Dell 2709w No power

[stj]

Re: Dell 2709w No power

can you trace back where the cap gets it's charge?
this is why i mentioned those 4 resistors - i'v seen resistors in series feeding startup circuits before.

[budm]

Re: Dell 2709w No power

"Between 1>5 & 3>4 I see 0.5Ω"
What resistance do you get again between pin 1 and 3 of the transformer as marked in your picture?

[Per Hansson]

Re: Dell 2709w No power

budm: The value seen on the transformer between leg 1>3 is now: 280Ω & 4>5 is now 290Ω
They where at 320Ω before?
Have not checked the K3679 MOSFET on HS1 marked Q601 yet.

jetadm123: No I did not check VCC on P1203D60 before I put back the transformer, will check your other points later.

[Per Hansson]

Re: Dell 2709w No power

Did you check the Source to Drain of that MOSFET on the HS1 to see if it show low resistance?

K3679 MOSFET on HS1 marked Q601:

Source > Drain = 285Ω
Source > Gate = 7.8Ω

[jetadm123]

Re: Dell 2709w No power

Appears to be a short at S-->G. Suggest you remove Q601 from board and check it again.

[budm]

Re: Dell 2709w No power

Yep, remove and test it off the board.

[Per Hansson]

Re: Dell 2709w No power

The test was done with Q601 removed from the board.
So you say it's dead then?
Datasheet for Q601 (K3679 MOSFET) attached

[budm]

Re: Dell 2709w No power

So what resistance do you get now on the MOSFET of the board between S and D, S and G, D and G?

[Per Hansson]

Re: Dell 2709w No power

I never tested it in circuit, so values are as posted before more or less:

Source > Drain = 275Ω
Drain > Gate = 275Ω
Source > Gate = 7.8Ω

[budm]

Re: Dell 2709w No power

That Drain to Gate low resistance could have caused damage to the GATE DRIVE output of the SMPS IC.

[jetadm123]

Re: Dell 2709w No power

Agree with budm. You should also consider replacing the 1203p60 along with Q601.

[budm]

Re: Dell 2709w No power

BTW, do you also see any liquid coming out of the legs of that main filter cap (big brown cap with 450VDC rating), that is one of the common failure cap.

[Per Hansson]

Re: Dell 2709w No power

No the main filter cap measured fine in circuit: 160uF & 0.5ESR
It's a UCC KXG 450v 150uF capacitor.
And it looks fine too

[Per Hansson]

Re: Dell 2709w No power

It's working now!
Replaced Q601 & IC601

Thanks allot for the advice guys!

[budm]

Re: Dell 2709w No power

Thanks for the follow-up.

[rocket]

Re: Dell 2709w No power

Update: I finally had time to crack open the screen. Applying pressure to the main BGA (FLI30366) while plugging it into the mains allowed the monitor to start up. As soon as some flux arrives I'll be attempting to reflow the chip.

[petasis]

Re: Dell 2709w No power

Hi all,

I also have an 2709W monitor, which also stopped (gradually) working.
It started with loosing signal from PC a few times a day, the disconnects increased in frequency, until yesterday I couldn't get it to show any input.
After a few cycles of turning it on/off, it got into the state where when powered up only the blue led was on (no dell logo on screen), and in the next power on, even this blue led does not show up.

I opened the monitor, no bad cups inside... :-)

[selldoor]

Re: Dell 2709w No power

Can you spot the difference between the first post in this thread and yours?

[petasis]

Re: Dell 2709w No power

I measured similar voltages:

The big cap: 315 V
1 (to most black wire) - 0v
(empty)
2- 0v
3- 23.5V
4- 0v
5- 23.5V
6- 23.5V
7- 0V
8 (bottom grey wire) - 0V

The voltage in mine is 23.5V, not 24V. But in general, the voltages are as described on the first post. The blue led does not lit.

(It used to be, but now it doesn't)

[selldoor]

Re: Dell 2709w No power

ok - so straight on clear pictures of your boards and the voltages on the
main board?