Dell 1707FP no power

[3d0]

Re: Dell 1707FP no power

Hi guys, I have the same problem.
Can someone please confirm that the power supply is ok, before I orded a logic board.
I have tested it and found that all voltages are the same as terry and bob12345 have.
Thanks

[selldoor]

Re: Dell 1707FP no power

Presumably you expect us to trawl back through the thread ??
Well I'm not going to.

[3d0]

Re: Dell 1707FP no power

Presumably you expect us to trawl back through the thread ??
Well I'm not going to.

Here's what someone suggested:

Measure the voltage on the three pins of U404. Also, there are three voltage regulators to investigate. Measure the voltage on all three pins of U601, U602, and U902.

PlainBill

Done all of that, and the measurements are:

U404:
Pin 1: 0V
Pin 2: 0V
Pin 3: 1.24V

U601:
Pin 1: 0V
Pin 2: 5.21V
Pin 3: 1.24V

U902:
Pin 1: 0V
Pin 2: 0V
Pin 3: 0V
Pin 4: 0V

U602:
Pin 1: 0V
Pin 2: 0.4V
Pin 3: 1.24V
Pin 4: 0.4V

Here's a image of the logic board. I think the power supply is somewhat ok, since the LB has voltage on certain points. Just need someone more smarter then me to confirm that.

Thanks

[Davi.p]

Re: Dell 1707FP no power

Hi 3DO (old console lover eh!) unfortunately the OP did not continued to update this thread, after all the effort Plain Bill had put, i think you have to do the tests P.B. suggested to know if it is worth to replace the regulator/s, then post back the results. P.B. don't noticed and added that there is an onboard usb hub then maybe its normal that U902 (if i remember) doesn't take and give power, another test you can do is to put an external 3,3v like the one from an ATX psu to the U601 output and see if mon. works.

[budm]

Re: Dell 1707FP no power

OK, lets get the pinout of the voltage regulator (1117 series) correct first, see the info here:
https://www.badcaps.net/forum/showth...579#post406579
Then report the reading according to the pins.
Looking at it with big tab up (big tab is tied internally to the center pin), left pin is 1 (adj/Gnd), Middle is 2 (output), right is 3 (input).
Voltage between pin1 and pin2 will always be 1.25V.

[3d0]

Re: Dell 1707FP no power

Thanks guys for your time and interest in this crapy old monitor.
Davi.p it does have a external usb hub.
Maybe after these readings we should try to put 3.3V on the output pin like you said, do I have to take the ground form the ATX PS and solder it on to the gnd on the logic board. Stupid question but just want to double check before I fry something.

So I measured the 1117R-33 voltage reg.

pin1-Left pin= 0V
pin2-Middle pin= 1.24V and every second or so it jumps to 1.25V (it should be 3.3V correct?)
pin3-Right pin= 5.24V

Thanks again.

[Davi.p]

Re: Dell 1707FP no power

"Thanks guys for your time and interest in this crapy old monitor."
I don't like these words, don't seem a crappy one to me..

"Maybe after these readings we should try to put 3.3V on the output pin like you said, do I have to take the ground form the ATX PS and solder it ..." Yes you must..

For the rest i told you that thus regulator must be pulled out like PlainBill suggested.. read the rest..

[3d0]

Re: Dell 1707FP no power

It's not going to be crappy if we fix it, right!
I read the thread a couple of times, English is not my native language, plus I'm a noob at electronics so it's quite hard. After your & budm post I'm starting to understand more about these logic boards and how they function.
So, I'm going to pull out an old atx ps, and try what you said, I'll report back the findings.

[Davi.p]

Re: Dell 1707FP no power

wait wait wait... don't do that first, first you have to desolder the U601 and test it outside circuit, i refer to what said P.Bill that is an expert, give it a Vin of 5v and a load resistor of 25ohm, test the central pin, if it is good 3,3v the fault is still on the board, so test the connected alluminium caps for short..

[3d0]

Re: Dell 1707FP no power

Oh crap, I have already done it while the U601 was in the circuit!
But you where right, the lcd did turn up, so that's good to know.
The next step is to desolder U601 and test it, but before that I need to figure out how to give it a Vin of 5V with a load resistor of 25ohms? Total noob pls forgive me, I guess I'll find a explanation somewhere on the forum.
Do you mean the alluminium caps that are on the main psu, these circled in red on the picture?

Thanks again.

[selldoor]

Re: Dell 1707FP no power

No - He means the Aluminium capacitors on the Main Board (the green one)
The capacitors that are connected directly to the Voltage Regulators like C604 and C607
English is not Davi,p' s first language either so its going to be difficult

[3d0]

Re: Dell 1707FP no power

Thanks for the explanation selldoor.
I took the 1117R-33 voltage reg out of the circuit, put 5.25V on the Vin pin, and the Vout has a reading of 4.4V?

[Davi.p]

Re: Dell 1707FP no power

For the 5v you can use the psu board of the monitor detached from the rest, for the resistor i can't help you but 25ohm is an uncommon value, i think you can grab a 27ohm, red purple black gold stripes, solder on the regulator some test wires that you connect to psu and resistor..

[budm]

Re: Dell 1707FP no power

"I took the 1117R-33 voltage reg out of the circuit, put 5.25V on the Vin pin, and the Vout has a reading of 4.4V?" That sounds like the Ground pin (pin1) is not connected to the ground.Bad input and output cap for the regulator can be bad and causes the output to Oscillate, so you do need to check those caps also.

[3d0]

Re: Dell 1707FP no power

Pulled both of the caps out, since I don't have a ESR meter, nor can I measure capacitance with my DMM I will replace them with new ones, also ordered a new voltage reg. Took a little risk, but hey.
Just need to wait for 10 days for the parts to arrive, hopefully that would be all that needs to be replaced, we will see I guess.

Thanks again guys, you're help is appreciated.

[3d0]

Re: Dell 1707FP no power *SOLVED*

Ok, so the Voltage regulator arrived (1117R-33) , replaced the old one and the monitor works now!

Bought it on ebay:
Sipex (Alpha) 3.3V/800mA Positive Voltage Low Drop-Out Regulator, Part Number: AS1117R-3.3TR

Big thanks to davi.p, budm & selldoor for the help.

Quick note: this is a Dell 1707Fpf model lcd, the original poster made a mistake in the title.