ViewSonic VA702B Service Manual - Page 41

Backlight can't be turned

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5. Backlight can't be turned on No raster? Yes LED Green? Yes Backlight cannot be turned on. Yes Is there 14Vdc voltage on pin13 of IC501? No Check power supply Yes Is there high-level voltage on pin8 of IC501? Yes Check CN501, CN502, CN503 and CN504? Yes No Is R526 Ok? No No Yes Check I/F board R526 open Connecting the output connector again Is there pulse waveform on No pin1, pin3, pin15 and pin16 of IC501 at the moment of restart? Yes No Is ok T501, T502? Is Ok IC501? No Yes Check protected circuit Q501, Q502, Q503, Q504 Yes U501, U502 fail IC501 fail T501, T502 fail END ViewSonic Corporation Confidential - Do Not Copy 38 VA702-1_VA702b-1

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ViewSonic Corporation
Confidential - Do Not Copy
VA702-1_VA702b-1
38
5.
Backlight can’t be turned on
Is there high-level voltage
on pin8 of IC501?
Is there pulse waveform on
pin1, pin3, pin15 and pin16 of
IC501 at the moment of restart?
Check CN501,
CN502, CN503 and
CN504?
No raster?
LED Green?
Yes
Yes
Yes
Backlight cannot be
turned on.
No
Check power
supply
No
Is R526 Ok?
Check I/F
board
Yes
R526 open
No
Yes
No
Is Ok IC501?
Yes
U501, U502 fail
No
IC501 fail
Yes
Is ok T501, T502?
T501, T502 fail
No
Connecting the
output connector
again
No
Check protected circuit Q501,
Q502, Q503, Q504
Yes
Yes
END
Is there 14Vdc voltage
on pin13 of IC501?
Yes