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...

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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.

Step 2: Materials and Tools

You will need:
-Monitor that will not turn on
-Capacitor-you will find out the exact capacitor needed later
-Soldering Iron
-Possibly a prying tool
-(optional) A solder sucker

Step 3: Disassembly

This is specifically for the Optiquest Q9B, but I'm sure most people could figure this out. First, take off the plastic part over the hinge for the stand. Then, remove the two screws shown in the picture. Now, all you have to do is pry the two halves apart with some way, shape, or form of prying implement. They should come apart fairly easily. Make sure not to break any wires possibly attached between the front and back halves. These will usually just be speaker wires, and I don't find them to be very important since I use external speakers, but still try to be careful. The power supply is usually covered, so take the cover off. Now make sure to unplug any wires going to the power supply, and take it out.

Step 4: Find Your Bad Capacitor

Now, on the power supply, you should see a bunch of capacitors. Most of them will look normal, but you're looking for a capacitor that has a brownish-yellowish crusty liquid coming out the top or is bulging on the top. The picture will show it better than I can describe it.

Step 5: Desolder

Now, fire up your soldering iron and wait a minute until it heats up. Mark the negative lead of the capacitor on the board for later use. The negative side is the side with the gray stripe on it. Then mark the capacitor that you need to take out and flip the power supply over, keeping track of the bad capacitor. Heat up the solder on one of the legs and use the solder sucker to remove the liquid solder. Do the same to the other leg now. If you don't have a solder sucker, just heat up a leg, bend the capacitor to pull the leg out a bit, and let the solder solidify again. do the same thing to the other leg and keep repeating until it is all the way out.

Step 6: Find Capacitor Value

Don't throw away the capacitor yet, look at it and find the value of it which should be printed on the side. It will probably not be the same value as mine, so make sure to check. Write down the value and throw away the offending capacitor.

Step 7: Selecting a Capacitor

So, this is where you take the capacitor value that you got from the bad capacitor, and find a new one. I used Digikey, but you can use whatever electronics supplier that you like. Select you capacitor using the filters, and then buy it. Isn't shopping fun!?


*I skipped this step...I had the exact right one in my parts box.

Step 8: Solder in the Capacitor

Now that your capacitor came in, or if you just happened to have one in stock, you need to solder it back into the circuit board. Take it out of the packaging, place it into the holes where the bad capacitor was, making sure the polarity is correct, and then flip the board over and solder the new cap back in place.


Step 9: Put It All Back Together

Now that your capacitor is replaced, plug all the cables back where they should be but don't completely put it back together. Turn on the monitor and, if that really was the problem and you did everything right, then it should show the monitor companies logo, or at least a warning saying, "No Signal". If that happens, then voila, put the case completely back together and it's complete and you can pat yourself on the back. If not, go to the next step.

Step 10: Troubleshooting

If you didn't get the desired result, then theres a couple things you can try.
-Resolder the capacitor in the other way. The capacitors polarities could be backwards, in which case, it wouldn't work.
-Try resetting the memory. I had this on a monitor once that would light up the indicator light but not do anything. I reset the memory, and it worked. Do a Google search for "reset __________ memory". Your model number goes in the blank.
-Try other methods. This might not even be your problem.

I hope this helps somebody, and now I will leave you to fix your monitor.



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    18 Discussions


    4 years ago on Introduction

    I fix LCD screens and LCD TV's routinely, and in my experience they ALL always have the same problem. There are 2 or three bulk caps right at the start of the low-voltage circuit, usually right next to a coil, that are PURPOSEDLY underrated (usually rated 10v for a 9v circuit or similar) by the manufacturer so that they will blow after a year or two (usually past the screen's warranty). Bad caps will not necessarily be bulged, so if everything looks ok visually, start by locating and replacing these caps. 9 times out of 10 they are the culprit. Replace with 16v or 25v rated caps instead of 10v.

    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 !


    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 !!



    8 years ago on Introduction

    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.

    2 replies

    Reply 8 years ago on Introduction

    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.


    8 years ago on Step 10

    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

    1 reply

    Reply 8 years ago on Step 10

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


    9 years ago on Step 5

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

    1 reply

    Reply 9 years ago on Step 5

    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


    9 years ago on Step 10

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


    9 years ago on Introduction

    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!

    1 reply
    Phil B

    9 years ago on Introduction

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

    1 reply

    9 years ago on Introduction

    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.

    3 replies

    Reply 9 years ago on Introduction

    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 Bbasic8691

    Reply 9 years ago on Introduction

    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?

    basic8691Phil B

    Reply 9 years ago on Introduction

    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.