Akai LM-H17CLSA, Service Manual, Page: 26 / 54

9. Electronic Circuit Description
9.1 Main Board Circuit
1) Power
Refer to sheet 7 of PWB-0579 circuit diagram.
DC +12V output of AC adaptor is applied to the LCD-TV through socket P020 .
This supply is fed directly to P017 #1
、
2 (Connector to Inverter) and I010 #4 (Audio
Amp. BA5417). It also p8V for I009 (Audio processor MSP3410) through the
regulator ( RC1117) I011 . 12V is regulated by I014 (switching regulator :
LM2576) to p5V for the whole system. I014 LM2576 is a step-down
regulator ( Buckconverter ) and capable of driving a 30A load. The output voltage of
I014 #2 could be fixed in 5.0V
±
4% tolerance via R106
、
R107 and R108 . In the
event of an short or a overload of external circuit, the internal oscillator frequency will
reduce from 52KHz to approximately 18KHz. This self-protection lowers the average
dissipation of the IC by lowering the duty cycle from 5% to 2%, featured 80
μ
A(typical) standby current. Moreover, if the DC 12V supply drops to less than +7V,
the +5V O/P will turn to low .
The output of I014 #2 5V to Panel via I025 ( MOSFET: MI9933). It’s
also fed into I015 (RC1117) to offer +2.5V supply and I016 (RC1117) to offer +3.3V
supply to other chips.
2) PC Signal
Refer to sheet 1 of PWB-0579 circuit diagram.
The analog R.G.B. video signals are supplied through the
PJ03 ( D-sub connector)
and these three input signals are approximately 0.7Vpp in amplitude. R031
、
R032 and
R033 give resistance of 75
Ω
respectively for impedance matching. These R.G.B.
video signals are AC coupled via 0.047U capacitors C021
、
C016 and C013 , and then
fed into the I001 (AD converter) at #54
、
#48
、
#49 and #43 respectively. Then , R.G.B.
video signals are converted to their digital forms in I001 . The outputs of digital data
including 8 bits red, 8 bits green, 8 bits blue signals are assigned at #70~77
、
#2~9and
#12~19 of I001 , and applied to port A of I019 (Scaler : TP6760) . H.sync & V.sync
are applied to I001 #30
、
#31 and the processed signal taken from #66
、
#64 are fed into
I019 (TP6760) #18
、
#19. CLK signal is taken from I001 (AD9883-140) #67 and
applied to I019 (TP6760) #156. The LCD-TV is designed to have the DDC/2B
functions. DDC communication between the LCD-TV and computer is via PJ03
(D-sub connector ) #12
、
#15 and I004 #5
、
#6. The EDID data have written into the
I004 (EEPROM) in the factory during production , so computer will read out the
EDID from the I004 (EEPROM).
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