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CIRCUIT DESCRIPTION
Standby Mode:
4 Green LEDs and the Red LED are lit in the standby mode with the AC applied and the TV OFF;
· D903 Indicating Vcc applied to the Power Supply Driver IC Color RED
· Audio Front 29V Regulator SW+29V indicated by D912 Color GREEN
· Audio Rear and Center 29V Regulator SW+29V indicated by D913 Color GREEN
· STBY+11V Regulator I906 indicated by D949 Color GREEN
· STBY+7V Regulator I905 indicated by D927 Color GREEN
Power On Mode:
When the Power is turned ON, the other LED lights and the Red LED remains lit as well;
· D903 Indicating Vcc applied to the Power Supply Driver IC Color RED
· SW+5V Regulator I907 indicated by D931
LED USAGE:
The Visual LEDs are very useful in Trouble Shooting. Without removing the back cover, some diagnostics
can be made. By observing the operation of the Red and Green LEDs, the technician can determine if the
Sub Power Supply is running or not. The following will examine each LED and how they are lit.
D903 Indicating Vcc applied to the Power Supply Driver IC Color RED
This LED indicates any of four different scenarios,
1. Is there B+ (Vcc) available to the Sub Power Supply Driver IC? LED will be ON
2. Is the B+ (Vcc) available to the Sub Power Supply Driver IC missing? LED will be OFF
3. Is the Start Up Vcc to the Sub Power Supply Driver IC available, but the Run Voltage is not? LED will
be BLINKING.
4. Is the Set in Shut Down? LED will be OFF
As can be see there are two different scenarios that can cause D903 to be off, Missing Start up voltage for
the Driver IC and/or the Sub Power Supply is in Shut Down.
Power Supply Shutdown Explanation
This chassis utilizes I901 as the Osc.\Driver\Switch for the sub power supply, just as the previous chassis
have done. This IC is very similar to the previous versions, however it does differ in frequency, (described
previously) and in Stand-By detection. The Shutdown circuit, cold ground side detection, is routed to I901
via Q905 (the Shutdown SCR). I903 (the Photo Coupler), which isolates the Hot ground from the Cold
ground and couples the Shutdown signal to the Hot Ground side, Q901 the hot ground side SCR and I901
pin (4) (the Vcc pin).
The Power Supply utilizes a Shutdown circuit that can trigger Q905 from 16 input sources. (6 of these are
not operational in Stand by mode). I903 is activated by Q905, applying gate voltage to Q901, which
grounds out the Vcc at pin (4) of I901, disabling the power supply.
All of the Power Supply Shutdown circuitry can be broken down into the following groups;
· Voltage Missing Detection
· Excessive Current Detection
· Voltage Too High Detection
In the following explanation, the Shutdown circuits will be grouped. This will assist the Service Technician
with trouble shooting the Chassis, by understanding these circuits and having the associated circuit routs, the
technician can then Divide and Conquer.
