Hi James,

Thank you for the encouragement.  I have a Dell 1800PF LCD monitor.  The monitor went black several months ago (power LED has green).  I have read through your LCD monitor repair book.  I still could not find where the problem is.  Here are my checking results:

1.  The power board seems okay.  All capacitors look normal.  The output connetor has 8 pins, where 2 pins have 12V output and 2 pins have 5V output.  The other 4 pins are ground.

2.  The invertor board input connector has 8 pins, where 3 pins (pin 1, 2, 3) have 12V, and the rest of the pins have 0V.

3.  If the on/off pin should have 3.3V, the on/off signal is probably not there.

4,  There is no burned resistor, capacitor, diode or transistors observed. I don’t have the schematics.  What do you suggest to check next? 

First you need to find out the inverter ic schematic to locate the supply pin. Make sure this pin must have the right supply voltage. Sometimes black does not mean it has no picture. it could have faint picture. Assuming it has the supply voltage next thing you need to check if the backlight connector have any ac voltage. Probably about 500 to 800 vac. Test it with analog meter. If there is no voltage at all then compare the ohm reading of the top and bottom high voltage transformer. Make sure the primary and secondary winding did not open. If you have the scope you can check the output waveform of the inverter ic. Please let me know the status of this repair case.



HI Craig,

Hi! How are you today?

I’m fine here-thanks.

I am fine here and please if you dont mind, I would like to know why does the LCD desk top monotor shut dowm immediatly after switching it on can you please explain that for me

Bad supply voltage, dry joints in inverter board, bad backlight.

because its my personal computer which I use. I opened in and and checked there is a DC voltage on 300Vpresent at the 1st stage filter but I cant get futher I also checked there are 2 other filter capacitors that are at the 2nd stage which are buldged a bit I took them out and checked them with the meter and they seem ok

You need to directly replace it eventhough it test ok with your meters. I guess this could be the problem

and I also checked the transistor # KA431AZ which is a programable shunt regeluator near the opto coupler but I dont know weather that is faulty or not it comes in a package TO-92. led 1 is ref and led 2 is anode and led 3 is cathode. can you please help me as how to check if this transistor is good or not and and please let me know what could be the symtims for the monitor to shut down because I replaced another monitor with the same cpu and that monitor works well. 

TL431 can’t be tested using meter because a bad one will give you a good reading. I suggest that you directly replace and retest. I suggest that you replace the bulged caps and retest the set again.



Thanks for your assistance. is the LCD panel changeable, what is the cost and where I can purchase it

Hi Kissoondath,

Yes the lcd panel can be replaced but very difficult to get parts. You can try ebay.com or you can email luca at info(at)lavinci.it to check if he has the panel or not.



Hello  Mr.Jestine,saya perlukan pertolongan anda.Saya sedang membaiki sebuah LCD Monitor brand Acer Model AL1711 yang
mempunyai masalah NO POWER.Saya telah cuba replace IC PC123 dan juga UC3842 IC tapi masih tak boleh switch on
dia punya power.Saya juga sudah test power fet dan power fet dalam keadaan baik.

Encik Jestine tolong beri sedikit tips apa lagi yang perlu saya check?Saya dah check hampir kesemua komponen dan saya dapati
komponen-komponen tersebut dalam keadaan baik.Mungkin ada yang saya terlupa nak test?Saya harap Encik Jestine dapat membantu
saya…PLEASE..Disini saya ada sertakan gambarajah PCB bahagaian power tersebut.

Sila lihat gambarajah tersebut menggunakan Paintbrush lagi jelas gambarnya.

Sekian..terima kasih.

HI Noorishkandar,

Sekiranya output totally kosong volt, make primary side masih ada masalah lagi. Kalau ada sedikit voltgan, kemungkinan TL431ic (berdekatan dgn PC123) ada masalah ataupun ada komponen short kat bahagian inverter ataupun mainboard. Berapakah voltan supply dc kat kaki vcc uc3842? Sekiranya inverter board ada fuse, sila keluarkan fuse dan power on. Kalau voltan output kembali maka ada short circuit kat inverter circuit.



Hi Mr Jestine!

Bolehkah Saudara hantar gambar/video dimana bahagian/component di monitor pc yang bermasalah kehilangan”

‘Warna hijau’ dan cara2 membaikinya.



HI Musdi,

Try check link tersebut:




hello mr jestine . I have a problem with lcd monitor ( model: hans HI 221); when I power on this monitor I get a white screen for one or two seconds then the screen become black ( the led remains green ). I don’t KNOW if this is a problem of inverter or main board or both. CAN YOU HELP ME


HI Achour,

Check for correct voltages first from the power supply. If the display turn black make sure the inverter ic is still getting the supply voltage. Sometimes the problem can be a bad cable connection between the mainboard and the lcd panel.


Comments are closed.