LM721A
Service Manual Rev: A
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8.2 Trouble Shooting
8.2.1 Main Board
1.NO SCREEN APPEAR
Note: 1. if Replace “
MAIN-BOARD
” , Please re-do “DDC-content” programmed & “WHITE-Balance”.
2. if Replace “
Power Board
” only, Please re-do “ WHITE-Balance”
Measured CN402 pin 9/10 = 2.5 V?
Measured CN402 pin 7/8= 3.3V?
Measured CN402 pin 3/4= 5V?
Measured CN402 pin 12= 12V?
Check Correspondent component.
Is there any shortage or cold solder?
Yes. there have OSD show
Yes, all DC level exist
Disconnected the Signal cable( Loose the
Signal cable ),Is the screen show “Cable Not
Connected” ?
Connected the Signal cable again,
Check LED status.
Led Green
Replace U202
Flash Rom
No, nothing is show
Connected the Signal cable again,
Check LED status.
Check Power switch is in Power-on
status , and check if Power switch had
been stuck ?
Led Orange
OK, Keyboard no stuck
Led orange
Led Green
Check the Wire-Harness from CN301
Measured RGB (R133,R134,R135) H,V Input
at U106 pin 4,10 ,was there have signal ?
Measured ED101~ED108 (GM5120 only)
Check digital signal from CN101
Check Correspondent
component short/open
( Protection Diode )
NG
OK,Wire tight enough
Check
Panel-Power Circuit
Block
OK,Panel Power OK
Check
U203 Data-output
Block
OK, U203 data OK
Replace
Power board
and Check
Inverter
control relative circuit
Re-do White balance adjust
OK,input Normal
Measured Crystal X201(14.318MHz)
OK,clock
Replace
U203 (GM5120/2120)
OK
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