BenQ TL650 Service Manual page 74

RS232 link fail
Check U28 pin20 is high?
Yes
Check U9 pin19 is high?
Yes
Check J12 pin RX and TX
is normal ?
Yes
Check signal U100 MCU_RX and
MCU_TX is normal
1. Check control pin RS232_TXEN status
No
(default high)
2. Check R629 or R630 is mounted?
Check L9 is mounted?
No
1. Check RS232 cable (pin2/pin3 is cross type
or normal type)
No
2. Cross type must plug in to substratum of J12
3. Normal type must plug in to upper stratum of
J12
Check U100 soldering or to change a new chip
No
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