Iiyama monitor PL2483H - No LED Backlight.

[Turnip]

Hi Folks,

Have this one in where initial OSG is visible with a torch. Set doesn't cut to S/by, but no other display as didn't bother try any input.

Checked usual diodes and caps finding no problem, suspect screen LEDs.

With a CCFL monitor it's a doddle to check tubes, but this one has a plug with 6 wires the screen, whereas most have just a couple.

Checked around, and no info about LED failure on this monitor, or anything else.

Wonder if anyone has sorted this problem - Thanks - Chris.

[Davy]

Hi Turnip

I'd be treating it like LCD telly inverter or no supply to inverter the leddy's..... the LEDs are usually ran in banks and driven from a inverter.... that *may* be hidden under the screen where the CCFL's are usually parked.

I'll stick mi neck out and bet they won't ALL be ran together Chrimbo tree style or paralleled. I have a IIyama CRT monitor.... that keeps working working and working, usually highly rated IIyama are.

The LED's could give trouble..... I doubt this is the fault though, unusual for them all to be out I'd say.

Dave

[downunder]

Hi Chris,

Some activity on quuq at last! I thought it might have slid into an abyss.

As Dave points out, the panel LEDs are arranged in strings, irrespective of whether they're mounted top and bottom, left and right sides, or in an array (scattered throughout the back). The last is probably the easiest to fix, but the arrangement of the LEDs is a Midsummer Murder mystery until you crack open the panel to access the LED cavity, something I relish doing just for the Halibut.

Sounds like your LED Driver is part of your PSU and 6 wires into the panel means 3 voltages in to the LED strips and 3 return wires where failure detection is normally facilitated. Failure of just one LED, because they're in series, will cause the micro to shut down all LEDs. On said plug, the LED Driver should generate 3 voltages, not necessarily the same, but of the order of 75V to 150V, depending on # of LEDs per string.

With the panel apart, you can spot any burnt out or heat-stressed LED or joins, and you can isolate each string, and using a current-limited variable bench power supply, you can see if each string lights up. Start with low volts and wind it up slowly until the LEDs ignite with low illumination. Don't copy my first effort and start on "surmised voltage", destroying a LED string.

Bruce Chapter XXII, Verse XLIV

[Turnip]

Thanks, Davy and Bruce,

My first LED back-light failure so naturally reluctant to come to a premature conclusion.

Otherwise - Simply ignorance. Suspected however that any functioning string would give a brief flash B4 set cut to S/by, but with this one - Nothing at all.

Hi Bruce, will wind them up slowly, but they're just top and bottom jobbies, as most small monitors are.

Enjoyed Chapter and Verse, as guess Quuq folks will - Love your Latin, but a bit dubious, as suspect It's Australia, where folks only came together recently - Chris

[downunder]

Hi Chris,

Strangely nuff, LED backlight don't seem to give the momentary flash that CCFLs do. Top and bottom jobbies......these can be dicey as the individual LED terminals can be impossible to get at, but if you do succeed in getting access to a crook LED, you can bodge it by substituting a reverse biased 3.6V zener.

Bon chance, and don't knock the Latin.....I studied it at school, and a fat lot of good it did me....don't think they use it any more.

Bruce

[Turnip]

Hi Bruce,

Thanks for the zener tip, was fortunate this time as noticed L801 (between the 2 electros in the LED supply was dry jointed, soldered by only one pin using pressure to make contact on the other)

Recently bought 'Idiots guide to Latin' and in retirement might well read it - Chris.

[downunder]

Hi Chris,

Statistics suggest the average family has 1.5 children.....might explain why there are so many halfwits in the world.

Bruce

(reference: The Wizard of Id)

[Turnip]

Hi Bruce,

Will go check that one. Knew the one with 'Toto' where self confidence wins out despite the wicked witch of the West - Wonder why 'West', as West is sort'a nice, and was even then, though not terribly Socialist.

Mind you, our Obama is trying do a fine job in his last few days before money takes over again.

Confused as ever, being the last child in a quorum (of four) - Latin again, can't beat it - Chris.

Checked the reference - Was into 'Fuzzy Freaks' at the time, as they were simpler.

[Davy]

One of them groups of wires Bruce mentioned in a post or two back, one will be a PWM control for the brightness, t'other will be a ground and a +ve.... there are time they may double the ground and +ve leads to improve current handling. As far as I know one of them will be a on/off control, so that leaves two more wires if I'm on the ball.

The combination is huge when it comes to LED's, psu inverter or separate inverter,  the telly I did had led strips around the top and sides with the inverter inside the actual screen... I can't recall how many wires I had, it was more than two for sure going inside the display.

The flash you see when CCFL's strike is the gas ionizing and stabilizing isn't it something they all do, the start up voltage will be much higher at 'switch on' then will drop to the running voltage once lit unlike a LED.

Dave

[Turnip]

Hi Davy,

Nice one, and thanks - Thought LED back-lights would be a doddle, bit like Crimble lights where you had to find the duff LED and change it, or maybe fit a zener diode if you hadn't got one.

Guess not so simple, but natch thought the inverter would have a brief go before going for safety - Many thanks for the Heads up - Chris.

[Davy]

You are right in a sense Chris, they won't all be in series, there's many combination's consider crimbo tree lights split up into banks of four, the banks would run in parallel, ok this would reduce the voltage but at the cost of doubling the current.

I seem to recall the LED voltage to the LED banks was around 8V while the voltage to run the inverter was around 24V from the main power supply, don't take me 100% on this. I was kinda gobsmacked when I saw the LED inverter....... no more than about an inch high, very slim line indeed.

But as said there's many, many combination's, some may well have the LED voltage derived from the main power supply. Don't ask me why they tuck it under the LED housing sounds stupid to me, the only reason I can think of is RFI screening, my way of thinking is get a bank of low voltage LEDS and the current increases as the number increase's and so does the electromagnetic radiation.

In my case they looked like them LED strips you can buy, just stuck round the edges.... I guess their colour temperature and current consumption are tightly matched.

Dave

[Turnip]

Hi Davy and thanks,

Mine was sorted with a P/S jobby, as noted - Chris.

[Davy]

Goodun, glad it's working.... good monitors them Iiyama's.
I have a HM703 crt  un it just keeps going, going and going. I replaced a couple of swollen caps years back although it still worked fine, did the dry joints which I understand this one is noted for but the Diamondtron CRT far superior and sharper than my LCD monitor I reckon..... the only time it's off is at beddy, beddy bytime.

Cheers, Dave

[Turnip]

Hi Dave,

Use a couple of 'Sammy 24 LCD' myself as can't see anything smaller these days. The CCFL one I need to fire up five minutes B4 I look, as it's initially a bit dark, The LED one has a sort of bleed through, but is incredibly bright, right from kick off.

Not seen a CRT monitor since the last century, when used to get them from the Council tip - Chris.

[Davy]

Dim piccy *could*  be the cfls.... the 'whites' usually show discoloration when this happens.

Wondering if the over bright leddy screen is causing bleed through, does contrast and brightness alter any, how about scoping and finding the PWM pulse to the LED drivers.... not only will there be a brightness control there may be a back light brightness setting, me be tempted to set everything to default in case someones been 'fiddling'.

I have come across a telly anything can be adjusted WAS adjusted, nothing was left untouched, the real reason for the fiddling was the sound was awful........  granny's wind up gramophone with steel needle sounded better..... pick up must've weighed like a bag o' spuds.

Dave