Dell 2407wfpb

[clark97]

Re: Dell 2407wfpb

Check SMD resister R669 should be 1k ohm was open on mine and would cause another blow.

[jetadm123]

Re: Dell 2407wfpb

IC651- L6561D
Q654- mmbt3906

[dssuman]

Re: Dell 2407wfpb

Dell 24 inch that appears to be previously "repaired". It shows no signs of power (The main fuse is good but i get no power lights, sounds or video and the backlight does not turn on.) The main cap is different, not sure that they replaced it with the correct value. Does anyone know what the correct value is for the main cap? I purchased and build the blue esr meter, all the caps appear to be good, so im not sure where to start

Hi I found burning in IC651 and Q654 transistor in power board of Dell 2407wfp. Please can you let me know the part no of these?

[newbie1]

Re: Dell 2407wfpb

The 'popping' is easy to explain if you look at a schematic of a SMPS. The positive side of the 165VDC (or higher) across the mains cap is tied to one end of the primary of the SMPS. The other end of the primary is tied to the drain pin of the power FET. The source pin of the power FET is tied to one end of the .22 ohm resistor. The other end of the .22 ohms resistor is tied to the negative side of the mains cap. IF the FET is shorted, that resistor is seriously overstressed and will pop.

The best way to make sure nothing will pop is to replace the power FET, the resistor, and the SMPS controller. Check all diodes in the area, then current limit the primary voltage by inserting a 40 watt light bulb in series.

PlainBill

..aye aye captain..

not sure whether i can get hold of a new SMPS controller. but will try to order the FET, resistor & fuse first & perform the 'light bulb test'...... but would not be so soon though..

[knoxrebel]

Re: Dell 2407wfpb

Yep, Shorted in all three measurements. Under .5 ohm.

[newbie1]

Re: Dell 2407wfpb

Newbie, was your monitor repaired, then the resistor and fet failed? Or did all the components fail at the same time.

This was what happened when i received the faulty monitor,

Model : Dell 2407wfp

Failure : No power LED. Owner claimed that upon switching ON the Power switch a Pop sound was heard + burning smell coming out of monitor.

Dissambled it and I can see that one of the leg of the Big cap is almost/already broken. 2 pink resistors got burnt. Proceed to measure some of the components & found out that
1) Main Fuse open
2) Bridge rectifier shorted
3) Transistor Q601 shorted
4) Transistor Q651 shorted

After replacing the above, like for like, except Q651 (see earlier post), the 'POP' thing happened.

After that i measured the components again & now i got
1) Main Fuse open
2) Bridge rectifier NOT shorted
3) Transistor NOT Q601 shorted
4) Transistor Q651 shorted
5) 0.22ohms near Q651 is burnt
6) 0.22ohms near Q601 is NOT burnt. tested within range.

Hope i am not confusing anybody here. ..

I was wondering whether there is another component that we missed out that is causing the sense circuitry resistor to blow. From my ONE & only past experience with this resistor getting burnt, is caused by a bad connection on one of the poly capacitor leg beside the resistor on a power supply of a samsung TV. See thread here. But the mystery continues with this Dell 2407wfpb power board though.

[PlainBill]

Re: Dell 2407wfpb

Somehow i sense a feeling of dejavu. & i think the guys in this thread are experiencing the same 'POP' incident as well.

Somewhere in May, i did replaced Q651 (orginally 2SK3502) with MOSFET FCPF11N60 together with the filter cap, burnt resistors, etc as per my previous thread. And it turn out that once i plugged the monitor, the 0.22ohm sense circuitry resistor did the same 'POP' to me. I have measured my newly replaced FCPF11N60 MOSFET & it turn out that all G-D-S are shorted. So i am guessing yours will be shorted as well.

I have yet to proceed to order the MOSFET 2SK3502 because in my area the only MOSFET close the specs is 2SK3501.. Hope someone can crack the code on why is the 0.22ohm sense circuitry resistor keep 'popping' upon plugging in.

EDIT : or maybe i should try replacing 2SK3501 at Q651 (which will be delivered wihtin 1-2weeks) & see whether 0.22ohm will still 'pop'?..

The 'popping' is easy to explain if you look at a schematic of a SMPS. The positive side of the 165VDC (or higher) across the mains cap is tied to one end of the primary of the SMPS. The other end of the primary is tied to the drain pin of the power FET. The source pin of the power FET is tied to one end of the .22 ohm resistor. The other end of the .22 ohms resistor is tied to the negative side of the mains cap. IF the FET is shorted, that resistor is seriously overstressed and will pop.

The best way to make sure nothing will pop is to replace the power FET, the resistor, and the SMPS controller. Check all diodes in the area, then current limit the primary voltage by inserting a 40 watt light bulb in series.

PlainBill

[knoxrebel]

Re: Dell 2407wfpb

Newbie, was your monitor repaired, then the resistor and fet failed? Or did all the components fail at the same time.

[knoxrebel]

Re: Dell 2407wfpb

Im pretty sure that the fet is shorted, but ill check in the morning when i get back to my bench.

[newbie1]

Re: Dell 2407wfpb

Somehow i sense a feeling of dejavu. & i think the guys in this thread are experiencing the same 'POP' incident as well.

Somewhere in May, i did replaced Q651 (orginally 2SK3502) with MOSFET FCPF11N60 together with the filter cap, burnt resistors, etc as per my previous thread. And it turn out that once i plugged the monitor, the 0.22ohm sense circuitry resistor did the same 'POP' to me. I have measured my newly replaced FCPF11N60 MOSFET & it turn out that all G-D-S are shorted. So i am guessing yours will be shorted as well.

I have yet to proceed to order the MOSFET 2SK3502 because in my area the only MOSFET close the specs is 2SK3501.. Hope someone can crack the code on why is the 0.22ohm sense circuitry resistor keep 'popping' upon plugging in.

EDIT : or maybe i should try replacing 2SK3501 at Q651 (which will be delivered wihtin 1-2weeks) & see whether 0.22ohm will still 'pop'?..

[jetadm123]

Re: Dell 2407wfpb

With your power supply unplugged, set your meter to resistance and place your probes as follows: G-S, G-D and D-S. If any of the measurents show near zero ohms, you have a short.

[knoxrebel]

Re: Dell 2407wfpb

Not sure how i should test this mosfet. The gate, drain and source are labeled
.

Mosfet is Q651

[jetadm123]

Re: Dell 2407wfpb

Good catch by newbie1. At this point, you might want to check the heatsinked mosfet (Q65??) to the right of that .22 ohm resistor for shorts.

[knoxrebel]

Re: Dell 2407wfpb

Well, as soon as i replaced the resistor .22 with a 3w .22 ohm resistor and plugged back in the power the resistor popped and let the smoke out.


...Yet again I am brought to believe that electronics run on smoke.

[knoxrebel]

Re: Dell 2407wfpb

That resistor that was replaced is dead. I have just replaced it with a spare 3w that i had.

[PlainBill]

Re: Dell 2407wfpb

Thanks for the heads up on resistor r670, i can tell by the way that the leads were cut and soldered that it was replaced after the fact. Not sure if this would cause a problem though.
R603 is the one that is discolored, it was removed and tests good.
IC601 pin 6 I get 0v and pin8 i get 56v

A .22 ohm resistor would typically be used to sense current through the power FET. Changing that to 2.2 ohm is going to cause problems.

The voltage at pin 8 is unusually low, but is within specs. The voltage at pin 6 indicates there is a problem with the NCP1200 or the cap tied to pin 6.

PlainBill

[knoxrebel]

Re: Dell 2407wfpb

Thanks for the heads up on resistor r670, i can tell by the way that the leads were cut and soldered that it was replaced. Not sure if this would cause a problem though.
R603 is the one that is discolored, it was removed and tests good.
IC601 pin 6 I get 0v and pin8 i get 56v

[newbie1]

Re: Dell 2407wfpb

OP, i would like just to share as i have a similar power board, which is still waiting for my lazy bum to get going, and to get the CORRECT replacement parts. .

The main filter caps of my board is Elite PW(M) 120uf 450V. I believe this is the original capacitor & value as i had opened up 2 of these monitors & in them the same cap is the one failing.

Just another observation. I noticed that R670 in your repaired power board is of different color coded as mine. Mine (originally was there & burnt) is Red-Red-Silver-Gold (0.22ohms +/-5%). Yours (i guess it was replaced) is Red-Red-GOLD-Gold (2.2ohms +/-5%). However, i am not expert enough to tell whether the difference will cause it to malfunction as what your monitor is behaving.

Let me know if u need any resistance measurement as i have not yet assembled my monitor yet.

[PlainBill]

Re: Dell 2407wfpb

After you answer jetasdm123's questions, I have a couple of points to check.

Pin 4 of IC601 is ground; use that for the following measurements: What are the voltages on pin 6 and on pin 8 of IC601?

PlainBill

[jetadm123]

Re: Dell 2407wfpb

Looks like IC651 is a L6561D power factor corrector chip and IC601 is a NCP1200 SMPS controller chip.

Out of curiosity, the resistor I mentioned in post #6, does it's measured value come close to the color bands on the resistor itself? You may have to lift one end of the resistor off the board in order to measure an accurate value. And is it labeled R603? Also, is one end of this resistor connected to any of the legs of IC601? If yes, which one?