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should
be present.
If not, the Standby
Power
Supply
circuitry
should be repaired
or the Module should be replaced.
If the Standby
Supplies
are okay and the Full Power
Supplies
do not come up to normal voltage,
repair the Full Power Supply
or replace
the Module.
The 130V-A Source
is available
from
P402-1, while the 130V-B Source should be present at two loca-
tions, P404-5 and P404-6.
The 130V-C Source can be checked
at P404-7.
The 9V and 15V Sources
can be checked
at P402-5
and P402-2 respectively.
If only one voltage is missing,
that cir-
cuit can be repaired
to restore the complete
Power Supply.
There is also a Fuse, F404, which is soldered
into the PCB for
the 26Vdc
Source.
This voltage
source
is used by the Audio
Amplifier.
Some
boards
may be labeled
as L412 for this fuse
location.
Later boards will show the fuse as F404.
Deflection Failures, Video Blanking, and High Voltage
Shutdown
The CRTs in a Projection
Television
can be damaged
if deflec-
tion stops
and the beam
current
is not stopped
immediately.
The CRTs can be damaged
if the beam is allowed
to be On for
as little as a thousandth
of a second
with no deflection.
It is
important
NOT to defeat the deflection
failsafe
and CRT phos-
phor protection
circuits
as shown in Figure
11.
If horizontal
or
vertical deflection
circuits are not operating
properly,
blanking
of
the video will occur from the collector
of Q500.
Keep in mind, a
failure
of the protection
circuits
can also cause
blanking
of the
video or shutdown
of high voltage.
With a set operating
normal-
ly, Q501, Q502,
and Q904 are turned
Off.
Q500 is turned
On
which
allows
a High level to be placed
on the Blanking
line.
This High level allows the picture tubes to operate,
while a Low
level will cause the CRTs to shut Off.
Vertical and horizontal
deflection
waveforms
are peak detected
by Diodes D502 and D504.
These voltages
are stored in capac-
itors C501 and C503.
The capacitor
is discharged
by a resistor
so that if deflection
stops, the capacitor
will be discharged
and
blanking
will be activated.
An oscilloscope
can be used to verify
the proper
operation
of horizontal
deflection
by looking
at the
cathode
of D503.
For Vertical deflection,
IObk at the cathode
of
D501.
If the lowest voltage
at either check point drops below
approximately
15 Volts, blanking
will occur.
If the 15 Volt supply
is not high enough,
Z500 will not be conducting
(voltage
less
10
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