LG CM9750 Service Manual

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3-5

ONE POINT REPAIR GUIDE

4. VFD IS NOT DISPLAYED WHEN POWER ON THE SET

When power on the set, any icons or characters on VFD are not displayed.

4-1. VFD (VFD301)

4-1-1. Solution

Please check and replace VFD301 on FRONT board.

4-1-2. How to troubleshoot (Countermeasure)

1) Check if 39 V, FL+ and FL- are output from SMPS to VFD via the MAIN board.

2) Check if the IC501 outputs VFD_RST, VFD_CLK, VFD_DO, and VFD_STB to the FRONT board.

3) Check if the VFD grid current amplifier circuit on the FRONT board.

Check the drive signal to the transistor’s base.

 If the control signals from VFD (DGND_2, VH, VDD) isn’t output, replace VFD with a new one.

4-1-3. Service hint (Any picture / Remark)

R327(TP 304)

Q301 Emitter

about

30 Vp-p

< FRONT circuit > < Waveform of the grid current driver>

CN315

VFD_STB,

VFD_CLK,

VFD_DO

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General

Type	-
Cassette deck	No
Product color	Black
Number of decks	1 deck(s)
Disc loading type	Tray
Optical disc player	Yes
Number of optical discs	1 discs
Speaker type	3-way
RMS rated power	- W
Woofer diameter	304.8 mm
Tweeter diameter	25.4 mm
Number of speakers	2
Mid-range driver diameter	165.1 mm
Subwoofer driver diameter (imperial)	12 \
Tuner type	Digital
FM band range	87.5 - 108 MHz
Supported radio bands	FM
Headphone connectivity	3.5 mm
USB 2.0 ports quantity	USB 2.0 ports have a data transmission speed of 480 Mbps, and are backwards compatible with USB 1.1 ports. You can connect all kinds of peripheral devices to them.
Microphone connectivity	6.3 mm
Apple docking compatibility	Not supported
Disc types supported	CD, CD-R, CD-RW
Playback disc formats	CD audio
Audio formats supported	MP3, WMA
Volume control	Rotary
Equalizer modes	Bass, Classic, Jazz, Pop, Rock
Power source	AC