Dell E178FPc-Only Power LED

[MEB]

Hello,

Don't know much, but want to learn.

I have a Dell E178FPc Rev A00.

The only thing that visually works is the green Power LED. It cycles on/off correctly as button is cycled manually. I have the monitor connected to a known good PC. Screen never changes from black and I even tried the flashlight thing I read about here and see nothing.

I have attached photos of the boards and one of connector CN902 on the Power board. All the capacitors look fine and I checked all of them with my "blue" meter and the values look ok to me. I will repeat and report all values if advised and am willing to replace all the caps, but I don't want to unless necessary.

I have measured DC voltages at CN902 and will list them. Pin 1 is O/F and Pin 3 is DIM and I do not know what O/F and DIM mean, so would appreciate knowing.

Pin 1 - O/F - 2.795V DC
Pin 2 - Blank
Pin 3 - DIM - 4.360V DC
Pin 4 - 12V - 14.60V DC
Pin 5 - GND
Pin 6 - 5V - 4.892V DC
Pin 7 - 5V - 4.892V DC
Pin 8 - GND
Pin 9 - GND

I realize this is not a lot to start with, but un-instructed poking around seems to get me in trouble.

I am looking forward to fixing this, but I need help. Thanks.

[selldoor]

Re: Dell E178FPc-Only Power LED

Hmm-- On the back of the power board there are two items labelled F902 and F903 they are actually zero rated
resistors but can you test them as you would a fuse. Power off Meter on ohms 200
one lead on each end of fuse. May also be a an F901 but havent found it yet.

One is at top left corner then scroll across halfway is the other

[MEB]

Re: Dell E178FPc-Only Power LED

Thanks for the reply.

Found F902 and F903 and both read .2 ohms. Also found F901 which doesn't look like the other 2, but must be a fuse printed with 2A 250V and it also read .2 ohms.

[selldoor]

Re: Dell E178FPc-Only Power LED

Darn!! they are all ok. and you get no flash at all from the backlights? - try in a dim room.

[MEB]

Re: Dell E178FPc-Only Power LED

Ok. I put everything back together on the table and shut off the lights. When I plugged the monitor into AC, the screen lit a dim gray for about 2 seconds, then went black. I pressed the power button and the green LED came on, but the screen stayed black. Cycling the power button a few times cycles the LED, but the screen stays black.

Unplugging and re-plugging the monitor into AC, again lites the screen gray for a couple seconds and the power button again cycles the LED only. This is repeatable.

[selldoor]

Re: Dell E178FPc-Only Power LED

The voltages look a little low might need 3v on the o.f to start it so may need to test the voltage regulators on the main board I think I see 2 .

Do you have a 3 volt battery cr2032 or 2 * 1.5v AA or a 1kw or .5kw resistor

[MEB]

Re: Dell E178FPc-Only Power LED

I have a 3V CR2016 plus spares for my watch and 2 AA's in my flashlight. The resistors, maybe, but I would have to do some exploring.

[selldoor]

Re: Dell E178FPc-Only Power LED

Ok whichever you are most comfortable with- unless you can rig a holder for the AA the cr2016 is easier to hold on to.
Switch off - if its on- then disconnect the cable to the main board.
Switch it on then use the battery to supply 3v to the o/f pin.
One wire from battneg to either the ground pin or to a nearby ground screw and battpos
to the o/f pin. Doesnt alway work but worth a try. Obviuosly you wont get picture but the back lights might stay on. Try and keep them on for half a minute or so.

[MEB]

Re: Dell E178FPc-Only Power LED

I soldered a wire to each side of the 3V battery after testing it on a little battery tester. I left the monitor connected to the PC and AC and shut the power button off. Green LED went out. I removed the cable coming from CN902 at the main board and pressed the power button back on. Green LED did not light. I attached the negative wire from the battery to the ground wire from the power board and the positive to the corresponding O/F pin on the main board connector. Nothing happened. I cycled the power button a couple times and still nothing.

Either I goofed or it didn't work?

[budm]

Re: Dell E178FPc-Only Power LED

I will have to look over the pictures of your board, more likely the problem will be in the inverter section.
Base your post:
Pin 1 - O/F - 2.795V DC
Pin 2 - Blank
Pin 3 - DIM - 4.360V DC
Pin 4 - 12V - 14.60V DC
Pin 5 - GND
Pin 6 - 5V - 4.892V DC
Pin 7 - 5V - 4.892V DC
Pin 8 - GND
Pin 9 - GND
All the signals are correct.
What are the P/N of Q805, 806?

[MEB]

Re: Dell E178FPc-Only Power LED

Welcome and thanks budm.

Q805 and Q806 are APM9945.

[budm]

Re: Dell E178FPc-Only Power LED

OK, check the resistance reading on betweem S1 (pin 1) and D1 (pin 8), S2 (pin 3) and D2 (pin 5).
See the spec sheet.

[MEB]

Re: Dell E178FPc-Only Power LED

Not sure what I'm doing here. With my meter set on ohms, putting my black lead on S1 (1) and my Red lead on D1 (8) I initially read 500+ kohms, but the longer I stay on it the lower the reading goes. Similar reading on S2 to D2. Somewhat the same thing on both Q805 and Q806.

[budm]

Re: Dell E178FPc-Only Power LED

OK, you are just see the caps being charge, what we are looking for is resistance of less than 200 Ohms. So the MOSFETs are OK. I need to look further on your board. There is the PWM IC (IC801, close to the MOSFETs) that drive the MOSFETs, can you read the numbers?

[MEB]

Re: Dell E178FPc-Only Power LED

There is IC801 which is a 16 legged device nearby with 0Z9938GN and a bunch of other numbers on it. Does that sound right?

[MEB]

Re: Dell E178FPc-Only Power LED

I found this datasheet if it helps.

[budm]

Re: Dell E178FPc-Only Power LED

OK, I will look at the spec. mean while you can take DC voltage reading on the PINS (except ground pin).

[MEB]

Re: Dell E178FPc-Only Power LED

OK, This is what I found. A couple * means I don't think it was any real DC value.

Pin 1 - -.017V DC
Pin 2 - 4.719V DC
Pin 3 - **
Pin 4 - 3.923V DC
Pin 5 - -.017V DC
Pin 6 - **
Pin 7 - **
Pin 8 - Blank
Pin 9 - Blank
Pin 10 - 4.677V DC
Pin 11 - **
Pin 12 - **
Pin 13 - 4.705V DC
Pin 14 - **
Pin 15 - **
Pin 16 - Did not test per your instructions

[budm]

Re: Dell E178FPc-Only Power LED

I did not have a chance to look at the details spec yet, funny thing is that, the spec has E-MAIL in it also. Where did you download the spec sheet?

[MEB]

Re: Dell E178FPc-Only Power LED

I got it from www.datasheet4U.net. I couldn't read all that Chinese stuff either.

Thanks for hanging out with me budm. It is an honor to have you help me. It is past this old man's bedtime and I still have to drive home so hoping to continue on again soon.