Sony DTV-01, Manual

Page: 72 / 132

75
Protection Circuit 2
The remainder of the protection sensing circuitry on the G board is shown
in this diagram. It monitors the following items:
¨
+5V OCP
¨
+135V OCP
¨
+5V OVP
¨
+135V OVP
The output of these four sensing circuits triggers two stages:
1. The latch circuit on the G board to shut down the TV.
2. The Main Micro for a visual indication of the section that caused the
protection.
+5V OCP
The +5 volts from Converter 2 is monitored by this circuit for excessive
current. The +5V from D5041 passes through both R5038 and R5076
connected in parallel. If the voltage dropped by these resistors exceeds
0.6Vdc, Q5019 conducts and raises the voltage at its collector. This volt-
age turns on Q5018, which turns on Q5017. A high is output Q5017’s
collector that takes two paths:
¨
Through D5047 to the protect latch, shutting off the TV; as well as
¨
Through D5046 to the Main Micro IC3251/pin 43 to blink the standby
light six times, pause and repeat.
Q 5 0 1 9 N o r m a l D C V o lta g e s
E m it te r B a s e C o lle c t o r
+ 5 . 2 3 V + 5 . 1 4 V 0 V
Excessive current means that there is a shorted part on a board powered
by the +5V line. In searching for the load, never unplug an M board con-
nector when there is +135V present on the G board or the G board’s H.
Driver Q4011 and PWM Driver Q4003 will short.
+5V OVP
The +5 volts is also monitored for excessive voltage by zener D5042. If
the +5 volt line rises above the 6.2V zener voltage, a voltage is applied to
amplifier Q5018 and Q5017 to shut down the TV and blink the light six
times. A higher voltage at the +5V line means that Converter 2 is not
regulating. Measure the +5V line with a peak hold DVM to verify the over
voltage.
135V OCP
The +135V OCP circuit is similar to the +5V OCP circuit. The +135 volts
from Converter 1 is monitored by this circuit for excessive current. The
+135V from D5015 passes through both R5026 and R5101. If the voltage
dropped by these resistors exceeds 0.6Vdc, Q5009 conducts and raises
the voltage at its collector. This voltage turns on Q5020, which turns on
Q5016. A high is output Q5016’s collector that takes two paths:
¨
Through D5022 to the protect latch, shutting off the TV
¨
Through D5013 to the Main Micro IC3251/pin 44 to blink the standby
light two times, pause and repeat
Excessive current demand on the +135V line can be caused by: Horizon-
tal Output Transistor Q4018, FBT 7001, Pincushion Output MOSFET
Q4027, or Dynamic focus correction Q7009 and Q7012.
135V OVP
These parts forming the sensing circuit perform the +135V excessive /
over voltage protection (OVP):
+ 1 3 5 V O V P P a r ts
D e v ic e N o r m a l s ta t e P u r p o s e
D 5 0 1 9 – 2 4 v o lt
z e n e r N o c o n d u c t io n W a t c h e s t h e + 1 3 5 V lin e v o lt a g e
d iv id e d b y R 5 0 2 0 & R 5 0 2 8 .
Q 5 0 0 8 – N P N O F F A m p lif ie s t h e in p u t ( s w )
Q 5 0 0 3 - P N P O F F A m p lif ie s t h e in p u t ( s w )
An exc135V B+ breaks over the zener and turns on both Q5008
and Q5003 transistors on to apply voltage:
¨
Through D5017 to the protect latch, shutting off the TV; as well as
¨
Through D5048 to the Main Micro IC3251/pin 45 to blink the standby
light three times.