Input Level Adjustment; Focus Adjustment; Purity And Convergence Adjustments - Sanyo HT28745 Service Manual

HIGH VOLTAGE HOLD-DOWN TEST
Every time the receiver is serviced, the HIGH VOLTAGE
HOLD-DOWN circuit must be tested for proper operation by
following these steps:
1. Connect receiver to 120V AC line. Tune receiver to active
channel. Reset the picture controls to the Sports level.
2. Check that the voltage measured between TP7 and TE7
(ground side) on the P/D PC board is within 20 VDC to 24
VDC. If the voltage is out of this range, the Hold-Down
Circuit must be checked.
3. Connect a DC Voltage supply to TP7 and TE7 through a
100 ohm 1/4W resistor. Adjust the DC voltage to 26 VDC.
The receiver should shut down, losing raster and sound.
Then the receiver should turn off automatically.
This reaction indicates that the Hold-Down circuit is func-
tioning properly. If the receiver does not shutdown, a
malfunction is indicated and its cause must be found and
corrected.
4. To obtain picture again, remove the DC Supply and wait
a few minutes. Now turn on the receiver.
HIGH VOLTAGE CHECK
Note: +B (+140V) Voltage Check and Grayscale Adjustment
must be completed before attempting High Voltage
Check.
1. Connect high voltage voltmeter – lead to ground, and
connect + lead to anode of picture tube.
2. Tune receiver to an active channel and confirm TV is
operating properly.
3. Eliminate the beam current by adjusting the contrast and
brightness controls to minimum.
4. Confirm high voltage is within 28.1 KV and 32.0 KV. If
reading is not within range, check horizontal circuit.
No high-voltage adjustment is provided on this chassis.

FOCUS ADJUSTMENT

Adjust focus control (T402) for well defined scanning lines.

PURITY AND CONVERGENCE ADJUSTMENTS

Purity and Convergence have been aligned at the factory.
No re-alignment is necessary.
SERVICE ADJUSTMENTS (Continued)
MULTI-SOUND SECTION ADJUSTMENTS
Note: Multi-Sound Section must be adjusted after
A101 (U/V Tuner), IC3601 (MTS Decoder), Digital
Module or IC802 (EEPROM) is replaced.

INPUT LEVEL ADJUSTMENT

1. Connect a signal to the analog antenna terminal with
audio of 1 KH
Z
2. Turn off the receiver and disconnect the AC power cord
(AC 120V line).
3. Connect voltmeter (RMS) to TP317 and ground on the
Main PC board.
4. While pressing the VOLUME – key, reconnect the AC
power cord. The Service Menu will now appear.
5. Select NO. 080 (ATT: MTS Input Level) with the
L or M key.
6. Adjust the + or – key for a voltmeter reading of 400 ±
20 mVrms at TP317.
SEPARATION ADJUSTMENT
7. Turn off the receiver and disconnect the AC power cord
(AC 120V line).
8. Connect oscilloscope CH1 to TP317 and CH2 to TP318
and ground.
9. Connect an MTS TV/Stereo generator to antenna terminal.
10. While pressing the VOLUME – key, reconnect the AC
power cord. The Service Menu will now appear.
11. Select pilot, 300Hz audio frequency and Left modulating
signal.
12. Select NO. 081 (WDB: Wide Band) with the L or M key.
13. Adjust the + or – key for minimum low frequencies at
TP317. (See Figure 7.)
14. Select 4 KHz audio frequency and Right modulating signal.
15. Select NO. 082 (SPC: Spectral) with the L or M key.
16. Adjust the + or – key for minimum high frequencies at
TP318. (See Figure 7.)
Repeat adjustments (steps 11–16) until no further decreases
in amplitude can be obtained. Press the MENU key to turn
off the Service Menu display.
TP317 (R)
TP318 (L)
Figure 7. Separation Adjustments
— 16 —
100% modulation.
Minimize L leakage
300Hz
Minimize R leakage
4KHz