6-101
5. Check the following signals: 2XH at U314 pin 4, 2XH at U308A pin 9, HORIZCLK at U220B
pin 12, HCLK at U220B pin 13, DLY'D HCLK at U220A pin 1 (held LO when the PLL is unlocked),
VERTSYNC at U310A pin 1. Troubleshoot the cause of any missing Signals. (See Figure 3-14 in
Section 3 for typical waveforms.)
4. Check U308B pin 3 for a LO pulse coincident with the Horizontal Sync of the applied video signal.
If not present, check for the presence of the COMPSYNC signal at U310A pin 5 (waveform 169). If
COMPSYNC is ok, but the signal at U308B pin 3 is not, troubleshoot U420 and associated cir-
cuitry. If both are missing, troubleshoot back through the Video Option input and signal processing
circuitry to find the problem.
3. Check 0330, CR324, CR326, CR325, and VR234 for opens or shorts.
2. Check pin 13 of U314 for narrow positive pulses that coincide with the horizontal sync pulses of
the applied video signal. If not present, suspect the Phase Locked Loop circuitry and its input and
output signals.
1. Set the Trigger CPLG to TV, Trigger SOURCE to CH 2, Trigger SLOPE to - (neg-sync), A TV
COUPLING to FIELD1-Line count to 10, CH 2 input coupling to DC, SEC/DIV to 200
ILS ,
TV
CLAMP OFF, and VOLTS/DIV to 1 V (for a two-division signal amplitude). Connect a negative
sync composite video signal to the CH 2 input.
PHASE-LOCKED
LOOP PROBLEM
6. Set Input Coupling to GND and check that U510 pin 6 is within 1 V of ground level. If not, trouble-
shoot U510 and associated circuitry.
5. Set the Input Coupling to DC and check that the negative sync tip amplitude at U610 pin 9 is
about 50 to 75 mV (from back-porch level to negative tip) with about a -3 V dc offset. If yes, the
AGC amplifier and Sync Tip Clamp circuit are ok. Troubleshoot the Fixed Gain Amplifier, the Sync
Pickoff Comparator, the Trigger Back-Porch Clamp, and associated circuitry. If the signal is not
correct at pin 9 of U610 with the correct TVRC signal applied, troubleshoot the AGC amplifier and
Sync Tip Clamp, and associated feedback circuitry.
4. Set the Input Coupling on the 2430 to GND and check that the de levels at U612 pins 3 and 13
are about the same. If not, troubleshoot U710B and associated circuitry.
3. Is the TVRC signal present at U612 pin 3 (waveform 159)? If not, troubleshoot the source of the
TVRC signal (0140 and U150) and the connecting signal path.
2. Check that U750 pin 16 (schematic diagram 20) is LO with negative sync selected and HI with
positive sync selected. If not, troubleshoot U750.
1. Check U610 pin 5 for a horizontal line sync signal having the negative sync tip at about 0.5 V and
a back-porch level of +4.5 V. If correct, check pin 6 of U420B for the correct signal (see
waveform 162). If not correct there, troubleshoot the Sync Pickoff Comparator (0504 and 0510)
and Pulse Stretcher circuits.
See INITIAL SETUP in TV Trigger Problem for control settings and signal application. Set the test
scope Sec/Div setting to 5
ILS
and the Volts/Div to 2 V.
SIGNAL
PROCESSING
PROBLEM
Table 6-7 (cont)
Maintenance-2430 Service
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