HP 8560A

6. If blanking pulses are present, check A17TPlO with the oscilloscope. The TPlO signal
should vary with the front-panel INTEN 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.
a. If a proper signal is not present at A17TP10, check A17Q1, Q2, CRl, and CR2.
b. If the blanking pulses do not reach 40 Vp-p with maximum intensity, turn off the
HP 8560A and check A17CRlO with an ohmmeter.
c. If the TPlO signal does not vary with the front-panel INTEN adjustment, check the
signals at A17TP4 and A17TPl. Both signals should vary with front panel INTEN
adjustment. The TP4 signal should be up to 4 Vp-p, and TPl signal should be up to
approximately 12 Vp-p.
Warning
The Al7 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 8560A chassis.
7. Carefully measure the grid voltage at A17J7 pin 6, and the cathode voltage at A17J7 pin
4. The display will work with a cathode voltage of -2450 V f250 V, provided the grid
voltage (A17J7 pin 6) is 30 to 100 V more negative than the cathode. A17Rl1, CUTOFF,
should be able to adjust the voltage difference over a 60 V range to account for tube
variations, and achieve proper intensity.
8. If the grid and cathode voltages are correct, turn off the HP 8560A and check A17CRlO
with an ohmmeter. If A17CRlO is good, suspect the A18Vl CRT.
9. If the grid and cathode voltages are too low, turn off the power and disconnect W8 from
the base of A18Vl CRT, and recheck the grid and cathode voltages.
10. If the grid and cathode voltages are still too low, refer to “CRT Supply” in this chapter
and the High-Voltage Power Supply Adjustment procedure.
11. If voltages are correct when the tube is disconnected, the CRT is probably defective.
Caution
The pins on the A18Vl CRT bend easily. Be careful not to bend pins when
connecting W8 to A18VI.
12- 10 Display/Power Supply Section