PHILIPS; PTV800_PTV805_PTV810_PTV811_PTV815_PTV820_PTV825 _ SERVICE ADJUSTMENTS.
PART -1
- All service adjustment to this chassis are hot voltage wise, So ensure the use of properly insulated tools.
TUNER ADJUSTMENT
- Turn the set ON, and tune to an on-air station.
- Connect digital voltmeter to [TP-41] on the small signal panel.
- Adjust (C341) [Zone E-6] to obtain a reading of 2.5VDC on the meter.
- This adjustment may effect on-screen menu positioning as well as other graphics generated set.
RF AGC DELAY
- Single tuner models. [ASG051 & ASG052]. The adjustment control [R202] can be located on the small signal panel in zone area J2.
- Tune to a weak station.
- Set R202 to its fully counterclockwise position.
- Slowly advance it to a point slightly beyond the point of minimum noise in picture.
- Two tuner models. [ASG053 & ASG054]. Control resistor [R256] can be located on the small signal panel zone area K5 Use the adjustment procedure as described above, to this adjustment too.
- Do not advance the control any further, as it may result in an overloaded picture. The range of the AGC voltage supplied to pin [9] of the Varactor tuner may vary from 4.2VDC without signal, and 1.87VDC with signal.
VCO AND AFT ADJUSTMENT.
Single tuner models.
- Cut the shield break point around IC200, and the IF circuitry. Peel the top cover of the shield to gain access to internal circuitry.
- Short test points 16A&16B of the varactor tuner module.
- Short test point [23] to ground.
- Connect DC voltmeter to test point [7].
- Turn the set ON, and record the voltage reading from test point [7]. Typically 4.5V to 5.0VDC.
- Turn OFF the set, and remove both shorts from test points TP16A/B and TP23.
- Connect the coincidence line at the collector of [Q207] to +5V DC line on the tuner.
- Apply local broadcast signal, preferably on-air signal, to antenna terminals and turn the set ON.
- Select the cable tuning from the menu item, select channel 36 or other high band inactive cable channel.
- While still in cable mode, select local VHF broadcast channel. The tuning system will attempt to tune three times and then lock on to the FCC assigned frequency.
- Adjust AFT coil [L202] to obtain a reading of +7.5VDC at test point [tp2].
- Adjust VCO coil [L204] to obtain the same DC voltage that was noted above.
- Remove the jumper wire from coincidence line.
- Verify the adjustment by changing between by High Band and local VHF broadcast channel, and ensure that the local broadcast channels lock in quickly.
Two tuner models.
- Cut the shield break points around IC201 and IF circuitry. Peel back the top cover of the shield to gain access to the internal circuitry.
- Short test points [16C&D] of the varactor tuner module .
- Short test point [23A], pin 13 of IC201, to ground..
- Connect DC voltmeter to test point [7A].
- Turn the set ON and record the voltage reading from test point [7A]; typically 4.5 to 5.0VDC.
- Turn OFF the set and remove shorts from test points [TP16C,D&23A].
- Connect the coincidence line at the collector of Q207, to 5VDC line on the tuner.
- Apply local broadcast signal by the antenna terminal, and turn ON the set.
- Select the Cable Tuning from menu options,and select channes 36 or some other high band inactive cable channel.
- While still in cable mode, select local VHF broadcast channel. The tuning system will attempt to tune three times, and then lock on to the FCC assigned frequency.
- Adjust the AFT coil [L219] to obtain a reading of +6.6VDC, at test point [TP2A].
- Adjust the VCO coil [L220] to obtain the same DC voltage reading at test point [TP7A] that was noted in step 5 of this adjustment procedure.
- Remove the jumper from the coincidence line.
- Verify this adjustment by changing between the high-band and local VHF broadcast channel and ensure that local broadcast channels locks in quickly.
Continued in part-2
