Proview PL926Wbi 19" LCD no picture

[chuck567]

My Proview PL926Wbi 19" LCD will turn on and work fine for a wile and then starts flickering a bit until it loses it's picuture. After it loses the picture if you turn it off and then back on it will have a picture for about 3 seconds before losing it's picture again. Power light stays on solid at all times. I have checked the the inverter board and vga card and there are no signs of overheating, bulging/busted caps or solder fractures. Also when holding a bright light to the screen you can still see the image. I am kind of at a loss for what to do next. Any help would be much appreciated.

[Newbie2]

Re: Proview PL926Wbi 19" LCD no picture

The backlights in the LCD panel may be bad.

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

Since the lights actually light up I wouldn't think it's the lights themselves. It seems like more of an inverter problem from what I have been able to find on the subject. I just can't find any obvious problems. I am hopeful that someone here may be a little more advanced than I am and can set me on the right path.

[Krankshaft]

Re: Proview PL926Wbi 19" LCD no picture

Capacitors can fail without bulging the tops in some instances and they only way to sniff them out is with an ESR meter.

This tool is around 70 bucks so its just more economical to replace all of the caps on the secondary side of the inverter and rule them out.

However bad caps aside problems like this can also arise from bad solder joints on the inverter board.

These boards get pretty hot in operation and the thermal shock the joints have to go through with the inverter heating up an cooling down due to powering the LCD on and off can crack some joints.

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

I will just go a head and change the capacitors. As far solder fractures I don't see any would they be visible or is there another way to find them?

Thanks

[Krankshaft]

Re: Proview PL926Wbi 19" LCD no picture

I just go over the board with a magnifying glass very slowly if this is what you've already done you can rule them out.

If you still have problems after the recap let us know and we can go from there.

You'd be suprised how many times the problems you describe are from these 2 main causes.

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

Usaully I just buy kits of capacitors but I haven't been able to find any kits for this board. Any suggestions as to brand and series?

I need the following sizes.

470uf 25v 105c 10mm X 16mm

220uf 25v 105c 8mm X 12mm

47uf 50v 105c 6.3mm X 11mm

100uf 400v 105c 18mm X 32mm

220uf 25v 105c 8mm X 8mm

10uf 50v 105c 8mm X 5mm

Any advice is appreciated.

Thanks

[Krankshaft]

Re: Proview PL926Wbi 19" LCD no picture

Here you go:



That is the Panasonic FC datasheet they can be ordered from Digikey that datasheet lists the sizes of their caps.

Just make sure that when you order from them that you compare the manufacturers part number on the datasheet to the one you are buying since many cap values in the FC series come in different case sizes.

For example your 470 uf 25 volts at 10 X 16mm would be Panasonic part number: EEUFC1E471.

You can also do the same with any other top tier cap manufacturer just find one of their low ESR series caps and get their datasheet.

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

I ordered them so they should be here in a couple of days or so.
Does it matter on the overall height of the cap?

Example:

If the current cap is 220uf 25v 105c 8mm X 8mm

Would it be okay to us 220uf 25v 105c 8mm X 12mm

or does th height need to be the exact same?

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

Also I noticed that a couple of the smaller caps don't have vents but otherwise are identical in appearance. Name brands appear different as well NEC on the larger caps and Xunda on the smaller ones without vents. Would the smaller non-vented caps still be electrolytic or some other type of cap?

[Krankshaft]

Re: Proview PL926Wbi 19" LCD no picture

The height doesn't matter you just have to make sure that the cap isn't too large.

I remember when I used to order caps without measuring first then afterward my monitor cover wouldn't fit because I installed a cap that was too large.

If you are going to use a different size make sure that there is enough clearance to put the rear cover back on.

Thats why I always measure the original caps with a digital micrometer first especially in cramped quarters like inside a monitor.

The smaller caps are also electrolytic however the reason that they don't have vents is because they don't contain enough electrolyte to burst the can.

So the manufacturers don't score the top like they do with bigger caps.

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

I did measure them all to ensure I got the right sizes there was just a couple I couldn't find the exact right size for 220uf25v 8mm X 8mm to be exact. I just wanted make sure I could use the taller 8mm X 12mm in their place. there is plenty of room for these so I think I am safe.

I know I am asking alot of questions but I am what people would refer to is a perfectionist and I don't like making mistakes so hopefully you don't mind all the questions.

A couple of the caps were actually glued down one with a thick yellow substance and the other with a white hard as rock type glue, any cluse as to what kind of glue this is?

Thanks again for all your help to this point your advice and knowledge have been extremely valuable and appreciated.

[Krankshaft]

Re: Proview PL926Wbi 19" LCD no picture

There are many manufacturers of capacitor adhesive and plenty of different forumulations out there.

It is just there so the components don't fall out of their holes until the automated soldering process affixes them to the board.

You don't need it for reinstallation simply insert the component making sure that its flush with the board then bend the legs of the capacitor on the solder side of the board to hold it in.

Now solder the legs clip off the excess leads and you're done.

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

Well that didn't go well, now it powers up and just stays black screen. Any idea where I can buy a new invertor board?

[alvarado]

Re: Proview PL926Wbi 19" LCD no picture

Same problem here. I've tested for intermittent connections -- no negative results. I've done a "shotgun" resolder job on the power board -- there were a few lands that were a little gray or may have had hairlines. Again no results. I've copied your list of caps and will go out and buy them to try. I don't know why my customer wants to spend to repair this instead of buying a new unit, but that's to my advantage if I can fix it. Would appreciate any new tips! Thanks.

[Krankshaft]

Re: Proview PL926Wbi 19" LCD no picture

Did you check the inverter driver transistors?

If they are shorted you won't get anything.

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

I replaced the power/inverter board with a new one, and still same thing. Works fine for a while and then starts flickering and then shuts off. Turn it off and back on it stays on for a while and then the same thing. I took the new board over to my brothers as he has the same exact monitor and it works fine in his.

[anno]

Re: Proview PL926Wbi 19" LCD no picture

if you replaced the power/inverter board then the problem is somewhere else. I think the backlights in the lcd panel

[chuck567]

Re: Proview PL926Wbi 19" LCD no picture

Again this is not likely to be a backlight problem as the monitor works for quite some time before losing it's pic. It appears as though it may be heat related, if someone has actually seen backlights fail in this way please feel free to post. I am gonna start looking into the vga board and see what I find there. If anyone knows what the likely cause is I would surely appreciate the 411.

[Krankshaft]

Re: Proview PL926Wbi 19" LCD no picture

If you can try swapping over the LCD panels (if you have an indentical monitor and see if it still shuts down) if it doesn't shut down then its probably the backlights.

It's not uncommon for the inverter to shut down if the backlights are on their last legs. CCFLs aren't like fluorescent or incandescent bulbs they aren't an all or nothing deal (either they work or not).

The can slowly become dimmer emit wierd colors and a slew of other things before they fail outright.

Oh crap speaking of bulbs my 150 watt halogen architect worklight just blew out. I guess it saw me typing about bulbs .

Oh well the quartz case was glowing cherry red for some time now I actually was anticipating an explosion . But the filament just gave way.

You never realize what a help a good bright worklight is until it blows out oh well I'll finish the TV tomorrow when I get another bulb.