Picture Tube Defect Symptoms - Sony WEGA KV27FV15 Training Manual

Picture Tube Defect Symptoms

Overview
Below is an excerpt from the CTV-25 course. It shows several picture
tube defect symptoms, some of which can be repaired without changing
the tube.
Defective Picture Tube Symptoms
Symptom Suspect
Dark picture or Heaters
one color Open
missing.
Dark picture Grid 1 to
Grid 2
short.
Bright red, Heater
green or blue Cathode
picture. short.
One color
OR
retrace lines
Cathode to
may be
Grid 1
present.
short.
Retrace lines
are diagonal
lines that run
from lower left
to the upper
right corner.
Check Procedure
Apply 6Vdc to Clean the CRT pins and
the heater examine the socket for
terminals. corrosion.
Some heaters Apply 6Vdc to the CRT
are connected heater pins, looking for a
in parallel, glow in all three heaters.
others in Then if a heater(s) does not
series but all glow, replace the picture
take 6Vdc. tube.
There should 1. Unplug TV and remove
be infinite C board.
resistance 2. Apply 15-20Vdc
between the between the G1 and G2
G1 and G2 pins to vaporize the
pins. short. Current limit the
power supply to 1 Amp.
Remove the Replace tube.
R, G or B
video input to
the CRT for
the bright
color. If that
color is still
bright, the
tube is bad.
There should
be infinite
resistance
between any
CRT pin to
either Heater
pin. *
3
Bright picture Grid 2 to
with retrace high
lines and/or voltage
poor focus. Grid 3
leakage.
RGB Rainbow. Aperture
(see rainbow grill was
picture) unseated in
transit.
Purity / Beam The TV s
landing is off. degaussing
circuit did
not
demagnetiz
e aperture
grill metal
support.
* Only the heater pins should have resistance. All other pins have infinite ( ∞ )
resistance to each other and to either heater pins.
Used picture tubes that have a heater-cathode leakage/short have a low
restoration success level.
** Do not manually Degauss. New 27
conditioned for optimum beam landing. Strong manual degaussing will
destroy this conditioning. Applying disc magnets (P/N = 1-452-094-00) to the
bell of the picture tube is the only way to compensate for lost magnetic
conditioning. The Sony manual degaussing tool can be used to degauss
these tubes because of its reduced field intensity (P/N = 7-700-781-01).
Symptom is Reduce G2 / screen voltage
that all three to the lowest setting.
colors are
Vary focus control to both
bright.
limits several times.
Put on safety apparel.
Place the tube face down
and lightly tap the neck to
dislodge the particle.
Rainbow of A loose aperture grill is
colors can dangerous and may cause
start at the top tube implosion. Use all
or bottom safety precautions. Do not
(bottom jar set. Transport TV face
rainbow down.
shown).
Same color Do not manually Degauss
blotches the picture tube with a
remain at that strong degaussing coil **.
area of the Repair the TV s degaussing
screen circuit. The thermistor or
regardless of cold solder is usually at
picture screen fault.
changes.
35 picture tubes are magnetically