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Old 08-25-2018, 01:42 PM   #541
Valetebellum
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Hello,
I got the exact same problem with various defective components on the board and want to try the external powering hsck by adrianm.
I read that instead of the supposed 19volt also somebady got it to work with a 24v power supply, which is 5v off.
So i'm hoping, that my 16v power supply with 5amps could also work, because it would only be off by 3volts.

I dont have the option off buying a 19v power supply online or in my surrounding area, so i either have to use the 16v power supply or dump the monitor into trash.


Sorry for not being able to do it the easy way, but any kind of response would be nice :-)
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Old 08-27-2018, 04:36 AM   #542
r-p
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Edit: nevermind... The guy using 24V was me and all my measurements were with my then faulty powersupply (since replaced the capacitor and it is fine again), so any measurement I did back then is untrustworthy. So I cannot answer your question.

Original answer before the edit:
I'll try to find my post, but I remember having tried several voltages (adjustable powersupply) after the hack. I cannot recall if I went as low as 16V.

It worked fine for years, but then someone posted a link to dirtcheap replacement powersupplies, I ordered one and it runs absolutely perfect on the new PSU. Do note it is only used occasionally at the moment, so I cannot vouch for it also working when used 24/7.

Since you have nothing to loose (apart from the probably quite well protected 16V supply), why not simply try it?

Not related, but just an example: I hacked a Dell external DVD drive caddy which should get 20V from the laptop. It came with a USB-plug with a different plug integrated into it, I chopped it off and replaced it with a normal USB cable and put 12V on the PCB where the 20V should go. It works perfectly. But that supply only steps down the 20V (and now the 12V) to 5V so that was quite easy and failsafe.

Last edited by r-p; 08-27-2018 at 04:48 AM..
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Old 05-28-2019, 08:34 AM   #543
Octoberon
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Lightbulb Re: Dell 2407WFPb Monitor - Bad Cap

I hope this may help somebody. I had a 2405FPW that was in a bad way.

Usual failure mode: Open circuit C605. Cascade failure ensues.

It is working now. There was some parts that were definitely bad, and some parts that tested OK. There were some parts that I just did not feel comfortable proceeding without replacing them.

Note: the attached circuit diagram is for a 2407. That said, the similarities between the 2405 and 2407 PSUs are very handy. Check my comments in the PDF to see what I found.

Good luck, these PSUs generally will work again with a little love.

Jon
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Old 08-03-2019, 09:34 AM   #544
sean0118
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by Octoberon View Post
Note: the attached circuit diagram is for a 2407. That said, the similarities between the 2405 and 2407 PSUs are very handy. Check my comments in the PDF to see what I found.
Thanks, the circuit diagram is really helpful.


I think there's actually a design issue. The feedback resistors for the boost circuit are 499k+232k+232k and 8.25k. The L6561 has a reference voltage of 2.5V. This will cause it to try to regulate to +294V DC.

2.5V *971.25/8.25 = 294V

But if you rectify 230V AC you get 325V DC, which is the input to this boost converter (and 30V higher than its output set point). Shouldn't the output be set to regulate at +400V DC? Or at least 350V?

It's 2am here so I might be missing something, but I don't see how this works with a 230VAC input.

Last edited by sean0118; 08-03-2019 at 09:43 AM..
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Old 08-04-2019, 05:37 AM   #545
sean0118
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Ah, never mind, I was wrong.

R666 (24.9K) gets put in parallel with R674. Which does make it regulate to 391V DC as would be expected.

So the design looks ok, the cap is just bad quality.
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Old 08-04-2019, 05:57 AM   #546
Octoberon
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Default Re: Dell 2407WFPb Monitor - Bad Cap

The Capacitor, C605, 120uF, 450V is definitely and by far the most common failure on these Benq made PSUs. It is so sad that the failure of this capacitor can be so catastrophic. Most of the failures I have seen, are where electrolyte has leaked out through a lead-hole in the rubber bung. The capacitors lead then appears to get etched away by the electrolyte.

Last edited by Octoberon; 08-04-2019 at 06:00 AM..
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Old 10-02-2019, 09:03 PM   #547
sean0118
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Default Re: Dell 2407WFPb Monitor - Bad Cap

I managed to fix mine as well.

I thought it wasn't fixed when I first tested it, because C605 only had rectified mains on it, not the ~400V DC expected if the PFC is boosting the voltage. But it turns out the PFC circuit doesn't turn on until it's connected to the other board, this is the signal "Power_off" which controls the optocoupler IC652.


I ordered all the parts from LCSC, but I'm sure Digikey/Mouser would have them too. There were some parts which aren't available anymore so I had to find a similar part to replace it with:

Designator - Original part on board - Replacement part
Q654 - 2N3906S - KEC 2N3906S-RTK/PS
IC651 - L6561D - ST L6562DTR
IC601 - NCP1200AD - ONsemi NCP1200D60R2G
D655 - LL4148 - ONsemi LL4148
D604 - LL4148 - ONsemi LL4148
Q651 - 2SK3502 - ST STF24N60M2
Q601 - 2SK3548-01SC - ONsemi FQA11N90C-F109
R670 - 0.22ohm - Futaba Elec RWS03JR220A750NH
R669 - 1K 0805 (0603?)
ZD652 - TZMC24 - TZMC24
C605 - 450V, 120uF - To save money I used a Nichicon part from a donor board for this, I think it was 100uF, but seems to work.

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Old 01-06-2020, 03:31 PM   #548
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Default Re: Dell 2407WFPb Monitor - Bad Cap

I hope this reaches you, Adrian. Thank you!

Got mine up and running with a new Lenovo laptop brick PSU (20V 4.5A 90W) that I picked up for about the equivalent of $15 USD. It barely gets warm.

I initially spent the past couple of weeks analyzing EVERY critter on the board right down to the SMD resistors many of which were out of tolerance. At least 52 components(MOSFETs, ICs, zeners, transistors, caps, resistors ... ) needed replacing due to severe cascade blowups in that dreaded "POOF!" from the oozin' 450V 'elite' cap, and I even had a shopping cart full of these items ready to order. Then I ran into this forum! Then Adrian's 'shortcut solution'.

The shopping cart's total for the components came out to be more than purchasing the new brick PSU mentioned above. And the thought of spending perhaps a few days soldering so many tiny SMD parts made me choose the more practical/cost effective/simple solution with the brick PSU.

I never liked the concept of an internal PSU anyways, as the substantial heat was always a concern for both the display as well as the PSU and other electronics. I had always thought that this great monitor would have been perfect with an external PSU... now it IS!

The monitor initially lasted me 12 years so I can't complain. 'Hope it lasts another 12 more!

Again, Thank you so much Adrian!
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Old 04-12-2020, 09:47 AM   #549
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Hello,
I'm trying to do the bypass procedure, but I'm a newbie as far as soldering is concerned. I've practiced with a soldering kit, but there was no example of soldering a cable to a pcb.
You will find a picture of what I've achieved so far. Of course it doesn't look professional at all, but could it work, or could there be a fire hazard?
Of course when I try to plug the power supply, I will have closed the full enclosure.
Thank you very much for your help.
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Old 05-05-2020, 10:53 AM   #550
DarkSupra
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Thanks AdrianM! Did the bypass mod as wel, always nice when you can easily fix something without buying anything.
Currently using a Hipro HP-OK065B03 adapter that i had laying around.
Its 19v 3.43A 65W
It gets pretty warm but so far it's working fine on a whole day of use.
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Old 05-12-2020, 03:37 AM   #551
r-p
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by gillesMa View Post
You will find a picture of what I've achieved so far. Of course it doesn't look professional at all, but could it work, or could there be a fire hazard?
The lower soldering has clear separate strands visible. I'd like to see a nice smooth blob of solder cover them and keep them together. But I think it will be OK, I'm just nitpicking.

Yours looks, imho, a little but like the second or third solderjoint in the pic below.
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Old 06-23-2020, 03:39 PM   #552
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Funny thing, I had the 2405 running day and night for 15 years with no problems.
But the 12 year old 2407 I have was the one failing after only 3 days use after it was not used for the last 5 years.
Both where standing in the same room at the same desk all the time.
Another funny thing is that they have almost the same power supply and with the same capacitors.
Anyway, I found a suplier in China that have them in stock here: https://www.abctay.com/dell-4hl2k02a...fp-p-1631.html

I ordered one to have spare at 13 USD, but I see the price now 2 days later have gone up. The shipping is a little expensive, but if they will drop the price again it is worth it.

I will regardless of that repair the broken one tomorrow, but then I at least have a spare.
The parts from farnell was with shipping ending at the same price as the new part from China at 42 USD.
But then the parts was arriving the day after I ordered it, and the shipment from China will take about 1 - 2 weeks with DHL if nothing gets in the way.
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Old 06-29-2020, 03:59 PM   #553
r-p
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Default Re: Dell 2407WFPb Monitor - Bad Cap

Quote:
Originally Posted by r-p View Post
.... then someone posted a link to dirtcheap replacement powersupplies, I ordered one and it runs absolutely perfect on the new PSU. Do note it is only used occasionally at the moment, so I cannot vouch for it also working when used 24/7.
Still going strong, being used as gaming monitor by my son a few hours a week.

I did notice the 230V~plug being finicky. A Display-Port-to-DVI converter worked fine the first day, but did not work at all the second day. When replacing it with a DVI-DVI cable in a very confined space, the monitor would turn off several times when touching the powersupply-plug going into the monitor even though it was securely mounted. Afterwards it worked fine, so the DVI-input on the Dell was not the problem.
But since this 14$ board is no longer available through the Aliexpress seller, this is useless info... If I ever open it up again, I'll check for weak soldering joints.

Only way I can get hits on the powersupply now is with the modelnumber : 4H.L2K02.A01. But the hits are limited to (expensive) used boards.

Last edited by r-p; 06-29-2020 at 04:00 PM..
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