Dell 2407WFPb Monitor - Bad Cap

[dogletico]

Re: Dell 2407WFPb Monitor - Bad Cap

This is not going to be easy!
Can you post good clear pictures of your boards.
When it "locks" do you mean
1 picture stays on
2 screen goes blank power led stays on
3 screen goes blank power led goes off
4 screen goes white.

OK.
On the PC (VGA), after about 30 minutes, the screen goes black, the LED on and dead controls.
Connected to a satellite receiver (TV) (VIDEO) after about 30 minutes, the screen is with mixed colors and illuminated LED controls and dead.
Turning off the power on again and everything back to normal until locked again.
Post photos later.
Grateful.

[selldoor]

Re: Dell 2407WFPb Monitor - Bad Cap

This is not going to be easy!
Can you post good clear pictures of your boards.
When it "locks" do you mean
1 picture stays on
2 screen goes blank power led stays on
3 screen goes blank power led goes off
4 screen goes white.

[dogletico]

Re: Dell 2407WFPb Monitor - Bad Cap

Hello friends.
Won by a monitor 2407WFPb is defective and friend who gave me could not waste time on concert.
Well, ask experts to help this wonderful Forum.
Here is what I noticed in the defect:
Perfect operation, image and fully operational controls, but after 30 minutes, she literally "LOCK". Turns off the power and turns the power on and it starts normally and back to work for another period.
I opened the monitor and visually saw no fault in the components.
I suspect there might be some problem with the "Firmware".
I leave here so this case to analyze.
Hugs.
Ps: Sorry for my English, I'm using a translator.

[selldoor]

Re: Dell 2407WFPb Monitor - Bad Cap

Ok - Good luck
Its always useful to report back as it may help others in the future.

[aschi-ch]

Re: Dell 2407WFPb Monitor - Bad Cap

I did not find that russian site so far - thanks!
On my board, C628 is a fair bit 'higher' (or thicker) than (what remained of) c626.
Anyway i measured C628 - it's 1uF.

R669 and C626 form an RC-Lowpass for the current-feedback,
currently i don't know the switching-frequency, but 1microfarad seems to be to much:
R669 is 1k, so the filter has a Frequency of 195Hz, which i think is to low, since the switching-frequency is probably somewhere around 10kHz.
I think i will try with ~1-10nF (159kHz - 15.9kHz).

In the meantime i found the Application-Note AN966 from ST.
There i can find one circuit example, where they have a filter in the feedback-path.
There they have 330Ohms and 1nF Capacitor.

You will get a feedback when i replaced all the failed parts, but i have to order them first.
And befor i can order, i have to finish the BOM of another Project, because i want to order all parts together.
So it could take some time till i have any feedback.

[selldoor]

Re: Dell 2407WFPb Monitor - Bad Cap

I cant find any reference to it as being faulty but on this russian site
http://monitor.espec.ws/section33/post1216836.html

there is a clear picture of it and is is on their wiring diagram.

If it doesnt work without it C628 looks to be the same size and if you have any facility to measure that, perhaps try one the same value.

Unless anyone comes up with a definitive reply.

[aschi-ch]

Re: Dell 2407WFPb Monitor - Bad Cap

Yes, ok.
No, unfortunately there are no markings.
It is a standard SMD case, probably 0805 size.
Voltage would be verry low, this cap goes from Pin 4 of the L6561 to Ground.
Pin 4 is the current-feedback-voltage, measured by the famous R670, which is 0.22Ohms.
I would assume that this cap is around ~10nf, it is just to filter the current-feedback.
On the Typical Application Circutis in the datasheet of the L6561, there is no capacitor in that position,
maybe it works even without...

[selldoor]

Re: Dell 2407WFPb Monitor - Bad Cap

Sorry I did try to find a pic but couldnt see one.
Re there no markings on it - The physical size is also a clue.
If you have made out a schematic do you already know the voltage?

[aschi-ch]

Re: Dell 2407WFPb Monitor - Bad Cap

Thank you.
Yes it is the same board, but unfortunately there are only the Electrolytic caps listed.
C626 is an SMD ceramic cap.

[selldoor]

Re: Dell 2407WFPb Monitor - Bad Cap

Looks like this is a list of caps (IF YOUR board is the same) so you can work out
which it is by elimination

https://www.badcaps.net/forum/showpo...2&postcount=33

[aschi-ch]

Re: Dell 2407WFPb Monitor - Bad Cap

I am currently working on a Power-Supply of a 2407WFPb.
Trough the help of you in this awesome Forum, i was able to find replacement-Parts for all dead components on my board, with exception of one:
On my board, C626 is dead as well. Does anyone know, what capacity C626 is?
Would be great to have more information on that.

btw:
If anyone needs more inforamtion about this board:
I have drawan the complete scematic of that board (currently only by hand as a draft) by following the traces and mesaunring the components.
Now i am adding all known information of all the Parts (Ratings, values, replacement-parts etc.)

[danfisch]

Re: Dell 2407WFPb Monitor - Bad Cap

Are the PSU boards for the 2405 and 2407 boards interchangeable? There seem to be a lot of 2407 boards floating around on ebay / taobao, whilst the 2405's are a bit thin on the ground. The connectors mark CN701 (to logic board) and CN702 (to inverter) look identical in terms of dimensions and wiring colours.

[braxton]

Re: Dell 2407WFPb Monitor - Bad Cap

my 2405 seems to be in standby mode and does not switch over to "on".
Is there a way to bypass the on-off switch or test it at the board?

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

The reason it does not work may due to the sub-power supply board has the problems, there are buck regulator circuits that convert the 19v to lower voltages that you need to check.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[Misterkeeks]

Re: Dell 2407WFPb Monitor - Bad Cap

Has anyone got this mod to work on the 2405? I tried this mod with a 19V 4A power supply and still no power???

I too would like to know this. Considering trying it, seems easier than troubleshooting.

[braxton]

Re: Dell 2407WFPb Monitor - Bad Cap

Has anyone got this mod to work on the 2405? I tried this mod with a 19V 4A power supply and still no power???

Also, does this mod replace the need to use the power on/off button on the 2405? The reason I ask is that I'm beginning to suspect that I am having a power on triggering problem with the power switch.

How can I bypass the power on button switch on the main board itself?

[braxton]

Re: Dell 2407WFPb Monitor - Bad Cap

Tyan, the speaker socket/power mod is a simple three-step process:

1) In the photo attached below I have marked both ends of L702, which is to be removed from the PCB, with magenta crosses. De-solder or just cut both ends of this inductor (a bit of wire that passes through a ferrite bead on the component side). This isolates the power socket from it's normal supply circuit.

2) The short blue line shows where to solder a bridging wire to permanently ground the switched contact for the socket CN703 - making it seem that the speaker isn't plugged in. A blob of solder across C718 would also do the trick.

3) Run a decent gauge stranded, insulated wire between the points marked with an orange line. To get a good solder joint on the land between C713 and F701 scrape away the lacquer first. The other end of this wire goes down onto the middle pin of socket CN703 which is already quite well exposed for soldering.

That's really all there is to it! The central pin in the speaker socket may be a little smaller than the power-brick plug (2.1mm vs 2.5mm I think) If it doesn't connect very well, it might be necessary to roll a small piece of copper or tin shim to increase the diameter of the centre pin. If that's too fiddly then you can always swap the socket for the correct sized one, or find an adaptor lead. I slipped a slender wire crimp insert over the pin which worked a treat.

Has anyone got this mod to work on the 2405? I tried this mod with a 19V 4A power supply and still no power???

[rocket]

Re: Dell 2407WFPb Monitor - Bad Cap

Thanks to this board I have managed to repair my 2405. Many thanks to the contributors. I had the usual initial failures:
R670 (blown - replaced by cheap metal film 2W off ebay)
C605 (blown - replacement sourced from ebay again)
IC651 L6561D (destroyed - replaced over ebay)
Q651 SK3502 (shorted pins on testing - replaced via ebay)

Oddly the fuse was still intact but the monitor did not power on.

Then replaced:
IC601 NCP1200D (from RS couldn't wait!)
ZD601 15V 0.5W zener from local shop

Fired up perfect!

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

What is the IC designator, IC651?

[arber]

Re: Dell 2407WFPb Monitor - Bad Cap

Put your meter in diode mode and check to see if it is still tested out like Diode.
http://s807.photobucket.com/user/bud...?sort=3&page=1

plzz tell the number that blcak little chip i cant see