Viewsonic LCD monitor repair - capacitors?

[Tickled_Pink]

I've just been revisiting a 19" Viewsonic LCD monitor we rescued from a skip/dumpster last year. The monitor comes on but the screen only displays for a second before going black. From what I've read, monitor problems typically stem from bad capacitors.

 

I've had a look again at this unit and there are three domed capacitors but no leakage from them (yet). Two are on the power board and there's another on the main logic board. I've managed to identify two (a 33uF 16V and 470uF 25V) but one has a very tight fitting rubber sheath to prevent it touching with a neighbouring component. So far I've been unable to take the rubber sheath off so might have to cut it off and maybe put some cardboard between the components when I replace the cap.

 

As I'm not an electronics expert, I just wanted to make sure that I'm on the right track. Should I just replace these three or should I replace all the electrolytics on the two boards?

[Video]

If it comes on, then cuts off, that sounds like it's drawing to much power to turn the lamp on and shutting it off, could be a fuse....I don't know though, only LCD I ever had to work on, had the tube burned out and I replaced it with a flatlite to get a working (though crappy looking) cheap monitor back when they cost a LOT to get.

[BigO]

Not that I know a thing about the Viewsonic, but just in case...

 

 

I had an HP monitor that did that same behavior. It had an external power supply. The (wrong) PS that I got with it couldn't supply the current the backlight wanted. The monitor detected the resultant supply voltage sag and put itself into protection mode.

 

 

 

 

 

[Tickled_Pink]

The Viewsonic has an internal power board. What you guys are saying is what I suspect is happening ... as soon as a picture is being displayed it's drawing more power than the board is generating.

 

The thing is that I have seen various fixes for this problem. It's usually the capacitors on most LCD monitor problems but I have seen this specific issue fixed on one monitor by replacing a bad transformer on the power board. I'm hoping it isn't that since I'd really be in no-man's land.

 

Edit: Just read this Wikipedia entry. Looks like the three capacitors are failing or have failed. Also looks like I'd be better off replacing all the large can electrolytics.

Edited February 26, 2010 by Tickled_Pink

[eeun]

I've fixed a half-dozen LCD monitors or so, and the majority of them simply by swapping out the capacitors with good ones. They don't always show a bulge, etc. when going bad.

The 470uF is common. You can bump up from 25V to 30V rating, for a little extra headroom.

 

I'm not familiar with the Viewsonics, but the Benq monitors also suffered from bad connections that ruined a pair of transistors:

http://www.electronicrepairguide.com/benq-t705-lcd-monitor-repair.html

 

Best of luck with it! Sometimes it's not the caps, and I've been left scratching my head... but when you get a (nearly) free LCD from a dumpster it's a great feeling.

[Tickled_Pink]

I'll order some capacitors from eBay later today. I'll play it safe by getting all of them, although I'll just try replacing the caps that look bad at first.

 

I'll let you know if it works.

[channelmaniac]

I'll order some capacitors from eBay later today. I'll play it safe by getting all of them, although I'll just try replacing the caps that look bad at first.

 

I'll let you know if it works.

 

 

STOP!

 

Go to www.mouser.com and order them there.

 

Get 105 degree caps that physically FIT where they are supposed to go. You don't know about eBay caps and if they are counterfeit or even if they will be the right physical shape to fit. Mouser has links to data sheets for their caps where you can find the sizes of them to make sure they will fit where needed.

 

As for the rubbery stuff on the one cap, it's probably heat shrink tubing.

 

Raymond

Edited February 28, 2010 by channelmaniac

[ClausB]

My cheap LiquidVideo LCD monitor failed a while ago with bulging caps. I replaced them with Radio Shack caps (it was Sunday and I couldn't wait) and it's been working ever since.

[Almost Rice]

I have just picked up a Emprex LM-2203 and it has the same problems you described. I will open it up and check out the capacitors.

[Prodos8]

I fixed a discarded 19" Acer monitor that exibited the problem you described by replacing several caps on the internal powerboard. I just replaced all the larger ones whether they were buldging (several were btw) or not. I did use the high temp (105c) caps and used the same or a higher voltage rating as I was using parts I had on hand -- I think I ended up replacing several 470uf, a few 220uf and a 620uf (?) cap. The hardest part was getting the monitor apart without breaking the case as it didn't seem designed to be opened for service work. Its been working fine since then. There are probably several different brands that use the same powerboard that are prone to cap failures.

[nathanallan]

All this talk about replacing capacitors is making me want to get a better soldering iron, mine cooked itself (ok, just the tip). But it was a cheapie anyway with a large-ish tip not good for fixing anything smt.

 

GRR I need a new one

[channelmaniac]

All this talk about replacing capacitors is making me want to get a better soldering iron, mine cooked itself (ok, just the tip). But it was a cheapie anyway with a large-ish tip not good for fixing anything smt.

 

GRR I need a new one

 

You'd be shocked if you saw the tip I used for surface mount work. It's pretty big...