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Tips on how to Repair Monitor Display Dim Problem

by:Teeho     2020-06-22
This 17' CRT Relisys OEM Monitor came in utilizing complaint of dark display (can't see back raster). Even though at the front panel through the On Screen Display (OSD), you have adjusted to maximum the back raster still would not show out as well as the whole display appeared quite dim. Normally whenever we see this kind of dim display problem assist head straight to the flyback transformer and adjust the screen (G2) voltage control to increase the voltage to photographs tube so that the display will become brighter again. Somehow, in certain CRT Monitor designs, there is no screen (G2) control (knob) for in order to definitely adjust. It contains only the two knobs for to be able to adjust the focus (F1 and F2 knobs). Since we can't find any G2 control at the flyback transformer, you should always search for internal preset brightness control but unfortunately this model don't even have one. It only has the B+ control and high voltage control preset. Advantages voltage preset has been glued with silicon and we can't simply tune this preset otherwise plenty of will intermittently contact shutdown mode. Suggestion preset left a person personally to adjust could be the B+ control. Yes it is genuine that sometimes in certain Monitor you can tune up the B+ control preset to increase the brightness but it is not recommended resulting from the increase of the B+ voltage increases the stress in the horizontal output transistor (HOT). The HOT may not last long and sometimes will blow in number of hours. In this Monitor, I tried to adjust the B+ preset to see in case the brightness would appear or not nevertheless the outcome caused don't worry to go wider and still dim. If I continue to tune the B+ control, I'm afraid the HOT may blow in a very short time! This is just an experiment only, remember that do not tune the B+ control your good reason. After the Monitor had been used couple of years, the CRT cathodes (emission) may are weak and this caused the display to go dark-colored. In order to increase display to become brighter again, you can increase the heater voltage from 6.3 volt to about 8 to 9 V. Or you can impact the G2 circuit strengthen the voltage without tuning any B+ or high voltage preset in plenty of. In this article I'm touching only on the modification of the G2 circuit. Since the flyback transformer does donrrrt you have the G2 control thus we can't trace from the flyback to investigate the G2 lines. In fact we can trace backward at the CRT board to see at where the G2 wire originated from. Yes it came from the Main board and not off the flyback transformer. Upon turning back the main board, one has the potential to see the small G2 circuit consists of a diode, high voltage capacitor and some very high ohm resistor. This is any G2 circuit your job. The high pulse AC supply came in one of the flyback transformer secondary pin and it feel an Ultra fast recovery diode. The function of the diode is to convert the high ac pulse into DC voltage and appeal of soy voltage capacitor (102 2kv-resin ceramic types) is to use to filter there are various high frequency ripple and then the voltage flow along with resistors and the resistors determines (set) the output voltage. Once you understand how this circuit work you can easily modify the circuit or change vehicles . of the resistors to make the G2 voltage increase. From the picture you could clearly see that by removing the jumper and added from a 4.4 Mega Ohm (2.2M in series with another involving.2 M gave the resulting 4.4 M Ohm) I could easily increase the G2 voltage. You may ask 'How do you get the give some thought to.4 M value?' In fact I tried few high ohm resistor values like beginning with 100 K and then 1 M then 2.2 M before I conclude that 4.4 M ohm have the best display (brightness). If you do remove the jumper (link) the display will become too bright and useless for the client. In some Monitor designs, the G2 voltage can stay in the highest value and if this happen no challenege show up resistor value you change or modify the circuit, the G2 output is voltage is still gonna do it . because the G2 voltage already in the maximum. You is only able lower down the G2 voltage right now there is no way to increase the G2 voltage! If this happen then own to modify the heater voltage to increase the brightness. Conclusion-In fact any kind of electronic circuit, if you truly understand how the particular circuit work, you can go about doing some modification produce the electronic equipment work again. If your electronic equipment is viewed beyond repair, work involved . no harm in trying out any modification method that you may think is the best to resulted in electronic equipment efficient again. In order to do that, you must first equip yourself to have a basic regarding electronics theory. To all your information, the above problem was a shared fault and I've already solved regarding it and made some nice income from a simple 10 minutes job. Have a great day my friend!
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