Viewsonic VA2431wm bad cap replaces, new problem

[Tom-Servo]

Re: Viewsonic VA2431wm bad cap replaces, new problem

The power LED stays on and I can see the screen if I shine a flashlight on it. I'll try the Inverter test you mentioned and see what I come up with, thanks!

I remembered that I have a spare CCFL from my SFII/mame cab but it's a F15 and 15 watts, going to have to find or buy a 4 watter or so.

Does it still have image (shine a strong light on the panel) or power LED when it goes black or does everything shutdown completely?

If you still have image but no back-light, it leans towards the possibility of a bad lamp. BUT still could be inverter. The only real way to test for bad lamps is to plug in some good ones. Try budm's guide "Inverter testing using old CFL" if you have no other LCD CCFLs.

If you have no ESR meter, then one thing I would try is replacing all the other capacitors in the PSU save the mains filter one (the largest) as you already had a bulged one and it's quite possible the rest could be bad but not showing visible signs.

[Tom-Servo]

Re: Viewsonic VA2431wm bad cap replaces, new problem

After further inspection it seems that one of the 4 CCFL plugs was not in all the way, once I made it snuggly connected it works just fine (had to replace one of the MOSFETs when the black electrical tape didn't hold properly, thankfully bought a 10 pack of AO4620s). It does have a few water spots in it and a bigger one in the top right corner. Is there anything that can be done about that?

[Tom-Servo]

Re: Viewsonic VA2431wm bad cap replaces, new problem

It seems like every time I replace the 2 AO4620s one of the 2 fail in a few weeks. Not sure if it's excessive heat or if another component is causing an issue. The last time I replaced the MOSfets I made custom daughterboards so the chips rest in an area with more airflow. (And it's socketed so it's slightly easier to replace) I didn't open it yet but the MOSfet that failed is the one that caused the LED to fail to light at all.

Any idea of what could be causing this issue and/or any possible fixes?

[Agent24]

Re: Viewsonic VA2431wm bad cap replaces, new problem

Is it always the same MOSFET or either one?

If there is no pattern to which one blows, then you may have discovered why cheap transistors from China are well, cheap. They can often be seconds\knockoffs\re-marked lower spec parts etc etc.

An alternative part from a known good supplier might be a good idea in that case...


If the same one always blows, It could also be a fault with the driver, or a snubber capacitor or such related to that specific MOSFET. Comparing waveforms between each with a scope might be useful in such a situation. I hope someone else has a better suggestion there because I wouldn't know what to look for.

You say originally you had blown capacitor(s) and a dead MOSFET. Possibly the bad capacitor(s) meant damage was caused to say the inverter driver, and it's responsible for the current and originally blown MOSFETs.


I doubt it would be a heat issue, the original parts lasted a long time in the same environment, so assuming your replacements are indeed genuine, they should last just as long as the old ones, at the same temperature.

[cyricdark]

Re: Viewsonic VA2431wm bad cap replaces, new problem

I'd like to thank you for the play by play on repairing this monitor, My vh242 asus power board (715g2824-4-5) had the same problem, i replaced the caps on the power board and it worked for a few weeks then started doing what your is doing, replaced the inverter , same blinking blue light and no picture, I was going to go further but after reading about the problems you had with the mosfets going out repeatedly i just broke down and ordered a new power board from dhgate for 25$, hopefully that'll be the end of it's problems for a little while.