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

[capthook]

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

All I could find in my parts bin was a 40uH ; of a higher voltage rating probably (it's bigger) ... and I'm a risk taker, so I swapped the stock inductor in the position that was getting hot obviously... it's been running for an hour now without shutting down. Just a band-aid on the situation, i'm sure -- since the IC INL858RN -- IS getting hot, maybe a short, thus overheating the inductor perhaps? The only diodes I can identify on the PCB are the larger black diodes, I think there's three , maybe 4 of those and they all test ok... the smaller stuff i'm not sure whats a diode, which is why I took the close up pics around that IC that is getting toasty... It's getting around 120F I think from what I can tell.

[budm]

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

The inductor for the boost converter will get really hot of the MOSFET is not switching on and off properly.

[capthook]

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

ok, good to know... Do you think the mosfet 9997GH above it could be the problem? or the one to it's right? One to the right of the IC is labeled MT1117 . Should I just remove and replace that guy ? It ran for 2 1/2 hours last night before I finally shut it off and went to bed -- so the larger inductor, whilst a bandaid did stop the display from shutting down. I just dont want to damage anything with the 40uH instead of 33uH in that position. Problem is that I cannot find a schematic for this board.

[capthook]

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

Also is TO-252 the same as 9997GH mosfet?

seems like the same one is also AP9997GH-HF ; 9997GH ; 9997CH....

[capthook]

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

http://www.datasheetspdf.com/PDF/9997GH-HF/774796/1

9997GH = N Channel Enhancement mode Power Mosfet
Drain Source Voltage = 100v ; 11A
R (Static Drain-Source On-Resistance) = 120m ohm / 200m ohm
Gate Threshold Voltage = 1-3v

TO-252 appears to be different... 60v i think

[cpt.charlie]

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

I would remove the coil and turn on the monitor, you won't have backlight but unless it has some kind of fault detection, you could determine with precision the cause of the reset.

The mosfet is controlled by the INL858RN i think the problem is caused by the chip, btw consider that this chip will get hot (it has a big ground at the bottom and the current of the leds flow thru this chip)

[capthook]

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

Ok, so maybe I should do that, test / observe pin voltages on the IC and on the mosfet after coil removal ? The IC gets hot... up to 110-120F I think , but not hot hot hot like the coil was (154F) ..

[capthook]

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

A better (large) photo of the PCB is attached ; it looks like perhaps a refurb? as that 330uH has obviously been replaced.

[srhofmann]

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

So on my board it seems as though it was IC502, between the two inductors, that was getting HOT. I had a little problem and ended up letting the sparks and smoke out of it. I didn't feel like changing the thermocouple to an non-conductive one and the bead slid off the IC onto the pins, thus leading to the sparks and smoke.

Could you do me a favor and let me know what markings yours has on it? I can't seem to read the markings that are left on mine.

Thanks.....

[capthook]

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

IC502 looks like: MP1484EN


MP1484EN-LF
Manufacturer:
Monolithic Power Systems (MPS)
Description:
Switching Voltage Regulators 3A, 18V, 340kHz Sync Step-Down DCDC

http://www.mouser.com/ProductDetail/...ZxUlxUkg%3D%3D

[srhofmann]

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

Capt.Hook,

Thanks. Looks like I shorted the output to ground. Hopefully it didn't take anything else out. Anybody want to bet shipping will be more than the device? Not gonna wait for a part from China.....

[srhofmann]

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

Looks like I'm not fixing this one. When I shorted out IC502 I managed to remove, think vaporize, some of the solder pads. On to the next project......

[capthook]

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

What a bummer. You can get the whole board apparently for around $22 /shipped from china (see link) I just wanted to solve the problem on the PCB instead of ordering the entire unit ; guess i'm gonna wait on some parts from our chinese friends here...

http://www.yoycart.com/Product/537360577727/

[srhofmann]

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

Thanks for the link. I was right it was more for shipping than the part. I really should have tried removing the blown out part before I ordered the replacement. Even with the 8 bucks for the unused MP1484 it's a grand total of 31 bucks to get a 27" monitor going.

[capthook]

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

Yeah not bad man... I ordered the parts (the IC, and the Mosfet) from china... willing to wait for it I have plenty of displays ; but if that doesn't work i'll just order the new populated board at that point. I noticed the connector at the top looks different, but I can always swap that ...2x mofets were $1.29, the IC was like $1.49 lol ... see this thread again in a month :-(

[capthook]

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

Ok, well it looks like my IC 502 is getting red hot too... I replaced the mosfet ; it didn't correct anything. So, I put my meter on the other IC I thought might be a problem but it wasn't getting super hot ; IC 502 was ... I'm starting to think this might be the flaw on these boards now. Unfortunately, I'd have to wait another MONTH for this IC... arghhh.... don't know what I am going to do yet -- I did order the MP1484EN ICs ; so I guess i'm still kind of determined to fix the board and not just throw my hat in and order the populated PCB

[capthook]

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

MP1484 = 3A, 18V, 340KHz Synchronous Rectified Step-Down Converter

The MP1484 is a monolithic synchronous buck
regulator. The device integrates top and bottom
85mΩ MOSFETS that provide 3A of continuous
load current over a wide operating input voltage
of 4.75V to 18V. Current mode control provides
fast transient response and cycle-by-cycle
current limit.

Ambient Operating Temp .............. –20°C to +85°C ;; 85c = 185F ... its getting to around 144-150F ...