Focus Problems - HP 8560A Service Manual

3. Perform the Display Adjustment in Chapter 2. Isolate the problem to either the X or Y
axis by noting the behavior of the adjustments. If the line generator or fast zero-span
portion of the adjustment fails, troubleshoot the A2 assembly.
4. If the adjustments do not remedy the problem, set the HP 8560A's (LINE) switch off and
place the Al7 CRT Driver in the service position.
5. Distortion confined to one axis (vertical or horizontal only), indicates a faulty Al7
assembly's X or Y Deflection Amplifier. Use the alternate good deflection amplifier for
obtaining typical voltages. (There is enough symmetry in a typical display that the
voltages should be similar between these circuits.)
6. Monitor the waveforms at A17TPll and A17TP14 (or TP12 and TP13). The 50 to
100 Vp-p ac component of the waveforms at the X and X' (or Y and Y') outputs should
be mirror images of each other. The dc average should be 55 V.
7. The appropriate POSN adjustment (A17R57 or A17R77) should change the dc component
of both X and X' (or Y and Y') outputs in opposite directions.
8. The appropriate GAIN adjustment (A17R55 or A17R75) should change the ac component
in both outputs by the same amount.
9. If the display is a single dot, check the base of A17Q18 for -10.3 V +/-0.3.V. Verify the
signals at TPll, TP14, TP12, and TP13.
10. If signals are correct and cables to CRT are good, suspect the CRT.

Focus Problems

Focus problems may be due to a defective A18Vl CRT, improper adjustments, improper
connections, or absence of high voltage. The A2 Controller's focus-control circuitry has a very
minor effect on the overall focus.
Although A17's Grid Level Shifter (function block D) is the leading cause of Al7 focus.
problems, function blocks C, E, F, and H generally have less effect on focus, but may cause
poor focus that is a function of screen position, length of line, or intensity.
1. Connect a DVM's positive lead to A25202, pin 2. Connect the negative lead to A2J202
pin 6.
2. Use the knob to change the focus value from 0 to 255.
3. If the DVM reads near 0 Vdc with the focus set to 0, and near -10 Vdc with the focus set
to 255, A2's focus control circuitry is working properly.
4. Perform the Display Adjustment in Chapter 2. Note that A17R34 COURSE FOCUS has
the greatest effect on focus. Adjustment A17R93 ASTIG and A17R92 DDD have a lesser
effect, and A17R21 Z FOCUS, A17R26 X FOCUS and front-panel adjustment (press
5. If the focus of some areas of the screen are worse than normal, continue with step 11. If
no part of the screen can be brought to sharp focus, continue with step 6. (CRTs have
some normal focus variation across their face.)
12-8 Display/Power Supply Section
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