Dell LCD E198WFPF no power

[albertwong]

I recently got a Dell LCD E198WFPF with no power, not even the green power light on the monitor.
I opened up and checked the power/inverter board. There is no obvious problem with the capacitors. The fuse is good.
I measured the output and there are 5V and 3.3V output. however, no 12V power can be found. Is that normal?

The dispaly board is
ILIF-027 490941300000R
Could it be the problem of reset control circuit?
I remember I saw in here there was a post about ACER monitor with reset circuit bad. But I do not have the schematic. I dont know how to locate the reset circuit.
Anyone have any idea?

[PlainBill]

Re: Dell LCD E198WFPF no power

I recently got a Dell LCD E198WFPF with no power, not even the green power light on the monitor.
I opened up and checked the power/inverter board. There is no obvious problem with the capacitors. The fuse is good.
I measured the output and there are 5V and 3.3V output. however, no 12V power can be found. Is that normal?

The dispaly board is
ILIF-027 490941300000R
Could it be the problem of reset control circuit?
I remember I saw in here there was a post about ACER monitor with reset circuit bad. But I do not have the schematic. I dont know how to locate the reset circuit.
Anyone have any idea?

Yeah. Attach a picture. The internet is wonderful, but it doesn't give us an image of what you are working on unless you take one.

PlainBill

[EGuevarae]

Re: Dell LCD E198WFPF no power

Yeah. Attach a picture. The internet is wonderful, but it doesn't give us an image of what you are working on unless you take one.

PlainBill

12v output to Video/main board? Yes. It is not common to have such voltages on the main board (I said rare, not impossible....).
12v is used just for the inverter (12v,13v,15v,18v, 20v, depending on the "inverter" section of the board).
I agree with Bill. Post pictures to start looking for an answer.

[albertwong]

Re: Dell LCD E198WFPF no power

Thank you so much for your replies.
I am sorry for the last reply.
My work got really busy last few months.

I took the picture of the display board and power board.





Your help is much appreciated.
I think the inverter is working.
I measured the main filtering cap is with line voltage.

[PlainBill]

Re: Dell LCD E198WFPF no power

Thank you so much for your replies.
I am sorry for the last reply.
My work got really busy last few months.

I took the picture of the display board and power board.

Your help is much appreciated.
I think the inverter is working.
I measured the main filtering cap is with line voltage.

PLEASE don't insert pictures in your posts. Do it this way.

I've marked up the power supply board and the logic card.

Power supply / inverter. I've circled the 8 pin connector for the cable to the logic card. Measure the voltage from each of the pins to the point I've marked Gnd.

Logic card. I've circled two voltage regulators. Measure the voltage from the 3 pins to the point I've labeled Gnd.

PlainBill

[albertwong]

Re: Dell LCD E198WFPF no power

PlainBill, I wanted to modify the picture as attachments. But how can I edit the post?
There is no edit icon.

I am going to measure the voltages tonight.

[PlainBill]

Re: Dell LCD E198WFPF no power

PlainBill, I wanted to modify the picture as attachments. But how can I edit the post?
There is no edit icon.

I am going to measure the voltages tonight.

You can't. That means the over-sized pictures will stay in the thread forever, sucking up bandwidth every time someone steps through this thread.

And they are such good, clear pictures, too.

PlainBill

[albertwong]

Re: Dell LCD E198WFPF no power

I have an idea. I can modify the picture and put some reduced size picture with the same name and upload the real picture in another reply.

[albertwong]

Re: Dell LCD E198WFPF no power

Here's the original picture for my power board and logic board.

[albertwong]

Re: Dell LCD E198WFPF no power

I just measured the voltages.

The power board.
The voltage from the pins to ground is as following:
1 2 3 4 5 6 7 8
0.02 3.25 0.02 0.01 0 0 4.9 4.9


The logic board:
The 2 voltage regulator has voltage as following:
Location according to the picture
-------------------------------4.54------3.25----0.01
------------------------------- l----------l---------l
----------------------------------------------------
-------------------------------------------l
-----------------------------------------3.25




-------l - 3.25
1.78 - l - 1.78
-------l - 0.01

Is it normal?

[PlainBill]

Re: Dell LCD E198WFPF no power

I just measured the voltages.

The power board.
The voltage from the pins to ground is as following:
1 2 3 4 5 6 7 8
0.02 3.25 0.02 0.01 0 0 4.9 4.9


The logic board:
The 2 voltage regulator has voltage as following:
Location according to the picture
-------------------------------4.54------3.25----0.01
------------------------------- l----------l---------l
----------------------------------------------------
-------------------------------------------l
-----------------------------------------3.25




-------l - 3.25
1.78 - l - 1.78
-------l - 0.01

Is it normal?

Those voltages don't look terribly wrong. There is often a voltage drop from the power supply to the logic card. A 0.4V drop is reasonable. The interface of the control chip probably requires 3.3v; 3.25 is also reasonable. And the processor itself often uses 1.8 volts; 1.78 is right on.

The last time I saw something like this, it was a bad reset controller for the processor. Also, a bad crystal could do it.

More research is needed; I'll reply tomorrow.

PlainBill

[albertwong]

Re: Dell LCD E198WFPF no power

Oh, I think I read your other post about the reset controller.
Is it for an Acer monitor?
You really is great. You helped a lot of people.
Thank you so much for your time and effort.
You help is much appreciated.

[PlainBill]

Re: Dell LCD E198WFPF no power

Sorry, but at this time I'm coming up blank on this problem. The problem is apparently on the logic card. Unless you have access to an oscilloscope, replacing the crystal is the only reasonable approach. If that doesn't work, replacing the entire card is the only other option.

PlainBill

[albertwong]

Re: Dell LCD E198WFPF no power

If I have an oscilloscope, what can I check?
I have an old oscilloscope, but it is not working that well.
But I can give it a try.

[MDOC]

Re: Dell LCD E198WFPF no power

Rather strange that you have good regulator output voltages but the power indicator is not lit. If the indicator comes off the logic board then the problem is on that board. That'd be my guess.

[PlainBill]

Re: Dell LCD E198WFPF no power

Rather strange that you have good regulator output voltages but the power indicator is not lit. If the indicator comes off the logic board then the problem is on that board. That'd be my guess.

You're missing one fact. The power LED is controlled by the processor. No processor action, no power LED.

PlainBill

[PlainBill]

Re: Dell LCD E198WFPF no power

If I have an oscilloscope, what can I check?
I have an old oscilloscope, but it is not working that well.
But I can give it a try.

Check the pins on the processor that connect to the crystal. You're looking for signs of oscillator action.

PlainBill

[albertwong]

Re: Dell LCD E198WFPF no power

I will check it with my scope there then.
I hope it is the crystal, then it would be easier to fix.
How do you found out the frequency of the crystal?
I am just curious, why wouldn't you think that it is again the reset controller this time?

[PlainBill]

Re: Dell LCD E198WFPF no power

I will check it with my scope there then.
I hope it is the crystal, then it would be easier to fix.
How do you found out the frequency of the crystal?
I am just curious, why wouldn't you think that it is again the reset controller this time?

The crystal is the metal 'can' just above the processor in the picture of the logic board. It's frequency is stamped on the top.

I suspected a bad reset controller, but I don't see anything that looks like it could be one. The one I am familiar with was a three pin package, much like the 'chips' to the left of the processor in the picture. However, those have a location designation that starts with D; they are diodes. The reset controller location designation would start with U. It is also possible that the reset controller is incorporated in the processor itself. Without a datasheet I can't be sure.

PlainBill

[albertwong]

Re: Dell LCD E198WFPF no power

The crystal is the metal 'can' just above the processor in the picture of the logic board. It's frequency is stamped on the top.

I suspected a bad reset controller, but I don't see anything that looks like it could be one. The one I am familiar with was a three pin package, much like the 'chips' to the left of the processor in the picture. However, those have a location designation that starts with D; they are diodes. The reset controller location designation would start with U. It is also possible that the reset controller is incorporated in the processor itself. Without a datasheet I can't be sure.

PlainBill

I see. Thanks for the explaination. I found my oscilliscope yesterday. However, I cannot find the probe. I think I placed those in some other location. I will try to find those probes today and see what the processor got.