LG monitor PSU? oddity/query

I have never had a problem with a PSU and a monitor. Are you sure it is not the monitor that is at fault, or incompatible? I once had a problem with a printer and PSU where the issue was that the PSU was underpowered. Using the correct PSU resolved the problem.

Jethro_uk <jethro snipped-for-privacy@hotmailbin.com wrote in news:vb99fk$3pm44$ snipped-for-privacy@dont-email.me:

1. You have a fault that does not disappear on a psu change.
2. The psu powers other known good monitors successfully.

Conclusion: You have a faulty monitor.

Well it's been working for 4 months. I have 2 HDMI outputs on the laptop, and the good monitor will show both.

But I can only relate my experience in managing IT kit - that PSUs are the primary suspect in cases like this and replacing them has always worked.

But in this case, even a known "good" PSU seems not to work. And the ones that don't work with the dud monitor do seem to work with the good one.

I was curious as to whether the dud "monitor" by some chance needs that tiny - but within spec - extra bit of juice for no reason.

I had a brand new TV from currys that did a similar trick. It was fine as a TV, but the moment I wanted it to uses its Ethernet, it switched itself off. I took it back, but having no Ethernet they couldn't reproduce the fault in store, and didn't want to replace it. I said 'Look. I am not returning it for money, I am not wanting a different TV, I just want exactly the same TV as this, just one that works. Why would I do that if it was not faulty?'

They gave me a new one and its been flawless ever since.

So it is entirely possible that you have a monitor that overloads the power supply due to something that could be as simple as a failed capacitor.

Whether you want to delve into its innards or simply bin it, is up to you.

It is extremely possible. See my earlier post. In many cases those that like to fix such, go hunting with thermal cameras and volt and resistance meters to see what component is drawing ,more than it should. But is it worth all that time and effort to YOU?

Id open it up and look for bulging capacitors, but that is really as far as I would go.

I've just fixed (touch wood) a Philips BDM4065UC. I picked up a spare with a broken panel from ebay and have been swapping bits.

Symptom was the monitor would run fine for maybe half an hour, then there'd be a loud click and the screen would go off. Turn it off at the mains, turn it on, screen would come back. But then click and go off after maybe a minute. Repeat and now it did it after 30 seconds.

I suspected the PSU, so pulled the board. No obvious bulging caps, swapped it with the spare. Problem still there. Next I pulled the controller board (with all the HDMI inputs etc). No obvious bulging caps or similar damage. Swapped it over and that fixed it (thus far)

Given the way the fault recurred more and more often, I suspected something thermal related. The SoC is under a metal heatsink which is soldered to the board, and there's not much else on that board. My working theory is that the thermal paste under there has dried out and so the SoC is overheating. By swapping it, presumably the replacement has better thermal paste.

It's working now, so I'm not planning on testing this theory out unless I have to take it apart again, but will do if necessary.

About a decade ago we had a similar fault (display corruption rather than shutoff) on the ASIC (Altera hardened-FPGA) some Samsung 30" monitors, where the solution was to drill a lot of ventilation holes above the chip to cool it better.

So thermals are also something to consider.

Theo

Thanks for the replies all.

Symptoms have now settled down to:

Turn on monitor. There is a brief flash of backlight where you can see the content, then nada.

PC however still thinks the monitor is there & connected (so you can hilariously "lose" windows).

Am concurring it's a faulty capacitor on the monitor itself :( Need to find a way to open the beast and visually inspect. And then rue the say the local hobbiest shops disappeared as it's £5.00 for a 5p capacitor + £4.95 P&P :)

Mmm. That suggest that in fact it is simply the backlight PSU that has gone. Ive got a monitor that has massive hum bars across it like that. There may well be 3 fluorescent tubes needing a high voltage. And a PSU that is no longer capable of supplying it.

Likely a chip, a power MOSFET and some caps and inductors

Only if you buy from RS etc. Ebay is the place to go. Loads of people on the dole buying up old stock from the days when we made stuff, popping it in an envelope and making

I've even had stuff from France and Germany cheaper than Farnell or RS

Just don't buy chinese *components* from China. It's all sinclair radionics s*it rebadged rejects.

That is pointing towards junking the monitor :(

Annoying as I like them in pairs. Also - despite it have stuff al value 9 years after manufacture, I can't find one anywhere.

It is probably worth opening it up and looking for something obvious like a bulging 200V electrolytic.

The behaviour suggests its right on the edge of being OK but draws enough power to shut down the PSU.

Id guess at something on the secondary side of the PSU that feeds the fluoro tubes. Probably the main smoother cap.

a cursory inspection doesn't find anything obvious, then bin it

Yes. I've got more than a few old monitors that work fine, or have trivial faults, but are simply *obsolete*.

How?

Its an SMD.

But the little stubs of wire under the capacitor stick out a millimetre or so each side. As long as you don't mind melting the plastic base, there's more than enough to get an iron tip on, and the PCB pad extends beyond the terminal all round.

If that is the case, then yes, its possible

That suggests to me, that the backlight has simply failed, rather than the entire monitor switching off. Can you not see anything on the screen, despite the lack of backlighting?