Ballast Circuit
This chapter of the book is divided into 6 sections:
1. Lamp On Sequence Chart
4. Ballast Block Operation
2. Ballast Board Layout
5. Testing the Lamp and Ballast
3. Ballast Board turn-on voltages
6. L Board LED Indicators
Lamp On Sequence Chart
Lamp On
Operation
Voltage
Test Location / Verification
1
Press the power-on button.
Stby 7Vdc
TP on PS bd. next to P4
2
The TV’s microprocessor turns on the
ballast power supply stage on the P power
supply board.
+335Vdc
Ballast Bd. B1/pin 1. Use Pin 3
or CN005 as (floating) ballast
ground.
3
The Microprocessor initiates a ballast turn-
on command. (5 seconds after power-on
button is pressed.)
2Vdc
(High)
Ballast Bd. B2/pin 1.
Use chassis ground or pin 2
(cold ground).
4
The ballast circuitry generates over 20kV to
ignite the lamp.
20kVac
Lamp On (ignition). Low to full
brightness in 1 minute.
5
The ballast control circuit grounds B2/pin 3
to inform the microprocessor that the lamp
is drawing current (lamp turned on).
0Vdc
Ballast Bd. B2/pin 3.
Use (cold) chassis ground.
Lamp Off
6
Press the power-off button.
7
The Microprocessor ballast turn-on
command goes low. A/V is muted.
0Vdc
Ballast Bd. B2/pin 1.
Use (cold) chassis ground.
8
Ballast stops the 20kVac supply to the lamp.
Lamp goes off.
9
Microprocessor keeps fans running for 20 seconds longer, and then shuts the TV off.
Table 9
Ballast Board Layout
Ballast Board Connectors
B1 Connector B2
Signal Name
Input /
Output
Pin
Signal Name
Input /
Output
+335Vdc supply
voltage
In 1
Ballast-On
from
microprocessor
In
No connection
2
Cold ground
In
Floating ground
In
3
Lamp On
Out
Table 10
Ballast Board Requirements
Refer to tables 10 & 11. The ballast assembly produces HV for the lamp when the two
voltages listed in table 11 are input. Notice that the ballast operates, using hot ground
but a cold ground microprocessor signal is also needed.
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