Dell UltraSharp 2007Fp 2nd problem

[Radek]

I have Dell UltraSharp 2007Fp panel Rev A05 built Sept. 2008. I have successfully repaired this monitor couple of years ago by soldering open resistor. See attached photos.
No green or amber light when turned on. Nothing.

There is few threads going, but I am starting a new one as I understand this is the forum etiquette. Pardon me if I am wrong.

I removed all 4 boards and connected them tougheter. I found 19Volts going to USB board. Checked for 3.3Volt 5 Volt and 12Volt. Nothing. Rechecked previously installed resistor, all good there. Discovered 3Amp fuse blown. Soldered in 3Amp glass fuse.
When power was plugged in the 3 A fuse blew.

Since I have no schematic of the board and limited knowledge, I am hoping for some help.

There is a thread here https://www.badcaps.net/forum/showth...07fpb+teardown

With great photos and text. On a text notes it indicates “Monitor will work without USB Board installed”. On another thread I was reading (can not locate it now) that USB board must be connected for monitor to work. So I am confused.

Thank you all.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

One more measurement. Fuse to Ground short 1.5 Ohm.

[Per Hansson]

Re: Dell UltraSharp 2007Fp 2nd problem

Well you linked to an excellent thread on the matter.
Please check the diodes discussed there: FD3 and FD4

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Thanks for the enlightenment. FD3 and FD4 is all I needed, to wake up.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Not a good report.

Replaced pair of diodes FD3 and FD4 with new.

Did not like my large 2.7K resistor so I replaced that one as well.

Plugged it all tougheter and same thing 3A fuse blew.

Tried again with spare 3.5A fuse blew again.

Put back 3A new fuse and left the board by it’s self no other board connected.

Pulled up my adjustable power supply and fed 19V and the Ground to the respective pins
on the board, thinking maybe the short is in other boards.

No. The fuse blew again.

Can any good soul our there help me to find, how to locate this short ?

Thank you

[Per Hansson]

Re: Dell UltraSharp 2007Fp 2nd problem

Check Zener diode ZD701, also check the Mosfets.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Thank you. I am at work now. So I will get to it later.

I located the ZD701 and have to figure out how to test it, if I have to unsolder it or not, I am sure the answer is here somewhere as I was reading about the ZD here.
Mosfets, I think I located 4 of them on this board as I have it with me but will be able to look at this forum better when I get home. Need to figure out how to test them.

Thank again for pointing me in the right direction, appreciate your help very much.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

I unsoldered the zener diode ZD701. It is located just beside the 3 A fuse with my soldered on ugly big wires.
Diode is shorted according my ohm meter.
So I have looked for at least an hour over this forum and I am unable to find the rating so I can purchase one. All I found is one end has 3.3V and other goes to ground.
Can anyone please give me some numbers for this diode??

[Per Hansson]

Re: Dell UltraSharp 2007Fp 2nd problem

If the circuit voltage is 3.3v the Zener should be a bit above that, in this circuit it probably acts as a safety device for over voltage spikes.
I would say a 3.6v Zener might be a sensible value for ZD701
As you have desoldered it look for any markings on it, Zener diodes should be marked with a model number...

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Thanks for the reply.
Could not see any writing with my 30x loupe. I will see if I can get anything locally with 3.6V. Should I be concerned with Watt rating? I know it is only for spikes, so it will likely not need some huge capacity, but I am not experienced enough to judge.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

After I removed the zener diode, I powered on the board with 19V from the power supply.

New fuse did not blow. That is a good news. Some progress anyway.

Now the bad news is 3.3V reads 19V, 5V read 5V so that is OK and 12V reads Zero.

So that leaves me with identifying two bad components to get 3.3V and 12V. Not to be concerned about the 12V as I understand this is only for the speaker, but I will try to fix it anyway.

Back to the reading. If anybody can pinpoint this issue the better.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Valuable info from member "budm" should help me figure it out.
3) The 19v is also fed (J4) the USB Hub/3 Buck converter regulators (3.3V (Q6) for the Logic board where the VGA/DVI, control panel are, 5V (Q14) (this 5V is also fed into 3.3V linear regulator for the USB interface IC) for the 4-port USB hub (these 4 USB ports are protected by 4 fuses), 12V (Q9) for the powered speaker bar DC output jack. This 19V is fed through 3A fuse. MOSFETs Q6, 9, and 14 are 2SJ598, P-Channel.

[Per Hansson]

Re: Dell UltraSharp 2007Fp 2nd problem

Since the board is fed with 19v now you understand why the Zener failed, it tried to regulate that down to 3.6v or whatever it's rated for, obviously with a power rating of maybe 1/4w that did not work for very long
When it shorted out then you have a nice connection to the ground, thus the fuse blows...
The reason for the 3.3v being 19v is that whatever Mosfet is on that board to regulate that voltage is shorted too...

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Thank you for the guidance and coming back to answer.
Great learning curve. Watched video on YouTube how to remove the MOSFET.
It looked much easier in the video clip.
Anyhow, removed the Q9 MOSFET for 12V as I figured if I bugger that one all I am loosing is speaker power. Laid it out on a paper (courtesy of YouTube) and tested.
https://www.youtube.com/watch?v=mHpY_3tzJTc
Did 4 tests and it looked like failed the #3 test not switching “ON”.
So now I will order some of the 2SJ590 and replace Q9 for 12V and Q6 for 3.3V and Zener Diode 3.6V 500mW ±5% Surface Mount SOD-80 QuadroMELF.

[momaka]

Re: Dell UltraSharp 2007Fp 2nd problem

While at it, also get some good quality low-ESR quality caps to replace those Elite c[r]aps.
Buck regulators + crappy bad caps always = bad results.
Not saying that the caps are necessarily bad in your monitor. But it would be good to have the peace of mind that you won't have to open this monitor again and do the same repair when the caps go bad.

Laid it out on a paper (courtesy of YouTube) and tested.
https://www.youtube.com/watch?v=mHpY_3tzJTc
Did 4 tests and it looked like failed the #3 test not switching “ON”.

That's because the video shows a P-channel MOSFET being tested, whereas you most likely have an N-channel MOSFET.

To test N-ch FET basic "on" function, you put black (-) DMM probe on Source, touch Gate with red (+) DMM probe, and then put red (+) DMM probe on Drain. DMM should show a low resistance (if using a manual multimeter, use lowers resistance scale.) Now, if you short FET terminals with your finger (particularly, Gate to Source), and try to measure resistance between Drain and Source again, MOSFET should appear open (off) again.

*edit*
Sorry, I was wrong to assume you have an N-ch FET. According to budm's post in that thread, Q6, 9, and 14 are indeed P-ch FETs. But I suppose the above info is still good if you want to check an N-ch MOSFET, so that's why I left it there and didn't delete it with the edit.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Thanks nomaka.
Received all my parts, but unable to do anything due to my regular job interference.
I ordered all caps and will replace them as per your suggestion.
I will keep everyone informed as I go.
Thank You All.

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

While waiting for the parts, I stumbled on all 4 boards on eBay. So I ordered them all.

Finally I got a chance to replace 3 Mosfeds, ZD701 Zener, replaced FD3 and FD4 previously. Applied 19 Volts to the board and still did not get 3.3V and 12V where expected.

So I plugged all the boards tougheter and connected to monitor. Nothing.
Looks like job for rainy day.

Since I was tired of the mess, I installed the new USB board from eBay, still nothing.
Then I installed the used Logic board purchased from eBay at the same time. and put it together. Well I'll be darn, all lit up the way it is supposed to.

Anyway I assembled to monitor, no screws left over

And it has been plugged in and connected to PC for couple hours and all is well.

So unfortunately I have no magic to report, but as I am not all that good at these thing all I can say that Logic board was faulty, which caused the USB board not to function.

So now I will do more components replacement just to hone my soldering technique as it is atrocious.

Thank you all for being there.

[dicky96]

Re: Dell UltraSharp 2007Fp 2nd problem

HI Radek

Seeing as you are willing to learn, which is a good thing and less common than you might expect, please watch this video

https://www.youtube.com/watch?v=wRFRwOnLsZI

Do that and you will not be blowing any more fuses while repairing equipment, plus if you replace some parts and there is still another fault present you probably won't damage the new parts you fitted either.

This works very well for repairing power supplies and audio amplifiers in particular, I have found.

best regards
Rich

[Radek]

Re: Dell UltraSharp 2007Fp 2nd problem

Thank You “dicky96” for noticing my keen interest.
I will look at the video at the link you provided.

I will be repairing these 2 boards till I fix them or till I destroy them.
I will eventually come back and let every one know if I found the problem.

Thank you all, for your help.