Dell 2709w No power

[newbie1]

Hey guys,

First of all, thank you for those who are still keeping this forum alive.
It has been a while since I posted.
Probably because most of the monitors are all plain sailing repairs, or I am shamelessly buying or swapping cheap power/logic boards. Hee.
Right now, I am facing with two big monsters, or should I say ‘white elephants’, which are ‘Dead’. One of them could be intermittently revived if NOT unplugged from the mains. (But recently could not ON at all even leaving it plugged for hours) The other could not be turned on at all. I could not find any schematic on the internet on this model. I hope someone can assist me in troubleshooting them.

Model : Dell 2709w
(Photos as attached and both boards are the same model 4H.0GY02.A00)

Set#1 –
What I managed to measure on the power board–
*Big Cap – 325V
*Voltage out to the main board
1 (to most black wire) - 0v (3.1V if turn ON)
(empty)
2- 0v
3- 24V
4- 0v
5- 24V
6- 24V
7- 0V
8 (bottom grey wire) - 0V (3.1V if turn ON)

*Across electrolyte cap 47uf (C11) (next to IC601) – 14V
*Across electrolyte cap 1uf (C622) (next to IC651) – 33V
* VCC of IC601 (123p60) – 14V
* VCC of IC651 (L6561) – 0V!!

What was done – Replaced the entire electrolytes. Re-measured the above and they are still the same. No power. Unfortunately while measuring the VCC of IC601 I shorted it out; there was a spark, loud BANG! and resulting in killing many components (2 SMD resistors blown, Diode K3679 on heatsink, D604 & ZD601 – shorted and main fuse goes south). Oh well!

Moving on to Set#2

What I managed to measure on the power board–
*Big Cap – 325V
*Voltage out to the main board
1 (to most black wire) - 0v (3.1V if turn ON)
(empty)
2- 0v
3- 24V
4- 0v
5- 24V
6- 24V
7- 0V
8 (bottom grey wire) - 0V (3.1V if turn ON)

*Across electrolyte cap 47uf (C11) (next to IC601) – 14V
*Across electrolyte cap 1uf (C622) (next to IC651) – 33V
* VCC of IC601 (123p60) – 14V
* VCC of IC651 (L6561) – 0V!!
What was done – No replacement of electrolytes because from Set#1, they do not rectify the failure.
Continue to trace the VCC of IC651 (L6561) ( 0V) and it leads me to the Gate pin of SMD Q554 (directly below ZD601). The Base and Emitter of this diode is Both reading 14V though.

So my questions are
1) Am I concluding it rightly by focusing on the power board or the mainboard could also be causing them to be dead?
2) Am I right to say that VCC of IC651 (L6561) should be the range of 14V also? If yes, could it be the IC622 (L6561) is faulty (not producing 14V) or should the Gate of SMD Q554 be supplying it instead to it?
3) Any other measurement should I be taking?

Apology for the blurred pictures, please let me know if any one needs a better lighted image. or i can link to my dropbox folder?. Damn! I should have placed it on the floor while taking the pictures. Lol!

Thank you in advance for all your replies

[Neill]

Re: Dell 2709w No power

Hi there.

I have one of these in pieces and have studied it in great detail.

The power supply makes just one Voltage which is 24V.

If you have this Voltage present at the connector CN701 then I think the problem will be with the logic board.

I know it's been a while since your post so are you still interesting in getting this monitor going?

https://www.badcaps.net/forum/images/smilies/rockon.gif

[Neill]

Dell 2709W DC O.K. but no go.

Since I cannot start a thread yet I figured I would tell my story here:

So I have this Dell 2709W. The power supply is on a separate board and produces 24VDC. When plugged it in at the wall the power supply makes 24VDC O.K. On the logic board the 24V s converted into 5V and 3.2V(plus and additional +5V and +12.4V when on). The 3.2V is further converted to 1.8V. All these supplies are O.K.

If I connect up an external 24VDC power in place of the power supply board the behavior is the same, the supplies are there but the monitor will not turn on, not even the standby LED comes on.

The standby LED, Power LED and control buttons are all proximity type and are on a board that communicates with the main logic board via I2C, using a SO380001.

Now here is where it get's interesting...
My bench power supply has a current limit feature. With the current set to 0 and if I snap it to full the current draw will be around 60mA and the monitor will not power on.

But with the current set to zero and if I wind the current up slowly then the current draw will settle to just 10mA. Then when I put my finger near the power button the monitor powers up(I have the back light module disconnected!). I can then activate the menu buttons by placing my finger near them(they light up and a beeper sounds). I can then power off by again putting my finger near the power button.

This process can be repeated reliably all day long. Snap the power on and the monitor refuses to do anything. Wind the current up slowly and it will work.

Of course when I connect the main board to the monitors CPU the current comes up very quickly so it just sits there not doing anything. In this state you can actually get it to come on by switching off the mains then quickly turning it back on again, takes a bit of practice!

So there you have it. Anyone got an idea what might be going on?

Sorry to hi-jack this thread as such but I think what I'm seeing is likely to be the same issue as the OP has/had.

I really should just give up on this one but I've kind of become obsessed with it.

[Neill]

Re: Dell 2709w No power

Still battling this monitor. I have started drawing up my own schematics. I'm beginning to think this monitor is not repairable. Anyway here are some photos:

This is the layout with the back off. The power supply module makes just one Voltage, +24V. When the power is on the mainboard sends a signal to the power supply however no extra outputs are enabled and the output Voltage does not change. I suspect the signal is there to get the power supply into a high power mode.



Here is a close up of the various secondary supplies which are made on the main board. I have replaced all the electrolytic capacitors here. All the supplies are fine, with no ripple. I have labelled the power supply connections. Another way to get the monitor to work is to keep the +24V connections on the blue and green wires, then apply the 24V to the orange wire.



Here is a close up of the keyboard connector J13. When power is applied to the monitor the +5V is present however there is no activity on the SCL and SDA lines. If I trick the monitor into starting up by slowly ramping up the power then the CPU initializes and there is activity on the SDA and SCL lines, then you can power the monitor on. Regardless of whether the CPU initializes or not the 19.6608MHz crystal runs.



Such a mystery....

[stj]

Re: Dell 2709w No power

startup / reset circuit is what to look for.
can the get the microcontroller datasheet/pinout?

it maybe be the old cap-resistor type.

[Neill]

Re: Dell 2709w No power

startup / reset circuit is what to look for.
can the get the microcontroller datasheet/pinout?

it maybe be the old cap-resistor type.

Thanks for that, I feel you might be right about where to start looking.

Unfortunately it is a BGA package and a multilayer board. There does not appear to be a separate reset chip, so I see if I can find a reset pull-up resistor that could the the rest line.

[Neill]

Re: Dell 2709w No power

The micro is the all-in-one FLI30366, with 416 pins in a PBGA format. I can only find a summary datasheet, not a pinout. Seems to be an obsolete chip, first made by Genesis who were acquired by ST.



Still hunting.

[stj]

Re: Dell 2709w No power

then look for suspect small caps - 4.7-47uf at some low voltage.
they will have one pin connected to the power, the other pin connected to a resistor that goes to the other power rail.
the joint between the 2 goes to the reset input on the chip.

what does the underside of the board look like?
sometimes with bga you get all the via's on the othe side of the pcb.

[Davi.p]

Re: Dell 2709w No power

"to the other power rail." You mean the ground? From a casual service manual (Acer al1717) i see the reset pin (RST) connected to GND through a 10k resis. and to +5vcc through a 10uF25v cap. I have thought why a worn cap can prevent the reset line to activate with a normal psu and not with a gradual current? It is not that there is a power up stage when psu outputs a low current as you said and the circuit behind or after the second opto doesn't work well? Is there an LM393 on the video board? Anyway i could not understand even with a schematic

[stj]

Re: Dell 2709w No power

one is ground, the other is vcc.
i cant say what way around because it depends on the polarity of the reset signal.

[stj]

Re: Dell 2709w No power

maybe the cpu has to reset within a specific time after power is applied - such as if there is another mcu in the system.

[Neill]

Re: Dell 2709w No power

Firstly thanks for the replies and suggestions guys. I work with micro controllers all the time so I'm familiar with reset circuits. Can't say I've ever came across a faulty one before, well accept when I've messed up the design of one!

But it would seem that this monitor is indeed having a problem with reset.

I have traced what could be a reset circuit, it involves R279 a 47K resistor and R460 a 7.5K resistor. These two form a Voltage divider. What is helpful is that the scaled Voltage is 3.15V. So to trace it I just need to probe for 3.15V.

Here is the back of the board with the two resistors outlined:


Oh and yes I need to confess that I accidentally ripped up one of the pads on U24, which is in fact just a space for an IC. You can see the repair I made with some very thin enameled wire.

I have been probing all around the large IC for that 3.15V. Here you can see where it comes through to the top of the board via a, you know now via.


Attached to the red test probe is a push button in series with a 330Ohm resistor which goes to ground. So normally the red probe has just a 10MOhm impedance to GND which is the Digital Multimeter. When I push the test button a 330Ohm resistance to ground is presented.

like this:

(yes I know, probably would be quicker to draw a schematic on the PC than with a pen then scan it, LOL).

So if I connect the 24V to the board (without ramping it up slowly with the current limit control) the monitor does not initialize and the board draws a steady 60mA. If I touch the probe onto the 3.15V and push the test button the 3.15V becomes near 0V, then when I let go of the test button the monitor initializes and settles down to a steady current draw of 20mA. Then the monitor can be powered on and off with the proximity keypad!

So I've gone probing for a capacitor which has 3.15V across, but I just cannot find one. The PCB trace disappears underneath the large 416 pin BGA IC.

I could try adding a capacitor in parallel with R460, in fact there is space for one on the board(C337). But that is modifying not repairing, this monitor has worked fine for a few years, it should not need modifying.

[stj]

Re: Dell 2709w No power

could it use a faulty dallas reset ic - ds1233 for example?

[Neill]

Re: Dell 2709w No power

could it use a faulty dallas reset ic - ds1233 for example?

If only it were that simple! I do not see a reset chip anywhere.

Sure is a strange fault.

[ytsoc]

Re: Dell 2709w No power

Hello, i have one of these monitors, and i think it has the same fault.
Not sure i understood how yours manifests itself but mine does this:
I plug it in(power) and the power led comes on and that's it, it doesn't react at all.
Is there anything i can measure to help?

[Neill]

Re: Dell 2709w No power

Thank you for the offer of help.

So does the power LED come on briefly, or does it stay on? If it does stay on, is it blue or amber colored?

Does your computer recognize the monitor? Can you go into your display settings and see the monitor connected?

[ytsoc]

Re: Dell 2709w No power

from the moment i plug it in , the led is full blue and stays that way as long as it has power.
The monitor is recognized by the computer(via dvi) is idetified corectly and even the native resolution is ok.
There is a memory next to the heat sinked device(qfp one not the bga one) called 25lv020. If you can, replace it with a preferably blank new one.
I haven't gotten around to buy a new one to try it myself but i've had suggestions to this.

[Neill]

Re: Dell 2709w No power

What you describe sounds like the backlight is not working. With the monitor face down you can see some glow from the backlight, especially in a darkened room. Does your backlight work?

Do the proximity buttons respond to touch?

I have not heard of replacing the memory chip, not sure why this would help.

[ytsoc]

Re: Dell 2709w No power

Problem is that the monitor is completely unresponsive, i can't turn it off.
I have had experience with replacing similar memories but simptoms were a bit different

[stj]

Re: Dell 2709w No power

25lv020 is a flash chip.
if you fit a blank one it wont work - it has to contain the firmware.