Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

[capthook]

Ok, weird problem on my 27" Viewsonic ; model VX2753MH-LED. On HDMI, it works for about 4-5 minutes ; then resets to the viewsonic logo and does this over and over again. On VGA ; the display lasts much longer -- maybe an hour or more sometimes but then finally resets and does it frequently afterwords.

I can post pics ; there is one PCB board inside of the unit ; the one which 19v 3A power supply unit is connected. And a PCB above it connected with a wide ribbon cable ; I guess that's the display attachment / backlight inverter assembly or something...

1. Replaced all the caps on the video input board ; obviously just the large ones not the SMD caps and no difference.
2. Tested the (external) power supply ; and it's steady at 19v. Tested the board itself ; to see if it was getting 19v after the plug ; and it seems to be fine.
3. Tried running the display without the connector between the (backlight pcb?) and the video input board. Display turns on (white) ; does not turn off or reset ; so this does appear to be a problem with the input board.

On the board there are two 330uH coils ; I was thinking about replacing those next. Any ideas? I'd love to have this big display back in action

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Here's a picture of the video input board I am talking about .

[cpt.charlie]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Can you detect any overheating in the logic board? (raster chip and linear regulator specially)

[petehall347]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

have you tried regular tv ?

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Unit doesn't have regular TV input... I did notice a chip heating up on the board ; really hot... almost too hot to leave your finger on. Yeah, don't think it's a linear regulator , those are (3 pins one side, one on the other?)

[cpt.charlie]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Maybe the chip reaches a critical temperature and keeps resetting the monitor until you let it cool down.

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Thats what I am thinking.... I'll have to take the back off again and get the numbers off of the chip that's getting toasty...

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

If input / output capacitors to that chip are fluctuating in value.. can that cause overheating as well? ... or is that not as common as just a bad chip?

[cpt.charlie]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Are you talking about the SOT223 chip? linear regulators can oscillate under some circumstances (but seems to be uncommon)

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

I don't think it's one of the SOT223's getting hot... it's a chip, I'll have to open it again and grab the numbers off it ; thanks mate.

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Ok the overheating chip is INL858RN...labeled IC501 on the pcb. Should i just r&r this guy and see what happens? It's the chip with 24 pins closest to the two 330uH coils on the pcb. Temp rises much faster on HDMI input, as opposed to VGA.

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Ok, I thought it was the IC.. but it could be the 330uH coil (inductor) next to it, lol. I got out the laser temp gun, and one of the coils is going up to 140 F , whilst the other next to it sits at a comfy 80 F... no fluctuation. I'm going to replace that first and see what happens

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Ok, I swapped the coils ; and the coil still gets hot in that position . ... maybe the mosfet 9997GH / regulator before the coil? ...

I can watch the coil / inductor in that position using a known good 330uH rise to temps above 140-150F , which is when the monitor shuts off. This was heating up components around it, which threw me off initially.

Please see the attached pic, i've highlighted both parts I am referring to.

[srhofmann]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Perfect timing for this thread. I just put a new video card in a desktop and it's doing the exact same thing with the same Viewsonic monitor. The weird thing with mine is that if I use either hdmi input with a media player it doesn't seem to fail or at least I haven't seen it fail.

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Since you changed your video card - I wonder if your problem is related to the refresh rate ; did you change it to 60hz? tried multiple resolutions? ...

Mine does it with ALL devices... PS4 on HDMI, PC / Mac... doesn't seem to make any differece. It's definately hardware related on my end with this screen. The VGA input allows use for (hours) without problems. Use of HDMI inputs (either one doesn't seem to make a difference) heats up that 330uH coil really quick (saw it push 155 F last night) and then the display goes into a reset loop, or turns off. I'm going to dig into this further today... hopefully we can find a solution and not throw our huge 27" LCD monitors into the trash lol

[srhofmann]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Perfect timing for this thread. I just put a new video card in a desktop and it's doing the exact same thing with the same Viewsonic monitor. The weird thing with mine is that if I use either hdmi input with a media player it doesn't seem to fail or at least I haven't seen it fail.

Turns out I lied. Made it fail using the PC and then immediately tried a media player and it does fail. Haven't tried the VGA input but I'll throw something on it and try it. It definitely seems to be heat related because it ran for almost an hour this morning before it failed and now it's resetting/rebooting every few minutes. I guess it's time to open it up and take a look.

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Yeah, it sounds heat related like mine... on HDMI she'll last anywhere from 2 minutes - to under an hour. On the VGA input, much longer - sometimes almost 4, 5 hours or more without a problem. To be sure, I hit the same components with the heat gun to see if they were heating up as much on VGA ... they were, but it took much longer to get the heat numbers I was getting with HDMI hooked up.

The 9997GH mosfet seems to be Ok, staying cool and also supplying a voltage of 3.3v for something else ; it's input voltage is 19.2v from the 2x 150uF caps on it's left. I didn't take it off the pcb to test, but it seems like it isn't shorting my meter or burned up. Also to note : the top 330uH coil (one closest to the 10uF 100v cap, which is laying horizontal on the pcb) is supplied with that 19.2v ; and the lower coil is running at just above 5v. The one supplied with 5v stays at around 80-88F, never really running upwards in heat. The top one just gets hotter, and hotter until finally it shuts down. You can put your finger on this while it's running and feel the heat coming off of it. It won't shock you.

Also noted, the 100v 10uF laying horizontally is supplying 40v to the panel. I wondered at one point if the heat issue is normal on the coils ; but it doesn't seem likely to me because it gets really hot.

[cpt.charlie]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

I can't find any datasheet about the INL858RN is it some kind of led driver? what is the input voltage of the monitor? the chip could be a copy of the OZ9899.

Check nearby diodes.

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

Input voltage is 19v, 3.42A ... The inl858rn i believe is an LED inverter controller ic... it however doesn't seem to be heating up ; just the inductor... I noticed a russian and then another chinese supplier for the board, and that specific inductor had been replaced with a different 330uH inductor ..?.. But; logic says 95% of the time the inductor isn't the problem it's somewhere else; like to high of a voltage to the inductor itself. Plus I swapped them and the one that wasn't overheating in the other position started overheating in it's new position.

We're talking 150 F , after a short period of time. Pretty hot.

The top one that is getting hot is running @ 19.2 v, and the lower one around 5.2v... I'm wondering what controls the voltage to this top inductor... is it the mosfet above it? There is also a diode in line before that mosfet ... I feel like we're close ; wish I had some mosfets , the diode and the IC to just swap em out and see what happens, but because I have multiple displays I can wait and try to find the culprit with some guidance here...

Should I check / watch pin voltages on the IC to make sure they are within range (see pic)

Or should I investigate this overheating coil / inductor first? ... I'm thinking the later...

The datasheet for this IC isn't complete ; but here's what I found : http://www.datasheetq.com/search.jsp?q=INL858RN

[capthook]

Re: Viewsonic 27" LCD turns off after a while -- longer on VGA, Shorter on HDMI?

correction ... I think these are 33uH ; thus a "330" inductor...