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Old 09-29-2011, 08:56 AM   #101
thewzard
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Default Re: Dell 2407WFPb Monitor - Bad Cap

I'm going to purchase a multimeter for next week when I attempt to repair this little bad boy. Anyway, the real question is: once I have a multimeter how do I use it?

I put one lead on one end of the cap/resistor/etc and the other lead on the other end and the screen should read what? And I assume I can do this with all parts I suspect to be bad or are there special instructions for certain pieces? Lastly, if the capacitor is standing and i can't measure from the top, I can flip the board around and use the same endpoints on the bottom of the board to get the read correct?
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Old 09-29-2011, 09:25 AM   #102
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Default Re: Dell 2407WFPb Monitor - Bad Cap

you should find instructions to test the single parts by query google for "check transistor" (e.g.).

what you can do easily with the multimeter on "beep"-setting (makes a beep if theres no/very little resistance in the part. Marked with some kind of speaker symbol):

Transistor
check all possible three combinations of the "foots", if anyone beeps -> broken

Diode
in both ways beep (switch the needles) -> broken

Fuse
no beep -> broken

Cap
possible, but i donīt know how. The multimeter has to have a special function for this. I donīt even know if mine is having it.

Resistance is easy, when you know, with value it should have. If the multimeter tilts on highest range, its broken

You can turn the PCB around and test on the endpoints, yes. All checks on unplugged board!
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Old 09-29-2011, 10:00 AM   #103
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Thats just what I needed to get started. Thanks!
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Old 09-29-2011, 01:55 PM   #104
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Default Re: Dell 2407WFPb Monitor - Bad Cap

ok, now iīve changed the 120uF cap (to a 150uF 400V 105°), the resistor, the 3502 MOSET (to a P10NK60Z) and the fuse.

After plugging in an switching on (the power board alone) there was a really beautiful blue-white flash and than i sat in the dark (it is nearly 9PM here).

the fuse melted, but the new parts are still ok. So i guess here the real challenge begins...

edit:
i just talked to my uncle who is an absolute professional in e-technics (designing & building his own hifi amps for fun e.g.) and he told me two things:
- itīs nearly sure that the real problem lies within the trafo (one of those coils), and itīs nearly impossible to find replacement
- buy a new monitor

my work ends here. iīll put the pieces in a box and search the internets again in 6 months or so. If nobody found a solution until then (or new power boards pop up somewhere) the whole box will face itīs final destination.

Last edited by Tyan; 09-29-2011 at 02:19 PM..
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Old 09-29-2011, 06:21 PM   #105
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by Tyan View Post
ok, now iīve changed the 120uF cap (to a 150uF 400V 105°), the resistor, the 3502 MOSET (to a P10NK60Z) and the fuse.

After plugging in an switching on (the power board alone) there was a really beautiful blue-white flash and than i sat in the dark (it is nearly 9PM here).

the fuse melted, but the new parts are still ok. So i guess here the real challenge begins...

edit:
i just talked to my uncle who is an absolute professional in e-technics (designing & building his own hifi amps for fun e.g.) and he told me two things:
- itīs nearly sure that the real problem lies within the trafo (one of those coils), and itīs nearly impossible to find replacement
- buy a new monitor

my work ends here. iīll put the pieces in a box and search the internets again in 6 months or so. If nobody found a solution until then (or new power boards pop up somewhere) the whole box will face itīs final destination.
With all respect to your uncle, he is almost certainly wrong. A failure of the SMPS transformer is very, very rare. It is much more likely the problem is the SMPS controller, or one of the components associated with the drive signal to the power FET.

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Old 09-30-2011, 01:33 AM   #106
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Default Re: Dell 2407WFPb Monitor - Bad Cap

referring to the other thread about this problem you think its the IC601 shown in this pic?



this one looks factory new on my board... but nevertheless, if somebody could tell me, where i get one of these NCP1200A60-200A6 iīll give it a try!

anyway iīll buy a new monitor

Last edited by Tyan; 09-30-2011 at 01:35 AM..
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Old 09-30-2011, 06:49 AM   #107
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by Tyan View Post
referring to the other thread about this problem you think its the IC601 shown in this pic?


this one looks factory new on my board... but nevertheless, if somebody could tell me, where i get one of these NCP1200A60-200A6 iīll give it a try!

anyway iīll buy a new monitor
The NCP1200A is available on eBay for under $6.00, including shipping. The L6561D is also available from the same seller, and at the same net cost.

If the one on the board does in fact have a hole in the top, that would explain the fuse blowing. I STILL don't have a good handle on the operation of the PFC circuit, but looking at figure 7 of the datasheet, the FET is directly across the rectified mains voltage. When the resistor blew, the L6561D would take the hit.

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Old 09-30-2011, 08:24 AM   #108
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Default Re: Dell 2407WFPb Monitor - Bad Cap

this is a bit too much for my electronic knowledge :-/ iīll see if i can get them via eBay, fumble them on my board and then letīs see, if that helps. Should have bought more fuses, only 1 left :-/
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Old 09-30-2011, 12:03 PM   #109
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by Tyan View Post
this is a bit too much for my electronic knowledge :-/ iīll see if i can get them via eBay, fumble them on my board and then letīs see, if that helps. Should have bought more fuses, only 1 left :-/
One trick I use in situations like this is to replace the fuse with a incandescent light bulb. If the light bulb comes on and glows brightly, something is shorted. If it flashes bright for a second, then glows dimly, there is no short.

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Old 09-30-2011, 02:26 PM   #110
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Default Re: Dell 2407WFPb Monitor - Bad Cap

thanks for that light bulp trick!

iīve ordered them both via eBay in china. Theyīre 3,90$ each + 3$ shipping btw. and ~20 days delivery til theyīre here in germany...
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Old 10-04-2011, 10:33 AM   #111
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Default Re: Dell 2407WFPb Monitor - Bad Cap

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Originally Posted by newbie1 View Post
It seems like my faulty power board has more faulty components then those stated in Post #77. I tried to purchase the whole board from Taobao.com, as being shared above, but they are ALL out of stock. So back to ordering & replacing the faulty components one-by-one..

Now I need your help, guys!!..

In addition to post #77, i had another SMD resistor R623 faulty as well.. I think it is tied to one of the leg of Q601 (shorted as well). But the problem is i could not see clearly the marking on it. Kindly see the attachments.. From what i can tell it is 4(?)7.. But i can't be sure. SO, i will need some expert help what the resistance i should order to replace the burnt resistor.. I have not yet completely check the rest of the zeners/diodes.. Hopefully, there would not be more being 'shot'.
update.

Replaced both LD6561D & NCP1200D, together with
1) C605 120uF/450V
2) Q651 STP10NK60ZFP,
3) R669 1k ohms SMD
4) Q601 2SK3548
5) ZD601 15V 0.5W Zener diode
6) R623 4.7ohms (4R7) SMD
7) R670 & R615 (0.22ohms)

Did the 'bulb test'. It light up for a fraction & goes-off... Ok good, so i thought.. Smelling success, here...

Replaced the Main Fuse. Hit the Power switch. DA*N IT!! IT DOESN'T light up. Sigh!. But the good thing is the 'popping' of the resistor has stopped.

So back to square one. Upon measuring some of the diode, found out that Q654 pins C-B-E are all shorted to each other (0 ohms). Pin C is tied to a capacitor linking to the Pin 8 (VCC) of the L6565D. But i am not sure what type of diode it is..
What i can see on the top of the Q654 is marked ZA with a 16 or 9L at the side (not really sure though). Package width is approx 3mm. Pictures attached

Any thoughts what it is?..
Attached Images
File Type: jpg DSCF4262.jpg (354.2 KB, 260 views)
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Old 10-04-2011, 12:48 PM   #112
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by newbie1 View Post
update.

Replaced both LD6561D & NCP1200D, together with
1) C605 120uF/450V
2) Q651 STP10NK60ZFP,
3) R669 1k ohms SMD
4) Q601 2SK3548
5) ZD601 15V 0.5W Zener diode
6) R623 4.7ohms (4R7) SMD
7) R670 & R615 (0.22ohms)

Did the 'bulb test'. It light up for a fraction & goes-off... Ok good, so i thought.. Smelling success, here...

Replaced the Main Fuse. Hit the Power switch. DA*N IT!! IT DOESN'T light up. Sigh!. But the good thing is the 'popping' of the resistor has stopped.

So back to square one. Upon measuring some of the diode, found out that Q654 pins C-B-E are all shorted to each other (0 ohms). Pin C is tied to a capacitor linking to the Pin 8 (VCC) of the L6565D. But i am not sure what type of diode it is..
What i can see on the top of the Q654 is marked ZA with a 16 or 9L at the side (not really sure though). Package width is approx 3mm. Pictures attached

Any thoughts what it is?..
ZA crosses to a diode. 2A is a 3906 equivalent PNP transistor. Information is here (follow the Marking SMD link).

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Old 10-04-2011, 02:17 PM   #113
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Default Re: Dell 2407WFPb Monitor - Bad Cap

yep, same here. And the "big" Cap next to it (C620) is also toast.
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Old 10-04-2011, 03:12 PM   #114
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Just go 3 pages back, the solution is there for you!
http://badcaps.net/forum/showpost.ph...3&postcount=77
I did those steps on a 4H.L2K02.A01 board, and it's working now! Had the same problems with the burned resistor. Thanks's btw endor!!!! Had to order the parts but it works like a charm, now.
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Old 10-05-2011, 05:59 PM   #115
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by PlainBill View Post
ZA crosses to a diode. 2A is a 3906 equivalent PNP transistor. Information is here (follow the Marking SMD link).

PlainBill
Thanks PlainBill!. Splendid website!!.. I wish i could say the same for my current repair though.

Update. Replaced the shorted SOT23 diode with a MMBT3906 (PDF attached). No joy! I measured 330V across the Big cap. But NO voltage output to the other card (Logic or inverter). I will TRY to flip over & measure voltages on the NCP1200D & L6565D (PDFs attached). If anybody could point out which particular pins on them i should be focusing on, that would be great!.

Quote:
Originally Posted by Tyan View Post
yep, same here. And the "big" Cap next to it (C620) is also toast.
Tyan, may i know how do you tell it is toast? Visually, I can't see anything wrong with it. But i do not have a capacitance measurement to measure it though.
Attached Files
File Type: pdf mmbt3906_f.pdf (97.5 KB, 163 views)
File Type: pdf ncp1200d.pdf (138.7 KB, 108 views)
File Type: pdf l6565d.pdf (246.4 KB, 94 views)
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Old 10-05-2011, 06:52 PM   #116
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Default Re: Dell 2407WFPb Monitor - Bad Cap

I have not been following this thread, so I don’t know if this will pertain to yours of not.
I am working on this model at the moment. One thing I have noticed is the monitor will not work unless the USB card is hooked up.
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Old 10-05-2011, 09:19 PM   #117
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by newbie1 View Post
Thanks PlainBill!. Splendid website!!.. I wish i could say the same for my current repair though.

Update. Replaced the shorted SOT23 diode with a MMBT3906 (PDF attached). No joy! I measured 330V across the Big cap. But NO voltage output to the other card (Logic or inverter). I will TRY to flip over & measure voltages on the NCP1200D & L6565D (PDFs attached). If anybody could point out which particular pins on them i should be focusing on, that would be great!.



Tyan, may i know how do you tell it is toast? Visually, I can't see anything wrong with it. But i do not have a capacitance measurement to measure it though.
On the power supply, I suggest you try to see if you can measure the 5V standby voltage on the wiring harness with all the black wires. Unfortunately, there are no voltage labels on this board. If you measure the 5V, try measuring the Vcc voltages for the L6565 and NCP1200 controller chips.
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Old 10-06-2011, 07:32 AM   #118
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Default Re: Dell 2407WFPb Monitor - Bad Cap

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Originally Posted by newbie1 View Post
Tyan, may i know how do you tell it is toast? Visually, I can't see anything wrong with it. But i do not have a capacitance measurement to measure it though.
ummm, it has nearly 0 resistance. But meanwhile iīve read endors post and had to learn that this doesnīt have to mean itīs dead. It also can be, that thereīs a short between the connected parts... so i have to admit: my statement may be wrong.
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Old 10-08-2011, 09:00 PM   #119
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by jetadm123 View Post
On the power supply, I suggest you try to see if you can measure the 5V standby voltage on the wiring harness with all the black wires. Unfortunately, there are no voltage labels on this board. If you measure the 5V, try measuring the Vcc voltages for the L6565 and NCP1200 controller chips.
*this is getting messy.

I manage to flip the Power board over & ground it. Measured 0V on ALL the pins with respect to Gnd on CN701 & CN702. Also I managed to measure the pins on the L6565 & NCP1200 with respect to the -ve pin of the Big Cap.

L6565
Pin 1 (INV) - 2.10V
Pin 2 (COMP) - 0.12V
Pin 3 (VFF) - 2.43V
Pin 4 (CS) - 0v
Pin 5 (ZCD) - 0v
Pin 6 (GND) - NA
Pin 7 (GD) - 0.1V
Pin 8 (VCC) - 1.15V

NCP1200
Pin 1 (ADJ) - 0.39V
Pin 2 (FB) - 4.5-4.7V (UNSTABLE)
Pin 3 (CS) - 0.76V
Pin 4 (GND) - NA
Pin 5 (DRV) - 0-0.5V (UNSTABLE)
Pin 6 (VCC) - 6.97-9.35 V (UNSTABLE)
Pin 7 (NC) - NA
Pin 8 (HV) - did not dare to measure because Max volt=500V! hee..

So, I proceeded to check SOME other points on the power board from the Big cap (measured 326V) onwards down to the ICs, to find out why the VCC is low for both ICs. Then something STUPID & BAD happened.

I measured 326V on Pin 2 (DRAIN) of Q651 with respect to Gnd. But got 0V on both the Pin 1 (Gate) & Pin 3 (SOURCE). The I move the probes to measure voltage between Pin 1 (Gate) & Pin 3 (SOURCE), which is VGS. A SPARK, small FIRE & MAGIC SMOKE coming from Pin 8 (HV) of NCP1200!. Also MAGIC SMOKE coming from the other side near T601!!. I quickly unplugged the main Power. When I flipped the board over R603, linking to Pin 8 (HV) of NCP1200 is visibly burnt. So, again, I need the help from you guys.

1) Could someone, with the same board, identify R603 so i could replace it? I think NCP1200 will be needed to be replaced as well, right? Sigh!
2) Did measuring VGS of Q651 a WISE thing to do? Will it caused the SMOKE, FIRE & BURNT? or is there something else which i missed out?

what a way to start your Sunday..
Attached Images
File Type: jpg DSCF4266.jpg (367.6 KB, 122 views)
File Type: jpg DSCF4267.jpg (304.4 KB, 136 views)
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Old 10-09-2011, 10:46 AM   #120
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Default Re: Dell 2407WFPb Monitor - Bad Cap

thats mine, reading
brown black orange yellow



should be 10k ohm, mine has 9,85k
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