Zenith ZVM-133-TC Service Manual page 30

e. If it is not, check for pulses at the following loca-
tions and in the order shown. If pulses are not
present, replace the logic board or troubleshoot
the components in parentheses. Pin 35 of
IC101 (IC101), Pin 8 of IC105 (IC102, IC105,
C107, C108, R123), and pin 12 of IC104
(IC104).
f. Check for continuity of R124 and CR109 to
make sure that they are functional.
If all these checks are satisfactory and CR109
is still not flashing, the problem may be in the
reset circuit.
g. Test the reset circuit by momentarily grounding
TP3 and then connecting it to the
+
5 VDC sup-
ply (See Figure 4-23). If this causes CR109 to
flash, troubleshoot the components associated
with Q1 07, the reset transistor.
12. If CR109 is flashing but the monitor fails to re-
spond when you touch the screen, connect an os-
cilloscope to L101 (either end) and look for
waveform G in Figure 4-24 (See Figure 4-24 for
oscilloscope settings).
13. If waveform G is not correct, test IC102 pins 2
and 3. This gate inverts the input signal. Replace
IC102 if necessary.
14. If waveform G is correct, keep the oscilloscope
on L 101 and connect another oscilloscope chan-
nel to L 102 (either end). Look for waveform G and
F of Figure 4-24 (See Figure 4-24 for oscilloscope
settings).
15. If waveforms G and F are not correct, test IC102
pins 4, 5, and 6. This gate inverts the input signal
(pin 4) at the output (pin 6). Pin 5 adds drive to
the circuit and it should be "high." Replace IC102
if necessary.
Page 4-12
16. If waveforms G and F are correct, keep the oscillo-
scope connected to L 101 and connect the other
channel to the junction of R101, R106, and pin
9 of IC201 (Point E on the schematic). Look for
Z and E waveforms of Figure 4-24 (See Figure
4-24 Z and E for oscilloscope settings).
17. If waveforms Z and E are not correct, test IC104
pins 3 to 6 and 8 to 11. IC104 buffers and inverts
the input signals. Replace IC104 if necessary.
18. If waveforms Z and E are correct, proceed to step
19. If the preceding has caused CR109 to start
flashing, the problem is in Q701 or one of its as-
sociated circuit components.
19. If CR109 is flashing but the monitor still fails to
respond when you touch the screen, connect an
oscilloscope and attempt to display waveforms B
and A as shown in Figure 4-24.
If pulses are not observed, replace the logic board
or IC104, IC106, IC108, and IC109.
20. Check the horizontal and vertical collector plates
as follows:
a. Set the oscilloscope to 100 mV/Div AC.
b. Turn the logic board sensitivity (R204) fully
counterclockwise. This is a maximum gain and
it should cause an increase in noise amplitude
(see Figures 4-2 and 4-23).
c. Place a lit incandescent light bulb (40 to 100
watts) several inches from the top left corner
of the face of the CRT to induce a 60 Hz Signal
into the horizontal circuit from the infrared out-
put of the bulb.
If the horizontal collector assembly is good, the
oscilloscope will display a 60 Hz sine wave.
Servicing