D-Sub Connector Pin Assignment - Dell 1907FPf Service Manual

The voltage signal on Pin2 of ZD4 sensed through R14 comes to Pin8 of U1, ISEN (Lamp Current
Detection & Control). C12 is used to dump noise. Once the CCFLs are ignited and current is sensed through
resistor R14 ,capacitor C12 performs the loop compensation function. The voltage at pin 1 controls the drive
duty cycle of the power MOSFETs to regulate the CCFL current.
2.2.2 Protection Circuit of U1
If a CCFL is removed, fails or damaged during normal operation, CCFL current is no longer sensed
and the voltage on ISEN pin drops. Once the voltage at the ISEN pin is less than the lamp" on" threshold,
the shutdown timer is activated. The IC maintains the output voltage for approximately 2-3seconds and once
the timer expires, the IC will shutdown. To restart the IC, either toggle the ENA_SST_CMP pin or recycle
the power on the VDDA pin.
The control logic protects the transformer from an abnormally high voltage at the secondary output.T1and
T2 output voltage are sensed through Rectifier Diodes Q3.When the voltage at the emitter of Q3 is less
than –Vbe DROP,Q3 will conduct and regulate the output voltage to T1and T2 secondary.
2.3 I/F Board Circuit
2.3.1 RGB CAPTURE
- Signal RED,GREEN,BLUE input through CN301 #1,#2,#3, Stop DC via C303, C302 and C301, and
then enter into U401 (gm5621-LF) analog input terminal #99,#96,#93, and then gm5621-LF deals
with signal internally. D315, D316, D317 are ESD protector to prevent U401 from ESD.
- Signal DDC_SCL (series clock) inputs via CN301#15, and then passes through ZD304 for ESD
protection, goes into EDID EEPROM IC U301 #6.
- Signal DDC_SDA (series data) inputs via CN301#12, and then passes through ZD306 for ESD
protection, goes into EDID EEPROM IC U301 #5.
- Signal TTL vertical sync. (Vsync) inputs via CN301 #14, and then clamped by ZD302 Zener, passes
through R311, and then goes into IC U401 (gm5621-LF) #90.
- Signal TTL horizontal sync. (Hsync) inputs via CN301 #13, and then clamped by ZD301 Zener,
passes through R310, and then goes into IC U401 (gm5621-LF) #89.
- CN301#5 is defined as cable detect pin, this detector realize via R337 and U401#114, and ZD306 is
ESD protector.
- U301 +5V is supplied by PC via CN301#9 with D328 and ZD303 for ESD protection, or supplied by
Monitor self via D304.
- U301 is an EEPROM IC which is memory and VGA input EDID data saved in it.
2.3.2 DVI CAPTURE
- Differential Signal input RX0+,RX0-,RX1+,RX1-,RX2+,RX2-,RXC+,RXC- through CN302
#18,#17,#10,#9,#2,#1,#23,#24 via R330,R327,R318,R321,R317,R303,R331,R335 enter into U401
(gm5621) Digital input terminal #80,#81,#75,#76,#72,#73,#83,#84, and then gm5621 deals with
signal internally.
- Signal DDC_SCL (series clock) inputs via CN302#6, and then passes through ZD307 Zener for ESD
protection, via R328, goes into EDID EEPROM IC U302 #6.
- Signal DDC_SDA (series data) inputs via CN302#7, and then passes through ZD308 Zener for
ESD protection, via R329, goes into EDID EEPROM IC U301 #5.
- CN302#15 is defined as cable detect pin, this detector realize passes through R339 ,go into
U401#114, and ZD309 is ESD protector.
- U302 +5V is supplied by PC via CN302#15 through D330, or supplied by Monitor self via D329.
- U302 is an EEPROM IC which is memory and DVI input EDID data saved in it.
2.3.3 Buttons Control
- Button "Power" on front bezel connects to U401 (gm5621-LF) #125 through CN401 #1, U401 #125
is defined as power on/off.
- Button "+" on front bezel connects to U401 (gm5621-LF) #115 through CN401 #4 via R431
U401 #115 (LBADC control Pin ) is defined as "UP".
- Button "-" on front bezel connects to U401 (gm5621-LF) #115 through CN401 #5 via R429
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