Chapter 4 249
Troubleshooting the Analyzer
Troubleshooting the A16 Processor/Video Board Assembly
Troubleshooting the A16 Processor/Video
Board Assembly
After you have determined that the problem is caused by the A16
processor/video assembly, use the following procedures. The 8590 Series
Analyzers Component-Level Repair Service Guide is required to assist
with these procedures. Refer to Chapter 13 for a list of available
component-level service information.
If a signal cannot be displayed
If a signal cannot be displayed, and it has been determined that a
top-screen signal of two volts is present at VIDEO_IF, the problem may
be on the A16 processor/video board assembly.
1. Put 0 V into the video circuit, simulating a bottom-screen signal
level condition by setting the diagnostic to the ground reference
detector. Refer to “Verify the ground reference detector” located in
this chapter.
Use an oscilloscope to check for the following conditions. Refer to
Sheet 2 of 4 of the A16 processor/video board assembly
component-level information.
• Check for 0 V throughout the signal path through U201, U61,
U45, and U46.
• Check the offset by measuring the inverting and noninverting
pins on U201, U61, U45, and U46. The difference between both
measured values should not exceed 5 mV.
2. Replace any components with excess offset voltage.
3. Put 2 V into the video circuit, simulating a top-screen signal level
condition by setting the diagnostic to the 2 V reference detector.
Refer to “Verify the 2 V reference detector” located in this chapter.
Use an oscilloscope to check for the following conditions. Refer to
Sheet 2 of 4 of the A16 processor/video board assembly
component-level information.
• Check for 2 V throughout the signal path through U201, U61,
U45, and U46.
• Check the offset by measuring the inverting and noninverting
pins on U201, U61, U45, and U46. The difference between both
measured values should not exceed 5 mV.
4. Replace any components with excess offset voltage.
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