Com­puter Mon­i­tor dis­play prob­lems such as no dis­play with high volt­age symp­tom can be caused by many rea­sons. A defec­tive pic­ture tube, a faulty video pre­am­pli­fier IC, a miss­ing heater volt­age, torn sig­nal cable, neg­a­tive G1 volt­age became too high (-120 volt and above), CRT board prob­lems, a miss­ing or low G2 volt­age and etc could cause no dis­play but with the present of high voltage.

In this arti­cle I’m going to show you how to tackle a miss­ing or low G2 volt­age prob­lem. First, you must con­firm if there is high volt­age present at the mon­i­tor. You can use a high volt­age probe to mea­sure the anode volt­age (24 KV) or you can try to lis­ten to the high volt­age sound pro­duced (if you are expe­ri­enced enough) once the mon­i­tor is switch on If the high volt­age is present then your focus should be in the screen grid volt­age (G2) cir­cuit. If there is no high volt­age, then I will explain it in another article.

How to con­firm if G2 volt­age present at the pin of the CRT board? By plac­ing your pos­i­tive probe (red probe) to the G2 point and neg­a­tive probe to cold ground with power on, your meter should reg­is­tered some read­ing. For your infor­ma­tion, cer­tain types of com­puter mon­i­tors, if you place your mul­ti­me­ter to the G2 point it would caused the mon­i­tor to shut down due to the caused of imped­ance load­ing of your meter. Assum­ing you mea­sured a low G2 volt­age say 20 volts dc (a good G2 volt­age is some­where between 250 – 300 + DC volt), the next step you should do is to iso­late the prob­lem to see whether is the G2 cir­cuit that dragged down the volt­age or the fly­back trans­former focus/​screen volt­age divider that had gone bad.

Switch off the mon­i­tor and des­ol­der the G2 wire from the CRT board. Place your probe accord­ingly (red probe to G2 wire and black probe to cold ground) Now, switch on the mon­i­tor and begin to see the meter read­out. If the read­ing you get is still about 20 volts or higher a lit­tle bit then sus­pect a defec­tive fly­back. You can also try to adjust the screen volt­age con­trol of the fly­back. If it already turned to max­i­mum then the fly­back need to be replaced. You can also use a cheaper way to solve it. Use a mon­i­tor blur buster to add in and defeat the orig­i­nal focus/​screen cable and use the cable from the mon­i­tor blur buster to act as focus and G2. Thus, with this method the newly tapped G2 volt­age could be sol­der it back to its orig­i­nal loca­tion and you will get a dis­play when the mon­i­tor is switched on!

Now, what if the read­out from your meter shown 250 to 300+ volts dc when the G2 wire volt­age checked out of cir­cuit? This is a very clear indi­ca­tion that there could be com­po­nents that pulling down the G2 volt­age to 20 vdc. From expe­ri­enced, the resin coated type high volt­age ceramic disc capac­i­tor (usu­ally in the 1–3 KV range) had caused quite a num­ber of mon­i­tors became no dis­play due to the capac­i­tor pulling down the G2 voltage.

If you mea­sure the high volt­age capac­i­tor with a dig­i­tal capac­i­tance meter or tester, chances are very high it reads okay (within the capac­i­tance range). The truth is, you can­not rely on dig­i­tal capac­i­tance meter to test the capac­i­tance value only, in fact this high volt­age capac­i­tor have a high ten­dency to break­down when under full load or oper­at­ing volt­age. The capac­i­tor can only be accu­rately test by a spe­cial meter like the Sen­core LC103 capac­i­tor analyzer.

The cost of this meter is very high, so what I did I bought a Kyoritsu insu­la­tion tester for check­ing the high volt­age capac­i­tor pur­poses. Just clip on the capac­i­tor leads under test and press start, a good capac­i­tor will show some charge and dis­charge read­ing but the spoilt one will remained high and would not discharge.

Replac­ing only the bad high volt­age capac­i­tor made the G2 volt­age rise back to nor­mal and solve the com­puter mon­i­tor dis­play prob­lems. Hope you enjoy this arti­cle and please feel free to drop by web­site to learn elec­tronic repair tips and secrets everyday.

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