Filament Voltage - Sony KV-32XBR400 Training Manual

Regulator
The PWM circuit regulates +135Vdc from the secondary power supply
down to 102Vdc. It is driven by H drive pulses from Drivers Q5026-7.
These pulses are amplified and output to HOT T5001/pin 1. To control
the output voltage, the output is sampled and used to change the pulse
width of the H drive pulses. These changes regulate the output voltage to
102Vdc at T5001/pin 1.
Pincushion correction
If the PWM output voltage at T5001/pin 1 were changed, the horizontal
picture size would vary accordingly. A vertical pincushion signal made by
IC201/pin 47 is applied to this PWM stage to increase the picture width
and compensate for pincushion distortion.
The first waveform shows the input E/W (east/west) pin correction signal.
The second waveform is the PWM output. The corresponding modula-
tion (sum of E/W signal and horizontal drive) changes the width of the
output pulses (ch2), but that is not easily seen at this scope's time base.
c h 1
1
T
c h 2
2
C H 1 ! 5 0 0 m V ~
C H 2 ! 5 0 . 0 V = M T B 5 . 0 0 m s
Horizontal Pincushion Correction
Channel Name
1 E/W Drive
2 PWM Output
Time base = 5mesc/div.
c h 1 +
Location Voltage
Cn5505/pin 7 0.7Vp-p
T5001/pin 1 150Vp-p.
102Vdc
39

Filament Voltage

There are two sources of filament voltage. When the set is turned ON,
unregulated 7V from the primary power supply (A board) is reduced by
D5025 and D5024 to approximately (7V-1.2V =) 5.8Vdc. This is the first
filament voltage source used warm up the CRT quickly at power ON.
There is no danger from this unregulated 7V supply. Excessive voltage
on the unregulated 7V-line causes Main uCom IC701 to shut down the TV
set (protection circuit not shown here). Consequently, filament damage
from an unregulated primary power supply is unlikely unless a technician
bypasses the protection circuitry during troubleshooting.
The second filament voltage is applied when the horizontal oscillator sig-
nal produces horizontal sweep. The horizontal output transformer T5001/
pin 8 outputs 7.7Vdc when running. This voltage is regulated to 6.1Vdc
by IC5006 to become the main filament voltage.