Iiyama prolite 1900s dead

[bluebear]

Hi!

My LCD turned dead tragically with a burning smell, just like that. Black screen, the on light steady green.Pushing on off buttton does not turn lcd off, nor will it turn the green diode to orange. The screen always stays black.

I was certain to find some badcaps when I opened it up. At least some burnt electronics, but found nothing. It looks ok. See photos. Caps are Hermei and elite. Checked esr and all seems well on the powerboard.

I have measured the voltage at VRM on the logic-board, and had 3.3v. Seems alright since the diode on the front is glowing. Caps are lelon and one hermei.
Checked esr and 3 lelon 47uf is shorted so a replacement might be the cure.
Could one of these caps have emitted the burnt smell that I felt?

Any pointer would be appreciated, but I do believe it to be a lost cause. However, it might not.

[jetadm123]

Re: Iiyama prolite 1900s dead

Try replacing the cap(s) first, if you think that might be the problem. The cap would have most likely burst open if you smelled something burning.

I would then start with the basic voltage output checks. Sounds like the 5V output is working as evident by the logic board getting voltage. Try checking for the 12V output. You can try checking for it on the wiring harness. If not there, then it will at the output of one of the heatsinked devices (probably on the left side of the board with the cover with 2 screws holding it to the heatsink). Also, with a flashlight held at an angle to the screen, check to see if you can see an image.

[kc8adu]

Re: Iiyama prolite 1900s dead

get a closeup of those 2 soic-8 mosfets under the inverter transformers.

[mockingbird]

Re: Iiyama prolite 1900s dead

Is it my imagination or are those brown Hermei caps on the left using a Panasonic style vent indentation? Tsk tsk tsk Hermei.

[meanderer]

Re: Iiyama prolite 1900s dead

caps don't give off burning smells, at least I haven't seen one yet.
I would check the transistors first.

[bluebear]

Re: Iiyama prolite 1900s dead

Hi and thanks for all your advise! Much appreciated.

I de-soldered the small 10uF Lelon on the logic-board only to find out
that they were ok. If I had looked more closely I would have seen the tiny smd resistors on the front side, thats why they where shorted.

@ jetadm123
Checked for voltage in the harness near the big heatsink. Found 12 and 5v.
12v: 11.25 (measured with no load)
5v: 5.14 (measured with no load)
They seem ok.

@ kc8adu & meanderer
The mosfets are labeled stm6930a, found the datasheet attached here.
Now I only have to figure out how to measure them. Any suggestion would be great.

[retiredcaps]

Re: Iiyama prolite 1900s dead

Now I only have to figure out how to measure them. Any suggestion would be great.

Put your multimeter on 200 ohms if manual ranging. You can test this "in circuit".

Test for shorts by measuring D1-S1, S1-G1, D1-G1, D2-S2, S2-G2, and D2-G2.

Any reading less 30 ohms suggests a short.

[bluebear]

Re: Iiyama prolite 1900s dead

Thank you retiredcaps.

Measured as described.
None where under 30 Ohm. More in the 1000 Ohm region.
So i guess they are alright

[retiredcaps]

Re: Iiyama prolite 1900s dead

Also, with a flashlight held at an angle to the screen, check to see if you can see an image.

Did we get an answer for this?

[bluebear]

Re: Iiyama prolite 1900s dead

Did we get an answer for this?

Yes... but I must have forgotten to write it down.
I cant see anything with a flashlight on the screen.

[retiredcaps]

Re: Iiyama prolite 1900s dead

On the top side of the power supply, there are 4 transistors. I think they are Q901, Q907, Q909, and Q90? (marked B C E).

They are loacted all above the left hand inverter transformer.

Test all 4 for shorts. B-C, B-E, C-E. Again, any reading less than 30 ohms suggests a shorted transistor.

[bluebear]

Re: Iiyama prolite 1900s dead

Checked all four and all checked out.
Hmmm.

[retiredcaps]

Re: Iiyama prolite 1900s dead

Your photo isn't close to 2000x2000 resolution (the max supported on this board) and it is hard to tell, but look for a picofuse on your board. It is usually marked PFxxx. It might be underneath the shield or on the backside?

[bluebear]

Re: Iiyama prolite 1900s dead

Scanned the board for a picofuse, but I cannot find any. Perhaps I have looked at it for too long. I will call it a night. Thanks again for your advise retiredcaps.

Edit:
I found one that could be the "picofuse". Its located under the shield close to small coil. Its labeled F802 (F801 is the ordinary fuse at ac input), but its an bridged joint and not a fuse at all.

[jetadm123]

Re: Iiyama prolite 1900s dead

Yes... but I must have forgotten to write it down.
I cant see anything with a flashlight on the screen.

Since you're getting 5V and 12V output from the power board , but no image on screen, try checking the output of the voltage regulator (I104?) on the logic board. Looks to be stamped 1084-33?, where the 33 should equal 3.3V. Also, look closely for any surface mount fuses that may be on the logic board.

Also consider checking the secondaries of the inverter transformers. With power off and monitor unplugged try taking resistance measurements across the points marked. Note: The points I circled are the best I could do because of the photo quality. Please verify those points before checking.

[bluebear]

Re: Iiyama prolite 1900s dead

I attached larger photos, maybe that helps.
I measured at the position you suggested jetadm123.
From left to right on the left side: 2.964 and 4.64 MOhm
Right side going clockwise: 2.969 and 3.92 M Ohm

I will check the vrm.

[retiredcaps]

Re: Iiyama prolite 1900s dead

I cant see anything with a flashlight on the screen.

This is with a computer hooked up to it?

[jetadm123]

Re: Iiyama prolite 1900s dead

I attached larger photos, maybe that helps.
I measured at the position you suggested jetadm123.
From left to right on the left side: 2.964 and 4.64 MOhm
Right side going clockwise: 2.969 and 3.92 M Ohm

I will check the vrm.

Yeah, I must have given you the wrong points to check, since I was expecting something around 950 ohms.

[bluebear]

Re: Iiyama prolite 1900s dead

Right, the VRM is ok. Input voltage is 4.7V and output 3.349V.

Quote:
Originally Posted by bluebear
I cant see anything with a flashlight on the screen.
This is with a computer hooked up to it?

Nope, I was looking for the no signal sign.

[retiredcaps]

Re: Iiyama prolite 1900s dead

Nope, I was looking for the no signal sign.

Sometimes the no signal sign is small or moves around and easily missed without a backlight.

Using a computer for display, you can look for your favorite desktop display/background.

It also helps if you are in a dark room to verify.