Philips PTV800, Руководство по обслуживанию

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1. Tune to a weak station, or loosely couple the antenna to observe a snowy picture.
2. Set the R.F. AGC Delay (R256) to its fully counter- clockwise (CCW) position.
3. Slowly advance R256 clockwise (CW) to a point slightly beyond the point of minimum
snow.
Note: Do not advance the control any further as it may result in an overloaded picture on the
face of the CRT (caused by a strong signal from local station). The range of the AGC voltage
supplied to Pin 9 (see TP3) of the Varactor Tuner will vary from approximately 4.2Vdc (Without
Signal) to about 1.87Vdc (RF Signal of 10mV).
VCO & AFT Adjustment
Single Tuner Models (ASG051 and 52)
1. Cut the shield break points around IC200 and the IF Circuitry (see zone K-2). Peel the
top cover of the shield to gain access to the internal circuitry.
2. Short Test Points 16A & 16B off the Varactor Tuner Module (see zone J-1, bottom
view).
3. Short Test Point 23 (Pin 13 of IC200) to ground (Shield around IC200 is good).
4. Connect a DC Voltmeter to Test Point 7 (Pin 18 of IC200).
5. Turn the set on and record the voltage reading from Test Point 7 (typically 4.5 to
5.0Vdc).
6. Turn off the set and remove both shorts from Test Points TP16A/B and TP23.
7. Connect the Coincidence line at the collector of Q207 (jumpTP47, zone J-6, on top of
board) to +5Vdc line on the tuner.
8. Apply a local broadcast signal (air signal) to the antenna terminals and turn the set on.
9. Select the Cable Tuning from the menu system. Select channel 36 or some other high
band inactive cable channel.
10. While still in the cable mode, select your local VHF broadcast channel. The Tuning
System will attempt to tune three times and then lock on to the FCC assigned
frequency.
11. Adjust the AFT Coil (L202) to obtain a reading of +7.1Vdc (+/-25mVdc) at Test Point
TP2.
12. Adjust the VCO Coil (L204) to obtain the same DC voltage reading at Test Point TP7
that was noted in step 5 of this adjustment procedure.
13. Remove the jumper from the Coincidence line.
14. Verify this adjustment by changing between the high band (inactive cable channel) and
your local VHF broadcast channel (ensure that the local broadcast channels lock in
quickly).