Fix a Malfunctioning LCD Power Supply

So I got five of these Optiquest Q9B LCD monitors from where my dad works, thinking I could use them for something other than monitors. The problem was, they just didn't even turn on. The problem was the same in all of them, so I'm guessing it is a pretty common problem for these monitors. I have also seen other LCD monitors being repaired this way, so it's worth a shot if your monitor doesn't work.

DISCLAIMER: The power supply in these monitors can potentially carry a lethal current in them. I am not responsible for anything that could happen by your following my instructions.

Not sure if that was necessary, but I want to protect my ass just in case...

Step 1 A Little Bit of Background

In LCD monitor power supplies, the capacitors will occasionally go bad. This causes them to leak and bulge out and the power supply will not be able to provide power to the monitor, causing it to not even turn on. So yeah, this is quite a problem if you want the monitor to work.

Comments

[offtherails2010]

Absolute-Excellence-In-A-Can !

A very well put together and well explained instructible !

I've had a monitor i bought from brand new, only a humble 19" monitor, and really didnt want to throw it away bcoz it only lasted 2 years from when i bought it !

Damn-Cheap-Shi*...

Anyhoo, i'll be doing this repair hack as soon im physically able-to !

Will post me results no matter what outcome & a great many thanks for the info !!

;-)

[kazots]

I tried this and was killed instantly! So I guess this is a ghost post! :>)

Thanks for this instructable. I have a Samsung 24" monitor that has assumed room temperature and have been told it's usually a prob with the capacitors. We shall soon see and if I can fix it and will sing your praises if I do.

[LuminousObject]

Haha allright. Good luck!

[kz1]

Well I took the ol' monitor apart and not a single thing looked bad on the inside. I got on the net and went to Fix-ya to hook up with a seasoned monitor tech. He/she said didn't think it was a capacitor prob and gave me a bunch of stuff to check for.

So I put it back together and I'm using it now for a bout 15 min and it hasn't screwed up yet. It will I think cuz it made that popping noise through the speakers again after I got it hooked up and turned on. With this 24" and the 28" sitting next to it, this is a heck of a lot of video real estate! I like it.

I just hope I can find out what's wrong with this thing and fix it. I'll post more if I find out anything definitive.

[niceribs]

Has anyone tried this with success ? I hope you have.... there are a lot of sick capacitors in a wide variety of electrical goods these days...
ps great instructable

[LuminousObject]

Yep, I did this with 4 of these monitors, and it has worked every time. Thanks!

[motrocco]

quick question - how do I make sure that this is is still not charged? I don't want a shock if possible. great instructional

[LuminousObject]

The easiest way is just to take an insulated screwdriver and short out the capacitor. Make sure that the screwdriver is insulated though, otherwise you will get a shock. Good luck! And be careful

[calanick]

i will try and c what happends. if work ill be grateful to you.

[ironsmiter]

Unless your budget is low, I'd replace ALL the capacitors on the power board.
Even the ones not bulging might have dried out. Especially if it's an older lcd(oldest model I've recaped was an Apple Studio display 15" from 10 yeas ago). Newer lcds, bulging or leaks are an adequate indicator.

Of the Dozen or so lcd's I've recapped, 3 have needed more caps replaced within months of being returned to service.  It's almost always the larger, higher voltage caps that go. So, if you're gonna replace one bulged, look for similar valued caps nearby, and do those too, while you're at it :-)

And happy hacking!

[LuminousObject]

Allright. :) Thanks for the input.

[Phil B]

I do not have one of these monitors, but thank you for a good and helpful Instructable.

[LuminousObject]

Thanks. :)

[basic8691]

First off, a word of caution: if you have little electronics experience, don't try this. Switching power supplies work by rectifing and filtering mains power, thus creating a input voltage of 155 VDC (from 110 VAC) or 310 VDC (from 220 VAC) and then switching that voltage through a high-frequency transformer, to be reduced, rectified and filtered on the output side. So not only there are potencialy fatal voltages and currents flowing but these voltages remain for some time after desconnection. If you want to follow this article, make sure that the power supply is disconnected from the mains for at least one hour before touching it.
Secondly, the kind of capacitors refered (called electrolytic) don't take nicely to reverse polarity; normaly they explode. So make sure you install the new capacitor as the old one was (match the arrow on the side of the capacitors).
Thirdly, the old capacitor has two values written on it: it's capacitance and its voltage rating; you need to find a capacitor with the same capacitance (normally indicated in uF) and with the same or greater voltage rating. NEVER put in a capacitor with a lower voltage rating.

[LuminousObject]

Ummm...did you actually read all of what I had written? The capacitor that I replaced was the exact same values.... And since I think it will make you sleep better at night, I'll add some more warnings. Thanks.

[Phil B]

Items like a cathode ray tube can be discharged before getting close to them, if done properly and with care.  Is there a way to discharge any stored charges in these power supplies?

[basic8691]

All switching power supplies have high-voltage-rated electrolytic capacitors (at least one) on the input side; they're the biggest on the board and will typically be rated for over 200V. You can use a 1 KOhm / 10W carbon resistor to shunt that capacitor's pads on the circuit board.DO NOT HOLD THE RESISTOR WITH YOUR FINGERS. Use plyers with isolated handles. And be prepared that it may spark on contact but with a 1K resistance the current will be relatively small.