Dell 1905FP Won't Turn On

[obscurehero]

Re: Dell 1905FP Won't Turn On

while I don't have the IPS (I think I called it a "PSU" board before, oops!) board in front of me right now, I think my board is a later or earlier version without the 22uF v 2.2uF cap problem. I ordered the 22 because toast suggested it, and I thought maybe I missed it however I did have TWO 2.2uF cap's when I surveyed the board.

I actually thought that maybe the 22uF might be on the other board (the display board?) and I hadn't checked that board yet. I'll double check now that you've mentioned it however!!

[obscurehero]

Re: Dell 1905FP Won't Turn On

A quick explanation of the specs.

uF is a nominal value. Actual value is usually within 20% of nominal. Voltage is the maximum design voltage. If you exceed the design voltage endurance specs are not guaranteed.

Temp is for rating purposes, it's combined with the endurance. In other words, a cap rated for 4000 hours at 105°C is expected to be within 20% of rated capacitance after operating at or below the spec'd ripple current for 4000 hours at 105°C. ESR is a 'better than' spec. The ESR is guaranteed to be below 55 milliohms after operating for 4000 hours etc.

In actual practice, the ESR of new caps (Capxon, Panasonic, and other brands) are always well below their rated ESR when new. The precise details have escaped me, but I measured the ESR of some new caps that were rated at .06 ohms. They read .02 - .03 ohms. I also measure some caps that had been in use for two years. Most of them also read .02 - .03 ohms. Except for some that had 'popped' that read .5 ohms or greater.

PlainBill

THIS^^ was very helpful to me. I appreciate you breaking it down for me. I had checked the FAQ section and I didn't see a clear explanation.

Thanks Bill!!

[Lumberjack777]

Re: Dell 1905FP Won't Turn On

while I don't have the IPS (I think I called it a "PSU" board before, oops!) board in front of me right now, I think my board is a later or earlier version without the 22uF v 2.2uF cap problem. I ordered the 22 because toast suggested it, and I thought maybe I missed it however I did have TWO 2.2uF cap's when I surveyed the board.

I actually thought that maybe the 22uF might be on the other board (the display board?) and I hadn't checked that board yet. I'll double check now that you've mentioned it however!!

I just call it an IPS board for inverter - power supply. But anyways, when I had that problem I ordered a new one from my supplier. It lasted 6 hours. I called him the next day and he sent out another one. I wanted to find out why the previous board burned out so fast. I finally narrowed it down to the 22uf 50v cap, because those two caps need to be identical. Since the 22uf cap was the same side of the board that burned out both times previous. I deduced that the 2.2uf 50v cap was the good one. I popped in the 2.2uf 50v in place of the 22uf 50v and it has been working great ever since. Though I also had to replace the inverter transformer because it got taken out both times by the improper 22uf 50v cap. I contacted my supplier and he agreed, and said he was replacing the 22uf cap on 4000 boards in stock. :^

[obscurehero]

Re: Dell 1905FP Won't Turn On

I just call it an IPS board for inverter - power supply. But anyways, when I had that problem I ordered a new one from my supplier. It lasted 6 hours. I called him the next day and he sent out another one. I wanted to find out why the previous board burned out so fast. I finally narrowed it down to the 22uf 50v cap, because those two caps need to be identical. Since the 22uf cap was the same side of the board that burned out both times previous. I deduced that the 2.2uf 50v cap was the good one. I popped in the 2.2uf 50v in place of the 22uf 50v and it has been working great ever since. Though I also had to replace the inverter transformer because it got taken out both times by the improper 22uf 50v cap. I contacted my supplier and he agreed, and said he was replacing the 22uf cap on 4000 boards in stock. :^

The board is at work (I'll likely replace the caps there, as it has better ventilation than my row-house apartment), so I'll check it on monday and get back to you. I wouldn't mind if it never had the 22uF cap problem!

[obscurehero]

Re: Dell 1905FP Won't Turn On

nope. Checked the board, and it has one 2.2uF and one 220uF capacitor for each transformer. I guess I dodged the bullet on that one.

[Toasty]

Re: Dell 1905FP Won't Turn On

So, you ordered 2 - 2.2uF and 1 - 22uF, correct. That means you'll have the 22uF left over.

On the back of the board in that area, can you take a clear "macro shot" of the circuitry. If you get it from the inside pins of both transformers. I have a shot but it is not clear enough to discern the traces. Also, can you report the numbers line by line on the 8 leg SMD chip at the center? Best I can make out is OZ9RR...

Toast

[obscurehero]

Re: Dell 1905FP Won't Turn On

Correct.

I'll need to bring my digital camera into work, but I'll try to get it posted for you this week.

This chip is tiny and there are a bunch of them:

029930G
517519127
0542

That's what I can make out.

What is it?

[retiredcaps]

Re: Dell 1905FP Won't Turn On

This chip is tiny and there are a bunch of them:

029930G

That is likely OZ9930G.

O2Micro makes quite a few of these PWM chips.

[obscurehero]

Re: Dell 1905FP Won't Turn On

Jets a good thing there are people out there who are excellent at electronics. I just googled PWM and got a technical page. Maybe if I spent enough time I could understand it, but the most I got is that it's a fancy dimmer. That right?

[retiredcaps]

Re: Dell 1905FP Won't Turn On

Maybe if I spent enough time I could understand it, but the most I got is that it's a fancy dimmer.

I like the videos by "Afrotechmods". Here he explains PWM

http://www.youtube.com/watch?v=YmPziPfaByw

edit: I'm still learning this stuff and sometimes my terminology isn't 100% correct. A year from now, I'll probably want to edit what I said to be 100% accurate.

[ryszardx]

Re: Dell 1905FP Won't Turn On

I have a 1905FP IPS board with 22uf cap. I replaced the caps The monitor worked for a while and now the ccfl just flash once and stay off. I noticed a smell coming from the monitor before it failed. It was faint almost like an ionization smell. anyway I inspected the board and didn't see anything except tha 2M ohm resistor next to the transformer looked brown around the circuit board edges. It tested within tolerance. I replaced the two 220uf caps next to the transformers with Panasonic caps. any ideas?

[PlainBill]

Re: Dell 1905FP Won't Turn On

I have a 1905FP IPS board with 22uf cap. I replaced the caps The monitor worked for a while and now the ccfl just flash once and stay off. I noticed a smell coming from the monitor before it failed. It was faint almost like an ionization smell. anyway I inspected the board and didn't see anything except tha 2M ohm resistor next to the transformer looked brown around the circuit board edges. It tested within tolerance. I replaced the two 220uf caps next to the transformers with Panasonic caps. any ideas?

Your description is a little ambiguous. Let's do this test.

Setup: All electrical parts of monitor together, case can be open or closed. Signal cable not hooked up

Hook up power. Press power button until power LED comes on. Do the backlights come on?

Do the backlights go off while the power LED stays on?

Does the power LED turn to amber (standby)?

Press the power button again. Does the power LED go off?

Press the power button once more. Does the power LED and the backlights come on?

If the answer is yes, check the wiring to the CCFLs,and inspect the CCFLs. Odds are there is a broken wire or broken CCFL.

If the backlights never come on, there is most likely an inverter problem. Suspect a shorted driver and a blown fuse.

PlainBill

[ryszardx]

Re: Dell 1905FP Won't Turn On

1. The backlight only flashes on when pushing the power button.
2. The power button remains green and no backlight
3. Power LED goes off when pressing again
4. Pressing once more same thing happens: backlight flashes split second and remains off
5. I connected known working CCFl's : same as #1 & #4
6. Fuse fine
I disconnected the blue side of one of the CCFL's : when powered on the backlight stays on approx. 2seconds instead of flashing.
Thanx again PlainBill

[PlainBill]

Re: Dell 1905FP Won't Turn On

1. The backlight only flashes on when pushing the power button.
2. The power button remains green and no backlight
3. Power LED goes off when pressing again
4. Pressing once more same thing happens: backlight flashes split second and remains off
5. I connected known working CCFl's : same as #1 & #4
6. Fuse fine
I disconnected the blue side of one of the CCFL's : when powered on the backlight stays on approx. 2seconds instead of flashing.
Thanx again PlainBill

That confirms it; two seconds to black. (True, apparently it was much shorter initially).

The 'ionization smell' is the real clue. It's time to examine the CCFLs and the wiring to them. The most likely cause is a bad solder joint at a ccfl. Another possibility is a broken CCFL.

PlainBill

[ryszardx]

Re: Dell 1905FP Won't Turn On

How does #5 fit in? I connected to known working CCFL's and the same symptoms are present.

[alexanna]

Re: Dell 1905FP Won't Turn On

How does #5 fit in? I connected to known working CCFL's and the same symptoms are present.

Have you tried adding fresh solder to the area of the inverter that was hot? Then retry the good CCFLs

[ryszardx]

Re: Dell 1905FP Won't Turn On

I, previously, resoldered those areas; figuring a bad solder joint would create heat from resistance. I will try it again.

[PlainBill]

Re: Dell 1905FP Won't Turn On

How does #5 fit in? I connected to known working CCFL's and the same symptoms are present.

Very good point, I missed that. Did you connect a full set of CCFLS?. If so, were they all the same brightness?

I'm now suspecting a bad (arcing) transformer.

PlainBill

[ryszardx]

Re: Dell 1905FP Won't Turn On

I am leaning towards your idea of suspecting a bad transformer. Is there a value for on board testing - i.e. resistance unpowered in primary and secondary?

[ryszardx]

Re: Dell 1905FP Won't Turn On

It could also be that I had one of the 22uf boards and the transformer was affected. I replaced the 22uf with a 2.2uf. But after that was when I was getting that smell from the unit. Maybe the transformer was already in a decline and with all new caps couldn't take the pressure?