iiyama ProLite H481S - random flickering and/or blank screen

[BC1]

Hi guys! Great forum, I've done a lot of reading here the past couple of weeks but still can't seem to fix my problem.

Few months ago, my 5 year old iiyama ProLite H481S started flickering randomly. In the following weeks, it started just going blank entirely once every week or so.

The power LED would remain active - I would have to turn my LCD off and on to turn the backlight back on. Sometimes it would turn right back off. Hitting on the LCD (why?) would suddenly get it to work again and stop the random flickering for a week again.

Recently, these problems have been happening almost on a daily basis. Thought it might be a good idea to see if I can repair the thing while it's still dying, rather than wait for a power surge or something bad to happen.

So, I started Googling and came across this forum. Figured it only makes sense that capacitors lose capacity after a couple of years - wondering why I hadn't thought of it myself, as I'm studying electronic engineering and all . It could explain the problem of said flickering and blank screens.

Opened up the monitor, inspected the caps and resistors, but seriously did not find ANY clue as to what's going on.

So, I whipped out my camera and recorded the inverter/power-board and figured I'd post it on the interwebs, see what you guys think about it. Maybe I'm missing a clue, or maybe the board is just fine and I need to look somewhere else.

The backside of the board is fine too, by the way. No rust, leakage or anything bad going on there.

I didn't dare opening up the LCD unit itself (a Samsung LTM190-EX), because I'm not sure if the problem could even be in there. Can it?

Video: http://www.megavideo.com/?v=DOE8M110
Image: http://img849.*************/img849/4299/sam0395.jpg

Can you guys advise me? What do yall think of the video and image I attached?

Thanks in advance for any advise!

[retiredcaps]

Re: iiyama ProLite H481S - random flickering and/or blank screen

Can you guys advise me? What do yall think of the video and image I attached?

1) There are a number of reasons why we ask people to use the manage attachments function here, but I took your 5MB 4000x3000 resolution picture (good clarity and focus) and resized to fit on this forum (2000x2000 max resolution). The new file is 395KB (a 12x reduction). We also ask new members politely not to post inline.

2) Do you have a multimeter?

3) Caps do not have to bulge or bloat in order to be bad. They can measure incorrect uF. For example a 1000uF cap may only measure 50uF.

[BC1]

Re: iiyama ProLite H481S - random flickering and/or blank screen

retiredcaps, thank you for your reply. I linked to a large image because I assumed people would need to see the photo in high resolution. Thank you for adjusting it to the forum rules, either way.

Yes, I have a (cheap) multimeter. Would I have to solder the caps off before I can test them? Which multimeter mode would I have to look for to test the caps? I have not measured a capacitors F value before. I'll have a look in the multimeter manual, as well.

[Th3_uN1Qu3]

Re: iiyama ProLite H481S - random flickering and/or blank screen

A regular multimeter (even one with capacitance measurements) will not help too much with bad caps. You need an ESR meter for that.

The good news is that you were asked for a multimeter to take voltage measurements, which your cheap meter will do just fine.

[retiredcaps]

Re: iiyama ProLite H481S - random flickering and/or blank screen

1) If you hookup a working computer with your favourite wallpaper, can you see it if you shine a flashlight on the lcd?

2) When the lcd dies, does the power LED stay lit?

3) Get the lcd monitor working and measure the DC voltages on CN902 for all the connectors. Be careful and don't let the probes slip to cause a short.

4) When the lcd dies, measure the DC voltages on CN902 for all the connectors. We will then compare with the DC voltages taken in #3 above.

[BC1]

Re: iiyama ProLite H481S - random flickering and/or blank screen

@ the_unique: Great, I know how to measure voltages - let me know what you want me to measure. Keep in mind though that at this point the problem appears randomly, not constantly. It will be hard for me to measure voltages during the flickering. I want to repair it before the caps or backlight completely dies.

[Th3_uN1Qu3]

Re: iiyama ProLite H481S - random flickering and/or blank screen

I'll let retiredcaps ask these questions, he's more knowledgeable in this area and tends to have a bit more patience than i do.

If certain points are hard to access for measurements when the monitor is working, solder wires to them and bring them outside. Be sure to label the wires and avoid shorts though. A good idea is to tape the wires to the desk.

[BC1]

Re: iiyama ProLite H481S - random flickering and/or blank screen

@ retiredcaps thank you for your guidance.


1) Yes, it's just a backlight problem.

2) As stated in my original post: yes, power LED stays lit after screen goes blank.

It's gonna take a few days for me to complete step three and four. Thank you so far.

[BC1]

Re: iiyama ProLite H481S - random flickering and/or blank screen

Good idea, the_unique!

[retiredcaps]

Re: iiyama ProLite H481S - random flickering and/or blank screen

Hmm, if it happens randomly, it could be tough to get the measurements.

At this point, I suggest looking at all the solder joints on the backside and making sure they all look okay. If they look suspect, reflow or resolder them. Pay attention to the soldering on the inverter transformers.

I don't know of any multimeter that will measure ESR (ohms), but some multimeters will measure capacitance. Even then, you will probably have to desolder the capacitor to get an accurate uF reading.

[alexanna]

Re: iiyama ProLite H481S - random flickering and/or blank screen

Hmm, if it happens randomly, it could be tough to get the measurements.

At this point, I suggest looking at all the solder joints on the backside and making sure they all look okay. If they look suspect, reflow or resolder them. Pay attention to the soldering on the inverter transformers.

I don't know of any multimeter that will measure ESR (ohms), but some multimeters will measure capacitance. Even then, you will probably have to desolder the capacitor to get an accurate uF reading.

Also

If voltages appear stable, And I have a symptom of flickering of the LCD,The first thing I would rule out would be a CCFL problem most likely wiring that's effected by heat.
A poor solder connection on the secondary side of the inverter, again affected by heat.
Or an inverter coil winding that's opening up when it gets hot, you may be able to pick something up by measuring resistance cold and hot.
These are things I can do very quickly, and get a good idea if these are problem areas. or if I need to move on and check other areas.

[PlainBill]

Re: iiyama ProLite H481S - random flickering and/or blank screen

Since it reacts to being hit (you brute!!!), it points to a bad solder joint, most likely on one of the leads to the CCFLs.

PlainBill

[alexanna]

Re: iiyama ProLite H481S - random flickering and/or blank screen

Since it reacts to being hit (you brute!!!), it points to a bad solder joint, most likely on one of the leads to the CCFLs.

PlainBill

I missed the part about the hitting monitor.
I have had to many problems with CCFLs,after a good visual of the board and bulging capacitors the CCFLs are at the top of my list to rule out.
I am lucky I can just plug in a good set of CCFLs and see if it makes a difference. There are times where the monitor has to be partially assembled to let heat do it's thing.

[BC1]

Re: iiyama ProLite H481S - random flickering and/or blank screen

Yes, it makes sense that hitting the monitor would only bring it back to life if it were caused by bad soldering or bad CCFL mounting.

How would you suggest to disassemble the actual LCD module (which contains the backlights)? I've been unable to find a good tutorial for it. I'll give it another Google in a bit.

Just a heads up, after having dis- and reassembled the monitor, the problem disappeared (for now). I do have some light flickering going on once every 3-4 days, but the display no longer goes black.

I'm assuming either I gave some bad soldering point (if that's causing the problem) an accidental nudge the right way, or the removal of dust on the board is preventing heat from reaching the critical levels (if that's causing the problem).

Thanks again for all of your help. I will keep sharing my experiences to improve our shared knowledge .

[Scenic]

Re: iiyama ProLite H481S - random flickering and/or blank screen

if you're lucky, the CCFL assembly will slide out at the side. seen that on LG-Philips panels.

like so
https://www.badcaps.net/forum/showpo...53&postcount=2