LCD Monitor problem

Ray: I have a Gateway FPD1730 which I think is a LG708G (CL-36) which has a simular problem. Most of the time, it is completey dead. Every one in a while, it will come on when I am working on it. Last night, it came on and I ran it until bedtime. Turned it off, then on, several times. Worked good. This morning -- dead again. There are three circuit boards, besides the panel (made by Hyundai). The Power supply, controller and front panel switch board. I believe the problem is in the controller board. Voltages on the power supply are working correctly. There is just no Enable signal from the controller to the PS board. I replaced most of the SMD electrolytic capacitors on the controller (many had high ESR), but still no improvement on starting up. I called LG parts and gave them the part numbers on the controller and the LG model number. They told me that they had no record of the intems in their computer. When I mentioned that is was a Gateway (made by them), they told me it was an OEM item and they do not supply these parts... Go see Gateway. Gateway told me that they do not sell parts and to send the LCD display back to them for repair (it is out of warranty). I will not do this. They are too expensive. Let me know how you make out with yours... John

mccrary wrote:

First try a new CCFL tube, just wire it up to the inverter without installing it in the display and see if it runs correctly, if it does then you found the problem. When they age, the voltage required to sustain an arc increases. It could also be a faulty inverter but the tube is more likely since it lights at all.

I've got a problem with an LCD. It powers on, but I can't get a picture from it no matter which of the 4 inputs is plugged in. I opened it up to look around, check connections etc.

As I was testing voltages at several points, I think I must have shorted two points at some point, because I noticed that the monitor had come on and I could see the built in on-screen display. So I know that the monitor itself and the backlight work.

But I still can't figure out how to get it to actually detect input and turn on.

Any thoughts on what the problem could be?

You will need the service manual, which I doubt you would be able to obtain, and the proper set-up and spare parts to service your monitor. If it is a very expensive monitor, you should send it back to the manufacture's service people to have an estimate. You may find it more feasible to replace the monitor.

--

Jerry G.

As I was testing voltages at several points, I think I must have shorted two points at some point, because I noticed that the monitor had come on and I could see the built in on-screen display. So I know that the monitor itself and the backlight work.

But I still can't figure out how to get it to actually detect input and turn on.

Any thoughts on what the problem could be?

Well, I could get the service manual for about $25 online for this model, so I may just do that.

I've managed to get it to turn on semi-consistently by briefly shorting two pins on the Analog Devices AD9884A chip. When I short them there's a high pitched buzzing that seems to be coming from the power supply, then I release the short and the signal light goes green and I can access the on-screen display. If I then do a Reset from the menu, it correctly locates the input signal and shows it. However, I still can't switch to other signals through the buttons, and if I try to use the +/- buttons to switch display, I can no longer even get into the on-screen menu.

Additionally, shorting those two pins doesn't work EVERY time, just regularly.

I suppose it probably is best just to buy the service manual, though I'm not sure it's going to offer any better suggestions.

I really wouldn't recommend shorting IC pins... you can easily destroy them, if that hasn't already happened. The IC AD9884A is an analogue to digital converter.

I've come across many odd faults with LCDs caused by low value and/or bad ESR electrolytic capacitors. Visually inspect all of them on the mainboard for bulging tops or leakage. Failing that, remove and test them.

You can sometimes discover if an electrolytic capacitor is the trouble by heating them with a hairdryer (don't roast them though!) and see if the fault clears or alters in some way.

Otherwise you may be looking at a faulty IC somewhere.

Incidentally, has the OSD failed to come up since shorting the IC pins? What are the numbers of the pins you shorted?

Why not tell us what brand and model set you have? Without some specific information it is hard to know if we can help.

Leonard

It's an Iiyama AS4636D 18inch LCD.

The OSD didn't come up even before I shorted the pins, so that's not the problem. I did visually inspect the board for any visible problems before doing anything and couldn't see any problems.

How would you suggest heating the capacitors without heating up everything else on the board also?

I'm not sure exactly the number of the pins, so I'll have to get the spec for the chip and compare that, I'll let you know.

I believe it was pins 6/7 or 7/8... not sure exactly with the small leads.

Also, upon closer inspection under a heat sink in the power supply there are two electrolytic capacitors that appear VERY SLIGHTLY bulged out at the top. Is there some way I can test these short of just replacing them and trying again? The bulge is very slight as I said... nothing I would have noticed had you not specifically mentioned that.

If they're definitely bulging they need replacement, it's as simple as that. This could well be the source of the original problem.

Dave

I use a hot-air station with small nozzle, whereas some just stick the tip of their soldering iron on the metal top of the cap for a few seconds, trouble with that is you can cook the cap quickly. One thing you could do is get some thick card and cut a small circle in it for the cap to go through, so it acts as a barrier to most of the heat. If heating the caps does nothing, heating the whole board can tell you if you have a bad joint somewhere... even surface-mount ICs can suffer dry joints, often invisible to the eye.

Here is the ICs datasheet, it's PDF and if you scroll through it, you'll find an image of it with all pins numbered:

You need a capacitance/ESR meter to test those slightly bulging caps really. If you don't have one, substitution is the only way, and probably a good idea if there is bulging present. Many bad caps don't bulge or leak though, just so you can bear that in mind with the rest of them.

Yes I do, I've built and sold many, very light, very inexpensive, utility racking but not for display in your kitchen. Post your Email and I'll send you a picture if you wish. jesse

On Sun, 05 Mar 2006 19:13:40 GMT, Jesse wrote: Sorry, posted to wrong group. jesse

Well, I replaced the two bulging caps with new ones, and unfortunately, nothing seems to have changed. Still can't get a picture or on-screen menu.

It'll be very interesting to know which pins you've been shorting to get it partly functioning...

Well, like I said, I believe it was pins 7/8 which is one of the color inputs and a voltage pin I believe.

I'm not exactly rushing to try repeatedly :)

Understandable.

Measure the voltage on pin 8, should have 3.3V there.

Yeah, it's 3.3V at pin 8.

Assuming the chip was getting input though, shouldn't the R,G,B in pins be at something (looks like between .5 and 1v from the spec). Because none of those pins have a voltage, so I'm guessing the problem is in getting the signal from the input to the chip. Although that doesn't explain why I can't get the onscreen display either.

Heat the top of the cap with the tip of a soldering iron until it gets hot, but not so hot it bursts! It will cosmetically damage the top of the cap, but don't worry about that.

Dave