Dell 2709w No power

[ytsoc]

Re: Dell 2709w No power

Back with good news.
Thanks to Neil who sent me his board so i can copy that eeprom, i got my monitor up and running again.

Bonus i managed to fix his board too by reflowing the same bga chip.

[Per Hansson]

Re: Dell 2709w No power

A question to you that have this monitor, heatsink (HS1) to the right of the bulk filter capacitor in the picture below does it become really hot?

Mine emits a crazy amount of heat, so far I've only looked at this monitor briefly.
The cap has 378VDC across it's legs with 230VAC on the incoming
There is no voltage at all on the 24v output connector.

[budm]

Re: Dell 2709w No power

As you notice, they put the thermal transfer pads (4) to transfer the heat to the chassis, they do run hot. Did you check the temperature to see how hot it is?

[Per Hansson]

Re: Dell 2709w No power

It was too hot to touch, I will get a temperature probe & check how quickly it's heating up.
Does anyone have a schematic for this PSU?
I will compare all voltages with the first post in this thread, a little later when my brain starts working (It's 30°C outside now )

[jetadm123]

Re: Dell 2709w No power

Did you check fuse F701 next to the wiring harness? I believe that's the fuse for the 24V output.

[Per Hansson]

Re: Dell 2709w No power

No I did not, just did a real quick check before going to a lake for a swim
Will check later tonight, thanks for pointing it out!

[Per Hansson]

Re: Dell 2709w No power

Ok, had some time to look into this monitors PSU now.
It takes ca 2min for HS1 to go from 35°C to 75°C (logic board & backlight disconnected)

The fuse F701 checked out fine.

C606=10.4v
C611=10.8v
C622=33v (slowly builds from ca 32.5v > 34v under 1 min)

VCC on IC651=10.7V (ST: L6561 PFC Controller)
VCC on IC601=10.8V (On Semiconductor: 1203P60 PWM Controller)

I have labeled the pins on transformer T601 in the attached picture.
Between 1>5 & 3>4 I see 0.5Ω
Between 1>3 & 4>5 I see 320Ω
Between 1>3 & 4>5 I also see 375V

On the other side of the transformer there is 0v between all legs & resistance is 0.4Ω
So the problem is probably in the transformer (1J.20319.001) or the rectifiers D701 or D703 (VF20200C) that follow.
It's time for bed now though, so will have to desolder them tomorrow to look further.

[selldoor]

Re: Dell 2709w No power

Any voltage on the caps C711to C715 - the ones in a row along the edge

[Per Hansson]

Re: Dell 2709w No power

No the entire output is dead...
Took another picture of the board and played a bit in Photoshop:

[stj]

Re: Dell 2709w No power

what's the part number on ic651?
and can you check the value of the 4 blue resistors to it's left.

[Per Hansson]

Re: Dell 2709w No power

IC651 is a ST L6561 PFC Controller, I attached it's datasheet in a post above now.
The four resistors R657, R658, R660 & R661 all measure within 1% of 1MΩ out of circuit.
Their color codes are Brown, Black, Black, Yellow, Brown which = 1MΩ

I desoldered the 2x VF20200C rectifiers D701 & D703
Resistance was still 0.4Ω between the output legs of the transformer.
So I desoldered the secondary side of the transformer, resistance on it was the same.
Resistance on the now empty traces on the PCB changed from 0.4Ω to infinite resistance.
When I applied power there was no change:
The HS1 heatsink still heated up the same way and there was no power on the output of the transformers legs. (which now where in the air).
I take it the transformer is bad?

[selldoor]

Re: Dell 2709w No power

I dont think these type of transformers show a resistance on the secondary windings
until they are working at which point you cant measure them im sure budm has mentioned this a few times I will try and find it. (in case i just made it up )

[selldoor]

Re: Dell 2709w No power

It was here I last read it
https://www.badcaps.net/forum/showpo...36&postcount=3

[Per Hansson]

Re: Dell 2709w No power

Hmm ok but even if the low ohm reading is ok (keep in mind 0.4Ω with my fluke is pretty much a dead short)

How can there not be voltage present on the secondary, I mean there is high voltage on the primary, surely there must then be voltage on the secondary winding?

[selldoor]

Re: Dell 2709w No power

What voltage is there on the Vcc pin on the 1203P60

May be around 5-12v but careful high voltage area

[Per Hansson]

Re: Dell 2709w No power

Selldoor:

VCC on IC601=10.8V (On Semiconductor: 1203P60 PWM Controller)

[selldoor]

Re: Dell 2709w No power

OK think that is too low- so next test the voltage on the start up cap perhaps 47uf 50v

C606?? haha - just seen it 10.4v

Also too low - suggest change this cap



NOTE to SELF - Read the thread properly !!!

[jetadm123]

Re: Dell 2709w No power

There appears to be several revisions of this same power supply used in the large screen Dells. All made by the same company and all pretty lousy! If you do a search on this website for a Dell 2408WFp, there should be a schematic. The design is slightly different, but it's baseline enough to help aid in your troubleshooting.

1) the 1203p60 needs at least 12.8v to turn on correctly. It could still be the 47uf startup cap. Do you have a spare to substitute? Also, check the zener diode across that 47uf cap.

2) Check Q601 for shorts.

3) If you suspect the transformer, did you check the Vcc of the P1203d60 after you unsoldered the secondary? It should rise if there was a short.

[budm]

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?
BTW the T601, pin 3 and 4 is the primary winding, pin 1 and 5 is the AUX winding.

[Per Hansson]

Re: Dell 2709w No power

Replaced the two caps, their capacitance tested good, ESR read 0.7
Only 0.1v difference with the new caps installed with regards to measured voltages previously:

C606=10.4v
C611=10.9v
VCC on IC601=10.9V