8930g lcd bklt issue

[jasko_jacker]

Hi all,
8930G:
At power up, the lamp goes on but after few second goes off.
I have changed the inverter with no result but the strange thing is that all
signals to inverter remain stable after the lamp has gone off.
I have tried with another lamp tube with no result.

[Andrew F. Ali]

Re: 8930g lcd bklt issue

If the PWM, BL-ON and voltage supply and etc. signals remain stable. The Inverter was substituted by a known good on with correct ratings and the lamp was also replaced. Then look for signs of arcing to ground/chassis any associated connections that may be shorting and causing the shutdown. It is highly unlikely that the main parts and signals are good and yet there is shutdown. Some insulation material has broken down over time somewhere near the HV section.

[tibd]

Re: 8930g lcd bklt issue

Since you say u changed inverter then problem is with the CCFL lamps. Disassemble the LCD and take out the CCFL's and see which one gone bad.

[jasko_jacker]

Re: 8930g lcd bklt issue

With another LCD and new inverter the situation remain the same, the bklt goes on, appears the acer logo and immediatly goes off, but the system don't shutdown.
someone has a full datasheet of MSC1697 (lx1697 should be the same) to check if the signal are correct.

[jasko_jacker]

Re: 8930g lcd bklt issue

Reading on other forums, and as mentioned in an answer, the guilty one is probably one of the two lamps. (probably with another lcd the lx1697 goes in protection because the lamps are not the same size ?)
The lx1697 receives the correct signals but goes into protection. There is a way to disable protection, but in the absence of the schema I do not know how to do it. This link show a possible solution but I don't understand dutch
https://youtu.be/ykKhjwLnvcM

[jasko_jacker]

Re: 8930g lcd bklt issue

Finally I solved this issue by welding two capacitors on the inverter outputs. This repair is empirical and I do not know if it is permanent.

[dellxps15]

Re: 8930g lcd bklt issue

u changed one lamp or both ? because if one lamp is bad, inverter can go in protecion and shut down. test with 2 good lamp, or better 1 of lcd and another lamp and swap to see if it stay on. no matter lamp size.

[infosanvi]

Re: 8930g lcd bklt issue

Hi jasko_jacker

I have an 8920g that was almost destroyed and I changed with patience GPU chip (reball), NEC Tokin, GPU pipe strangled by another thecnician and 19v DC intake cable welding

But I did not knew the backlight problem of these units and is the only thing that remains unresolved

Like more people I discovered that pressing Fn + F6 several times the backlight keeps on when CCFL reaches working temp. Also discovered that using a 120 watt DC adapter the problem reduces a lot even desapearing when bright is at minimum and computer is cold

I bought a new inverter TBD489nr with a weak hope and it wont resolved at all the problem as I feared but I dont want replace the CCFL lamps

I am very interested in your solution of capacitors on inverter but the inverter already has two capacitors in these places you marked with a red circle

Have you replaced the original capacitors ?
Can you tell me a little more ?

Thank for reach this point reading so bad English of mine, sorry