LG 20LS7D(C)-UB - Manual (Page 14)

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1. TV/CATV doesn't display
Check TU4002 Pin9(Video output)
Can you see the normal signal?
Could you measure voltage of
TU4002 & IIC lines?
Are they all normal?
You should replace TUNER.
You should check power line
& IIC lines.
Check the input(Pin63) of AV switch(IC5003).
Can you see the normal waveform? After checking the Power of AV switch you should
decide to replace AV switch or not.
Yes
Yes
No No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Check the output(Pin56) of AV switch(IC5003).
Can you see the normal waveform? After checking the Power of AV switch you should
decide to replace AV switch or not.
Check the input(Pin1) of LPF(IC4006).
Can you see the normal waveform? After checking the Power of LPF you should
decide to replace LPF or not.
Check the output(Pin8) of LPF(IC4006).
Can you see the normal waveform? After checking the Power of LPF you should
decide to replace LPF or not.
Check the input(PinH26) of BCM3550(IC4006).
Measure waveform at C1010 because it’s more
easy to check.
Can you see the normal waveform? This board has big problem because Main chip
(BCM3550) have some troubles.
After checking thoroughly all path once again,
You should decide to replace BCM3550 or not.
TROUBLESHOOTING