the Digital Storage Troubleshooting notes for more
information.
Al 1