How to Test Ceramic Disk Capacitor

In computer monitor, it is frequent used in the screen voltage (G2) line at the CRT board. When it fails, it may cause erratic or intermittently raster bright & dim & sometimes no display.

Adjusting the flyback transformer screen control won't solve this issue. You can isolate the issue as whether if it cause by a defective fly back or G2 line at CRT board. Remove the G2 wire from circuit & measure the screen voltage with a digital multimeter- it ought to have a constant voltage (won't vary). If the voltage is not stable suspect the fly back. If it ok then trace the screen voltage circuit. Usually this circuit consists of only resistors & capacitors. Sometimes a defective CRT socket might cause this type of issue also!

Plenty of times a tech cannot solve this intermittent or no display issue is because their digital capacitance & ohmmeter measured ok on the capacitors. The capacitors in the screen voltage line are usually rated of 102,103, & 472 1kv to 2kv. A 'missed' in checking these capacitors will cause the technician cannot solve the issue, unless they direct replace the capacitor. An intermittent capacitor can pull down the screen voltage causing the display issue.

As mentioned earlier, an ohmmeter with 12v output & a digital capacitance with 3v output are unable to exactly check the capacitor that have the rating of 1-2 kilovolt!

In the event you have the analog insulation tester or meter, the panel will show a short circuit when positive voltage are pump in to check the high voltage capacitor. The voltages that you can select is depends on the brand or model you buy. Some have the range of 50v to 1000v & some have the range from 100v to 500v. It is optional whether you ought to have. In the event you have then it would be an added advantage for you. The other option that you have is to direct replace the suspected capacitor. In my country, you can receive a new in less than US150.00 or you may bid a used unit from eBay.

As for me, checking the little blue resin coated ceramic disc capacitor that have the capacitor code of 104 50v, besides using digital capacitance meter to check for the worth, i also use an analog meter set to times 10Kohm that have the output of 12v to check this type of capacitor. Plenty of times it will reveal the bad intermittent capacitor. You will be shocked to see the capacitance meter checked ok but show a shorted reading when check with analog multimeter.

In the market there is positive brand of analog multimeter that has the range of 100kohm. In the event you open up the cover, you cannot see the 9v battery in it, what you see only the pieces of.5v battery. This type of meter cannot exactly detect the short in the capacitor because the output voltage is only 3volt!

For those of you who involved in repairing monitor, you will agree with me that checking the flyback internal capacitance- often you get the right value.7nf with digital capacitance meter but when you switch on the monitor, you will listen to a 'tick-tick' sound from the flyback. This is because the capacitor is breaking down when under load. In the event you did not do anything with the flyback, gradually the internal capacitance will become shorted & you will need to refurbish the flyback.