LG 42PW350 - Power Supply Basic Operation; Power Supply Signal Path

Power Supply Basic Operation
AC Voltage is supplied to the SMPS Board at Connector SC101 from the AC Input assembly. Rectified by the Bridge
rectifier D101 generates a primary B+. The Power factor circuit generates a Primary supply which can be read at Fuse F301
and F302 160V. This
p
rimar
y
volta
g
e is routed throu
g
h T901 and routed to the Standb
y
5V su
pp
l
y
. The STBY5V
(
standb
y)
is
pyg g
yppy ( y)
B+ for the Controller chip on the back of the board (IC701) on the SMPS and output at P813 pins 13 and 14 then sent to the
Main board for Microprocessor (IC101) operation (STBY 3.46V RUN 5.16V). The Main board will receive +5V_ST (STBY
3.46V RUN 5.16V) which is sent to the +3.3V_ST regulator IC500. The 3.3V_ST is used by the Micro circuitry.
When the Microprocessor (IC101) on the Main Board receives a “POWER ON“ Command from either the Power button
th R t IR Si l it t t hi h (
2 22V
)lld
RL ON
t Pi 15 f P813 Thi d th R l Ci it
or
th
e
R
emo
t
e
IR
Si
gna
l
,
it
ou
t
pu
t
s a
hi
g
h
(
2
.
22V
)
ca
ll
e
d
RL
_
ON
a
t
Pi
n
15
o
f
P813
.
Thi
s comman
d
causes
th
e
R
e
l
ay
Ci
rcu
it
to close RL103 which allows the primary voltage to the PFC circuit (Power Factor Controller) to rise to 390V which can be
read measuring voltage at Fuses F301 and F302 from “Hot” Ground. AC Detection (AC Det) is generated on the SMPS, by
rectifying a small sample of the A/C Line and routed to the Controller (IC701) where it outputs at P813 pin 16 (4.15V) and
sent to P601 to the Main Board where it is sensed by the Audio Processor IC700 pin 23.
When
RL ON
arrives the run voltage +5V source becomes active and is
sent out P813 (5 16V at pin 5 6 and 7)
to the
When
RL
_
ON
arrives
,
the
run
voltage
+5V
source
becomes
active
and
is
sent
out
P813
(5
.
16V
at
pin
5
,
6
and
7)
to
the
Main Board P501. The (Error Det) from the SMPS Board to the Main Board can be measured at pin 8 of P813 (3.39V STBY
and 4.89V RUN), but it is not used. The RL-ON command also turns on the 17V (Audio B+ 17V) which is also sent to the
Main Board. The 17V Audio supply outputs to the Main board at P813 pins 1 and 2 and used for Audio processing and
amplification by IC700.
The next step is for the Microprocessor IC101 on the Main Board to output a high (3.29V) on M_ON Line to the SMPS at
P813 Pin 17 which is sensed by the Controller IC701, turning on the M5V line and outputs at P811 pins 6 to the Z-SUS
board.
The Controller (IC701) also uses the M_ON line to turn on the VA and the VS supplies. (Note there is no VS On Command
i thi t) VS i t t t P811 t th
Z
SUS
bd
P7
(VA i
5
dVS i 1 d2) N t Th V i f d th
i
n
thi
s se
t)
.
VS
i
s ou
t
pu
t
a
t
P811
t
o
th
e
Z
-
SUS
b
oar
d
P7
.
(VA
p
i
ns
5
an
d
VS
p
i
ns
1
an
d
2)
.
N
o
t
e:
Th
e
V
a
i
s
f
use
d
on
th
e
Z-SUS then routed out P3 to the Z-SUB and then out P203 to P312 to the X-Board Right. VS is also routed out of the
Z-SUS P2 pins 6 and 7 to the Y-SUS P206.
AUTO GND Pin 18 of P813: This pin is grounded on the Main board. When it is grounded, the Controller (IC701) works in
the normal mode, meaning it turns on the power supply via commands sent from the Main board. When AUTO GND is
floated (opened) it pulls up and places the Controller (IC701) into the Auto mode In this state the Controller turns on th
e
June 2011 42PW350 Plasma
64
floated
(opened)
,
it
pulls
up
and
places
the
Controller
(IC701)
into
the
Auto
mode
.
In
this
state
,
the
Controller
turns
on
th
e
power supply in stages automatically. A load is necessary to perform a good test of the SMPS if the Main board is suspect.