iiyama ProLite X486S dead - psu / inverter issue

[jetadm123]

Re: iiyama ProLite X486S dead - psu / inverter issue

The 4 mosfets you checked appear to be good.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Yep, it turns out I was using the wrong screw (actually AC inlet ground screw, so that's why it did not work).

New measurements:
* everything unplugged, even backlight, board in AC power 240V:
- all pins fluctuate around 0V (-0.14 <-> +0.14)

* monitor logic board connected, everything else disconnected (panel, backlight), board in power - monitor OFF - now high frequency noise is immediately heard after plugging in.
- pin 1 => 0V
- pin 2 => 3.15V
- pin 3 => 5.09V
- pin 4 => 5.09V
- pin 5 => 0V
- pin 6 => 0V
- pin 11 => 0V
- pin 12 => 11.94V

* logic board connected, everything else disconnected, monitor in standby
- pin 1 => 0V
- pin 2 => 3.15V
- pin 3 => 5.09V
- pin 4 => 5.09V
- pin 5 => 0V
- pin 6 => 0V
- pin 11 => 0V
- pin 12 => 11.94V
(the same reading)

- monitor ON [only logic board connected] - faint blue led shines
- pin 1 => 3.99V
- pin 2 => 3.17V
- pin 3 => 5.09V
- pin 4 => 5.09V
- pin 5 => 0V
- pin 6 => 0V
- pin 11 => 0V
- pin 12 => 11.97V
(almost the same reading, higher voltages [a litttle] on 12V and 3.3V line, 5V line unchanged, voltage 4V on pin 1 - ON/OFF)

* everything connected, monitor ON - faint blue led shines
- pin 1 => 3.95V
- pin 2 => 3.14V
- pin 3 => 5.07V
- pin 4 => 5.07V
- pin 5 => 0V
- pin 6 => 0V
- pin 11 => 0V
- pin 12 => 13.04V

So the whole point why 4 volts dropped was because I measured it incorrectly. I'm sorry about that Now it seems the power board is in excellent condition.

[jetadm123]

Re: iiyama ProLite X486S dead - psu / inverter issue

At this point, I would move over to the logic (main) board and measure the outputs of the two voltage regulators U901 and U902. Again, use a mounting screw for your ground probe. Measure all 3 pins and report your findings.

[retiredcaps]

Re: iiyama ProLite X486S dead - psu / inverter issue

Yep, it turns out I was using the wrong screw (actually AC inlet ground screw, so that's why it did not work).

Whenever I see negative voltages I know that the wrong ground is being used. Although, I could do "relative" math and figure it all out, I would rather have the "proper" positive readings.

Remember there is the hot and cold side. Each has its own ground. When measuring the cold side, use cold ground.

edit: The big white thick line on the underside of the PCB shows the separation between hot and cold.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

* With monitor ON (blue led - faint)
U901 pin 1 => 0V [also short with ground]
U901 pin 2 => 1.79V
U901 pin 3 => 3.83V

U902 pin 1 => 0V [also short with ground]
U902 pin 2 => 3.29V
U902 pin 3 => 4.65V

* With monitor in standby (orange light)
U901 pin 1 => 0V [also short with ground]
U901 pin 2 => 1.79V
U901 pin 3 => 4.09V

U902 pin 1 => 0V [also short with ground]
U902 pin 2 => 3.29V
U902 pin 3 => 4.79V

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

retiredcaps - thanks for explaining. I never knew what that line was for. I'm not familiar with the terminology though, English is not my native language (as you can definitely tell), so I just assume hot is +12V side and cold is ground side (or does this have something to do with AC/DC "sides")?

Anyway, from the information you gave, I'm not sure if I measured the 12 pin connector correctly, again. I measured it using the ground shown in the attachment. The ground screw that I used is on the other side of the "line" the connector is.

[jetadm123]

Re: iiyama ProLite X486S dead - psu / inverter issue

* With monitor ON (blue led - faint)
U901 pin 1 => 0V [also short with ground]
U901 pin 2 => 1.79V
U901 pin 3 => 3.83V

U902 pin 1 => 0V [also short with ground]
U902 pin 2 => 3.29V
U902 pin 3 => 4.65V

* With monitor in standby (orange light)
U901 pin 1 => 0V [also short with ground]
U901 pin 2 => 1.79V
U901 pin 3 => 4.09V

U902 pin 1 => 0V [also short with ground]
U902 pin 2 => 3.29V
U902 pin 3 => 4.79V

The U901 and U902 output voltages look good. At this point, I'm pretty much out of ideas.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Me too. How does the backlight turn on? Maybe we can benefit from the fact that there's no backlight no display, simply nothing. Maybe I can measure voltages going to the panel or the backlight, but how? And the question is would it help? Personally, I don't think it's a problem with the power board anymore. Too bad I don't have a spare logic board to test it with. I'd also replace the capacitors but if they are not the problem, then it's pointless.

Another idea that comes to mind is to desolder some parts to get proper readings. For example two transistors on the power board have pin 1 and 3 soldered to the same PCB lead, so I can't measure them for shorts that way. But then again, the power board seems to be OK. IF there should be 0V on pins 5 and 6 in all cases (which there are, but I don't know whether it is normal or not).

What could be the problem that even the backlight or LCD does not turn on? Is this all controlled by the logic board?

[selldoor]

Re: iiyama ProLite X486S dead - psu / inverter issue

selldoor - My TK capacitors are not like that. They have a "TK" mark in circle and are blue. And the other ones - they are "samwha". So goes the capacitor quality at my local store Maybe that's why the LG adapter burned out a week later.

I have also tested all four Q's on the back site of the board with my multimeter set to "200" - resistance. I almost never got any reading, always just a bright flash and then immediately "out of range". I tested the 8-pin Q's by getting one lead on one leg on side A and other lead through all legs on side B. Then I moved the lead on leg 2 on side A and repeated the process. Therefore, I tested all possible combinations. I also tested the legs in all possible combinations on one side of the 8-leg transistor - same results. The other side legs were always soldered to the same PCB lead, so measuring there did show 0.1ohm resistance.

While I was measuring I checked the big transistor near big capacitor - setting 200 - never got any reading (out of range). Also tested with short circuit tester - did beep once for a very small split of a second - after that the resistance started to rise until out of range.

Other two "smaller" transistors - the same, except on one of them I can get a reading of ~94 ohms between pins 1 and 2 (pins 3 and 2 - out of range). The other one - always initial ~120 ohms, then jumps to out of range. On these two, pins 1 and 3 are soldered onto the same PCB lead.

Hope this helps. These readings do not tell me much at all

AAARGHHH!!!! I think you my have gone horribly wrong
with my multimeter set to "200" - resistance. I almost never got any reading, always just a bright flash and then immediately "out of range"

May have got lost in translation but you NEVER measure resistance with the power ON. When you say bright flash do you mean sparks on the probes?

This may have caused some damage - you will have to retest them if you had the power on.

I think it would be wise not to do unspecified testing as you could do more damage and possibly to yourself. For example

While I was measuring I checked the big transistor near big capacitor - Was the power on while you did this ? The transister would probably be at the same high voltage as the Cap - 325 volts!!!

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

"May have got lost in translation but you NEVER measure resistance with the power ON. When you say bright flash do you mean sparks on the probes?"

No, the power was off. I meant "a bright flash of measurement" on the multimeter display. So that I saw a measurement of say 120 ohms and then out of range. Let's say the multimeter display refresh rate is 0.3 seconds so I saw 120 ohms for 0.3 seconds, then out of range. Means the transistor was "starting" or something like that, but definitely not shorted.

No worries - power definitely off until said otherwise ;-)

"While I was measuring I checked the big transistor near big capacitor - Was the power on while you did this ?"
- nope, all off. I only tested the big capacitor itself and connector voltage + main board regulator voltage while in power outlet.

[jetadm123]

Re: iiyama ProLite X486S dead - psu / inverter issue

Since your power supply supply is outputting 12v to power the inverter section, I would at least expect to see a short flash of light on the screen when you first power up the monitor. You can check to see if there is a blown fuse on the power board leading up to the inverter section. Try shining a flashlight at an angle on the screen to see if you can see a faint image. If you see nothing, then I would suspect the logic board.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Interesting experiments I've made. previously I stated that the display does not display anything and there is absolutely no backlight. While that's true, I now shined on it in complete darkness using desktop lamp (60W light bulb). I'm now certain that when the monitor is ON, the screen becomes crystal clear BLACK. When in standby or OFF, the light is so strong, that I can see the screen in like "dark grey" color. Once turned on, it becomes black. On standby (~10 sec), it becomes "powered off" again - "dark grey".

Does this mean anything?

EDIT: I've also watched the screen in complete darkness, and there is absolutely no visible backlight action by the human eye.
EDIT2: There is certainly nothing displayed on the screen.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Oh my god, redo that!! There is a no signal message displaying on the screen but it pops up more than 3 seconds late and I've missed it! How can I be so blind!!! I mean my eyes are not the best but I should catch this MUCH earlier on! I guess I thought that those messagess would be MUCH more clearly visible using flashlight, but I was wrong ;-) This is a true moment of joy for me, sorry for misleading you guys! So this monitor has ONLY problem with backlight! This makes me very happy ) So back to the power board then, I'm going to check some "2 secs to black" topics even though that's not the exact case here ;-)

[selldoor]

Re: iiyama ProLite X486S dead - psu / inverter issue

Good - was lost in translation. Do you still have the old screen you mentioned, the one that burnt out? If so perhaps you can use the panel
to test the back light circuits. You could try connecting to this one
and see if you get a flash at least. I use an old smashed laptop screen for this.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Unfortunately I currently use the old screen. It's working (LG1960TR), only the adapter did burn out. I'm now using a notebook universal adapter set to 15V/3.5A with 3x 6A diodes in series on it's output to power the screen (results in 12.02V). So I can't use it to test the backlight, because then I have no screen.

I have now tested the F901 main fuse - shorted - 0ohms - OK. I also found one more presumably fuse, FB901, also shorted, 0 ohms, OK.

[jetadm123]

Re: iiyama ProLite X486S dead - psu / inverter issue

The schematic shows a inverter fuse, F902. Try looking for it. It may or may not exist on your power board, since you have a different revision of the board. If you can't locate it, then pin 3 of each P3503QVG is connected to 12V. You only need to make one measurement because if you don't see the 12V, then you'll have to trace backwards to see why you are not seeing it.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

I checked the fuse F902, found it, OK (shorted).

I'm looking at the TOSHIBA LCD-AD174TW service manual, page 41, section
2.) W / LED , No Backlight

The first step is "Check C928(+) =12V". I think this is a mistake. The word C928 does not appear nowhere else in the document. I can only locate C926, C927 and C929, and those 3 are listed on page 57.

So I have checked the C929 + and it's only 3.8V on one side and 2.48V on the other. Not 12V. Also the backlight is disconnected in this test, because the C929 is on the backside of the power board and the cables are not long enough. Logic board is connected though.

I'm going to test one of P3503QVG and see what happens.

EDIT: also, the power board itself is not connected to any ground with any screw. I don't know how, because as I said, C929 and P3503QVG's are on the back side of the board, and when screwed down, I can't get to them. Don't know wheter this is an issue or not. Logic board is gounded with screws and connected to power board.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Q209: if pin 1 is the one marked with a small dot, pin 2 is the opposite one, and pin 3 is the next one on the opposite side (in other words pin 3 is right next to pin 1), then that pin has -0.01V.

Please tell me if I can measure this with the backlight disconnected.

[selldoor]

Re: iiyama ProLite X486S dead - psu / inverter issue

Off current thinking but can you look at Q901 - it looks like a solder blob but is shaped
like the Q902 transistor - has it been snapped off or is it just solder? The schematic whilst a guide has a few differences It has Q901 mentioned in the parts list but cant see it anywhere else.


Hah - found a pic with it on???

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

The Q901 is in normal state, present and is black - on the photo it must be some camera weirdness. It really looks like a blob of solder but you can see it more clearly on photo 4 - also attached here.