Philips LC4.8A Service Manual page 22

EN 22 5. LC4.8A AA
5.7.3 Tuner and IF
No Picture in RF Mode, but there is a Noise Raster
1. Check whether picture is present in AV. If not, go to Video
processing troubleshooting section.
2. If present, check if the Option settings are correct.
3. Check if all the supply voltages are present (3.3/5/8/12/33
V).
2
4. Check if the I C lines are working correctly (3.3 V).
5. Manually store a known channel and check if there is IF
output at Tuner pin 11.
6. Check the tuning DC voltage at pin 2 of the Tuner. The DC
voltage should vary according to the frequency/channel
being chosen.
7. If the tuning voltage is OK, check the tuner output, pin 11.
8. If it has no output, the Tuner may have a defect. Change
the Tuner.
Sound in Picture Problem for L' System (rolling horizontal
lines)
1. Check whether AGC L' in SAM mode is set to 0.
2. If yes, align the set to correct value.
Required System is not Selected Correctly
Check whether a Service jumper (#4204 & 4205, 0805 size) is
present. If yes, remove it.
5.7.4 Video Processing
No Power
1. Check +12 V and 3V3 at position 1J02.
2. If no supply, check the connector 1J02.
3. If it is correct, check the power supply board.
Power Supply is Correct, but no Green LED
1. Check if the connectors 1K00 are properly inserted.
2. If they are inserted correctly, check if the 3V3 is present.
No Picture Display (blank screen with correct sound
output)
1. Check whether the user menu is visible.
2. If the user menu is OK, activate teletext mode.
3. If teletext is OK, the problem is in the ADC (B18) &
Columbus 3D combfilter (B19), if present (depending on
model, see also paragraph "Teletext Path" in chapter 9).
4. If the user menu is not visible, check if the LCD panel
backlight is ON.
5. If the backlight is OFF, the problem is in the power supply
board or LCD panel. Also check pin 12 (LAMP_ON_OFF)
of 1J02. It should be HIGH during normal operation.
Note: For faultfinding purposes, it is important to know the
following: in Pixel Plus and Digital Crystal Clear models, which
have an ADC (B18) and Columbus 3D combfilter (B19), the
digital input of the scaler is used for the digital video path
(Hercules output), whereas the analogue RGB input (analogue
input of the scaler) is only used for teletext. This means that no
mixed mode (video plus teletext simultaneously) is possible. If
there is sound and teletext, but no video and user menu (blank
screen), the digital path (Hercules - ADC - Columbus - Scaler)
is faulty. If there is sound but no teletext, the back-end part
(Scaler - LCD panel) is faulty. In Crystal Clear models, which
do not have an ADC and Columbus, the RGB path (analogue
input of scaler) is used for both video and teletext.
No TV, but PC is Present
1. Check if Hsync_SDTV and Vsync_SDTV are present at pin
1 & pin13 of 7E03.
2. If they are present, check teletext output.
3. If there is no teletext output, the IC TDA150xx may be
defect.
Service Modes, Error Codes, and Fault Finding
5.7.5 Power Supply
In case the power supply does not work, check (apart from the
obvious fuse-check) if the oscillators in IC7001 (in TV sets with
37 inch screens) or in IC7001 and IC7U01 (in TV sets with 42
inch screens) are working. If not, replace the ICs.