Filament Voltage Test - Ceronix 1493 Service Manual

Table of Contents

When replacing either the flyback transformer or the video

board, the filament voltage may not be correct.

Measuring the filament voltage is not accurate using a true

RMS voltage meter, because of the high frequency components,

which make up the filament voltage. An oscilloscope, with RMS

capability, may be used to measure the filament voltage.

Although a visual check of the filament color is a indicator of the

filament voltage, it is a good practice to check the filament voltage if

there is any doubt about this important monitor parameter.

The following filament voltage test is an accurate method of

finding the true RMS voltage to the filament. This is accomplished

by comparing the light output of the filament when it is driven by

the monitor to the light output of the filament with an applied DC

voltage using a loaded photocell.

SETUP:

250V

901

470Ω, CF

62K,852

FR205

853

.033uF, 854

100K, CF

To find the filament voltage;

1. Solder two short buss wires to the filament pins to clip on.

2. Use black tape to secure the photocell over the hole in

the plastic CRT socket connector. Caution: Be sure

not to move the photocell between the two tests.

Record the DC voltage output from the photocell with the monitor running normally.

The monitor should be powered up for 10 minutes before making this measurement.

Turn off the monitor.

Connect the variable voltage, 1 amp, DC power supply to the filament.

The negative lead to the filament ground at the CRT socket pin 10.

Adjust the power supply voltage for the photocell reading, recorded in step 3.

The equivalent filament RMS voltage is now recorded by measuring the DC voltage

at the CRT socket pins 9 and 10.