636 Chapter12
Display/Power Supply Section
Intensity Problems
Intensity Problems
Intensity problems, or absence of display, can be due to the A17
assembly intensity amplifier (function block A), intensity grid level
shifter (function block B), CRT (A18V1), interconnections, or lack of
proper supplies or inputs to A17.
1. On the HP 8560E spectrum analyzer, press
DISPLAY and INTENSITY.
2. Rotate the front panel knob (RPG), and check that the intensity
changes from dim, but readable, to bright.
3. If the intensity function does not function properly, troubleshoot the
A2 controller assembly.
4. Perform the preliminary and Z-axis portions of the "Display
Adjustment" in Chapter 2. Verify that A17R11 CUTOFF functions
properly. If A17R11 CUTOFF does not function properly, place the
A17 CRT driver in the service position.
5. Verify that blanking pulses are present at A17TP2 using an
oscilloscope. The pulses should be normal TTL levels, approximately
1 µs wide and 4 or 7 µs apart. If the blanking pulses are not correct,
check the BLANKING output of the A2 controller assembly and
cable W7.
6. If blanking pulses are present, check A17TP10 with the oscilloscope.
The TP10 signal should vary with the front panel intensity
adjustment, and be approximately 55 Vp-p maximum. The signal
will be composed of both blanking pulses and varying intensity
levels for the lines being drawn.
• If a proper signal is not present at A17TP10, check A17Q1, Q2,
CR1, and CR2.
• If the TP10 signal does not vary with the front panel intensity
adjustment, check the signals at A17TP4 and A17TP1. Both
signals should vary with the front panel intensity adjustment.
The TP4 signal should be up to 4 Vp-p, and the TP1 signal should
be up to approximately 12 Vp-p.
WARNING The A17 CRT Driver contains lethal voltages with lethal
currents. Use extreme care when servicing this assembly.
Always disconnect the power cord from the instrument before
servicing this assembly. Failure to follow this precaution can
present a shock hazard which may result in personal injury.
NOTE The following measurements should be made with a high-voltage probe,
such as the HP 34111A. When using the high-voltage probe, connect the
ground lead securely to the HP 8560E chassis.
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