Genius 1493, ISO XFR-75W, 2093, 2793, 3693, 1793, 1993, ISO XFR-100W manual Filament Voltage Test

Filament Voltage Test.

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:				903		62K,912												ISOLATED
																		DUAL 1A DC
	10						0Ω	, 904
		0Ω , 902								1N4005								POWER
	11														+
			250V	1N4005								906		10uF+				SUPPLY
									1N4005
			.015uF								18Ω		, 879	895	10uF	0 to 30V	0 to 30V	+	+
	13							905
								8		FIL.	FIL.	10		2.2nF,889
	14		901							0Ω	, 896			11
		RED				CF		RED				BLUE
205Ω	15									0Ω	, 897
					,									12
	16			Ω		7		0Ω	, 898
																+6.30V
	17			470		G2				9	10			GAPS
	18		900							8	11			GND		DVM
		H400							7			12
	19				6											+
	20								6	CELL
			899	GREEN														.150V
									5
													SOCKET					DVM
470Ω , CF
					5							1
62K,852						G1
FR205										877	CRT
853				1K
														XX93
.033uF, 854				CF
														Video Board
100K, CF				855														24.3K

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.

3.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.

4.Turn off the monitor.

5.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.

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

7.The equivalent filament RMS voltage is now recorded by measuring the DC voltage at the CRT socket pins 9 and 10.

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