DELL 2405fpw

[dankva]

@carbonosilicio: My original D19 was 6.2 V.

I've been a long time lurker in this forum and I'm grateful to find such an admirable community of skilled technicians, engineers, and hobbyists.

I have a 20 years old Dell 2405FPW monitor that decided to stop working recently. I'm posting today a partial circuit that helped me to diagnose the faulty monitor, with the hope it can be useful to others. The symptoms first experienced were a flickering image accompanied with muted clicking noises from the back of the monitor. This happened every so often, and it degraded to a complete dark display (no image) within one week.

With the help of information posted in this forum, it was determined that the power supply board was working correctly, providing stable 19 V and 7.3 V to the main board.

Now onto troubleshooting the main board…

I drafted a circuit that describes the power supplies implemented on the main board—see attached file. I started capturing a photo of the PCB and then drawing the tracks related to the (4) DC/DC Buck converters and the (2) voltage regulators. It's a bit unorthodox, as it is not a schematic nor a PCB diagram but a blend of the two. The circuit represents (partially) the BenQ manufactured board for the Dell UltraSharp 2405 FPW, which is marked as 48.L1E01.A02—a few notes about it:

• The dotted area you see on left is way to the left on the main board. It has been brought in for display purposes only.
• The +19V power rail (red wire) coming from the supply board feeds the IRF5305, IRF9024, and Si4431 MOSFETs, used for the 5.0V, 5.2V and 12V DC/DC Buck converters respectively. It also supplies power to the totem-pole transistors that drive each gate. I couldn't ascertain if the totem-pole transistor marked “t06” is PNP or NPN (Note 1).
• The +7.3V power rail (green wire) feeds the Si4431 MOSFET used for the 3.3V DC/DC Buck converter, which supplies power to the 2.5V (G950) and the 1.8V (G952) voltage regulators. It also supplies power to one of the TL1451A PWM controllers. Interestingly, Vcc for the other TL1451A is managed by the Genesis gm1601 display controller.
• All electrolytic cathodes are connected to ground, even if it's not drawn. All semiconductors shown with gray background are located on the front of the board, while the ones with no-background are located on the back of the board (this does not apply to resistors). The (6) S4 Schottky rectifier diodes are located on the back of the board.
• For the sake of simplicity, the voltage divider used for dead-time control (DTC) on each TL1451A PWM controller was not drawn on each control circuit (Note 2). Likewise, the 10K/10K voltage divider used for each error amplifier has been drawn only once, inside the TL1451A boxes—on the board there are two 10K/10K dividers connected from REF (pin 16) to IN- (pin 4 and pin 13) and onto ground, for each TL1451A.

In my case, I noticed the power rail to the T-Con (TP5) was low. It read 3.2 V, instead of the expected 5.0 V. It was caused by a 10K voltage divider resistor R14 on the back of the board that was open (~4 M).

[carbonosilicio]

Re: DELL 2405fpw

Hi!

What D19 zener diode value you used?

Thank you!

Got the order from digikey today. Replaced the failed big cap. Soldered on the new mosfet and got 5V back, so the zener diode and fuse went in as well.

Unfortunately, the yellow screen still persists. It doesn't seem to be a backlight issue (I'm seeing 18.7V to the inverter, and a nice bright bluish light from the ccfl). The tcon board is making a bit of a buzzing noise. Could that cause this? The left/right edges show a particularly darker yellowing, although the entire display is as if I had nightmode/f.lux on.

edit: forgot to mention I'm seeing stable 1.8v/2.5v/3.3v for the 3 fets on the tcon board

[dezsi001]

Re: DELL 2405fpw

Hello!
My 2405FPW monitor T-CON panel defect. The C97 capacitor short.
Anyone know what the value of the capacitor?
Thanks
Dezso

[ziddey]

Re: DELL 2405fpw

Sorry, I passed the edit period again. New main cap measures 160v when off, and 214v when on. I've seen reports of higher voltages in the 300 range. Is there a problem here?

When off, the power board emits a slight squeal if the logic board is attached. Goes away when turned on. Could be more caps that require replacing, but at this point, I'd like to solve the yellow picture before other repairs.

Tcon board only buzzes when the lcd ribbon is attached.

edit: Damn. Not sure what happened. Been using the monitor all day with the new FET and had no issues. Took it down to poke around a bit more. Set it back up, and a few minutes later, the new FET smoked itself and is shorting out. Good thing I soldered the new zener diode in. ?!?!?!?!?!

[ziddey]

Re: DELL 2405fpw

Got the order from digikey today. Replaced the failed big cap. Soldered on the new mosfet and got 5V back, so the zener diode and fuse went in as well.

Unfortunately, the yellow screen still persists. It doesn't seem to be a backlight issue (I'm seeing 18.7V to the inverter, and a nice bright bluish light from the ccfl). The tcon board is making a bit of a buzzing noise. Could that cause this? The left/right edges show a particularly darker yellowing, although the entire display is as if I had nightmode/f.lux on.

edit: forgot to mention I'm seeing stable 1.8v/2.5v/3.3v for the 3 fets on the tcon board

[ziddey]

Re: DELL 2405fpw

Here are some poor pictures showing the yellowing. There's a sliver of a dell 2005fpw to the right, which shows the proper color.

Despite the yellow tint, it's definitely not dimly lit. Am seeing stable 18.7V going to the backlight inverter..

[ziddey]

Re: DELL 2405fpw

I've been using the monitor, supplying 5V externally. However, it has a severe yellow tint all around, especially so on the left/right edges. Settings have been reset to no avail. Occurs on both DVI and DSUB. Something with the backlight/inverter?

[ziddey]

Re: DELL 2405fpw

I've also come across a dead 2405fpw.

F701, Q1, and D19 need replacement. As well, the main cap is oozing, squeals when off, and isn't able to provide a stable voltage (varies between 61v-64v).

D19 exploded and took out the solder pads. Looks like the unused R17 is a suitable spot to solder a replacement diode.

Before I realized what the situation was, I jumped the blown fuse with an ammeter for less than a second and saw 14A. This caused the buck inductor to smoke up and melt slightly. So that's probably worth replacing as well.

Will probably be placing an order with digikey, but I'm wondering why most people have opted to go the custom route instead of replacing these components? Is there something else I'm overlooking, and simply replacing F5305S, the diode, fuse, and inductor (if I've wrecked mine) won't fix?

Otherwise, could someone provide the part number for the blown D19 diode, the buck inductor, and the 5a fuse? The fuse is yellow and says 5A LF (littelfuse brand?)
As well, I see there's a few variations of the F5305S: http://www.digikey.com/product-searc...eywords=F5305S Any particular one I should get?

I have tested by supplying my own 5V directly to the fuse on the tcon board, and the monitor seems to work great. If there are more tests I can do to conclude that these are the only parts I need, I'm good to give it a go. Otherwise, I might just ghetto-rig something so that I can run it with my own 5V (perhaps pulling from my computer psu)

I've got Q1 (F5305S) removed, and D19 area cleaned up (R17 ready for the replacement diode)

As it is now, with an automotive 5A fuse soldered at F701, I'm seeing voltage at Q1.

Thanks everyone

[cheebster]

Re: DELL 2405fpw

Reviving an old thread here. Mine was a bit different, well the Q19 zener was shorted, no 5V, and q1 was blown. So i just removed the zener, q1 and 2 caps and injected 5VDC 5A as per https://www.cse.iitb.ac.in/~soumen/S...2405fpwRepair/

Nothing still. While poking around i found a bad fuse in the inverter area. So i shored it, and i blew a transistor, named 4512C in the inverter, it catched fire. it's at the q4 location.

I'm not going anywhere with that one, i can't see any display even with a flashlight of the please connect signal or anything. Upon connecting the power, the screen automatically powers on and the front panel buttons work. I see 22V and 7V at the power supply ! Any input would be great.

[Oblak]

Re: DELL 2405fpw

Hello,
I have 2405FPW with a broken PSU. Which equivalents do you recommend for a power mosfets, signal mosfets/BJTs and signal diodes?


Regards

[Uksa007]

Re: DELL 2405fpw

I have a similar issue to david, All voltages seem ok apart from the output of Q1 is 1.2v should be 5v?

Did anyone ever find out what causes this?

[DavidYon47]

Stupidity vs Cleverness, the fallout....

To recover some of my mental health and see at least something good come out of all this, I am offering the following:

• The first one to PM me can have the guts of the monitor for free. Power board, main board, driver board, USB board, CFL board. Take one, take 'em all. It has the daughterboard on there as a repair and seems to work here on my bench, even with a cracked screen.
• The second one to PM me gets an assembled and tested daughterboard, plus header pins for mounting. I'll also include a surface mount 6.8V zener for D19. Clearing the existing MOSFET/Caps/Coil is an exercise for the reader (hint: it's not as fun as it looks), as is replacing the zener (which is easier than it looks, esp if you have any SMD hand-soldering experience at all).

That's all I have left. The screen is a loss. The guts seem to work. I milled a spare daughterboard and bought an extra SMPS module which I likely will never use. May as well go someplace where it has a chance of being useful to somebody.

[DavidYon47]

Stupidity vs Cleverness: Stupidity wins the day every time...

So with the help of this thread, I've been homing in on the problem with my 2405fpw. I was only getting 1.2V on the drain of the MOSFET, so I went the route of replacing D19, ripping out the MOSFET, caps, and coil, and putting an SMPS module in its stead (same as others have done on this thread).

Having a fancy Othermill and a DIY reflow oven, I decided to get fancier than tack-soldering in the SMPS. So I designed and milled a board, and then promptly destroyed the SMPS module when I was pulling it out of the reflow oven when it got caught on the temp probe and fell to the bottom of the oven. In case anyone is wondering, a surface-mount module which itself is a surface-mount board will in fact reflow a second time when you reflow it to your main board. And if it hasn't cooled down before it drops 3", the parts will come flying off the module.

But that was only Stupid Part A. I ordered a replacement (two this time), and successfully reflowed it, tested, then installed onto the monitor's main board. And yes, I had 5V instead of 1.2V. And yes, the monitor came back to life!

Now, Stupid Part B. Given how long this took, and how big the monitor is, I kept having to set it aside to work on other tasks. At some point (unclear where), I set it down on a surface I thought was safe, but was not. Big long crack in the screen---now it's junk.

Clever Part A+B+C was to design and assemble my own daughterboard, which was designed to sit on male pins that replace the two caps for the output, and a bent pin to contact the Source pad on the MOSFET. Dimensionally I got the board 100% correct the first time---everything lines up perfectly (with some jiggering of the bent pin).

Attached are photos of the board, a dry-fit of the 1st SMPS that eventually plummeted to its demise, and a shot of the whole thing in context, including the pins. The trim resistor solders to the holes on the right side of the board, and a surface mount LED and current-limiting resister get reflowed to pads on the lower left.

[sentner]

Re: DELL 2405fpw

Update! I did some further checking, and found a webpage by a guy who offers a repair service for these monitors. He gave a couple of tips of what voltages to expect at various points, and that led me to find that the 19V rail fuse F701 had blown! So, I jumpered over it with a 5A glass fuse to test, and when I turned it on I got the test pattern!

I didn't have a 5A slow-blow through-hole fuse like was on there (and didn't want to wait for yet another digikey order) so I instead moved the 5A fuse from the 7V rail (F702) over there, and then replaced F702 with the glass one, using a fuse holder that I had sitting in my toolbox from an old project. I did it this way because F701 is hard to access, but F702 is in the open.

Are there any problems with leaving the glass fuse in there (250V 5A bussman slow-blow)?

[sentner]

Re: DELL 2405fpw

I am having a similar problem to those on this thread and wonder if someone can point me in the right direction.

It started with a high pitched noise that had lasted for a couple months. I decided to re-cap the power supply, but the very day the caps arrived in the mail, the monitor suddenly went blank. Backlight was still on, but the LCD display "drained" quickly (faded to black starting at top of screen and working down).

I found that D19 had overheated and lifted the trace off the board, and Q1 was shorted. I also checked R14 as Tduaong suggested and it was fine, but R9 right next to it was reading 50Mohms (though it was specified as a 10K resistor). I replaced that one as well.

However, I still have the same symptoms.. Can anyone point me as to what voltages I should get at various test points on the boards? It turns on, and I can switch inputs (indicator number on the front changes), and backlight comes on, but no picture..

[ucdzombie]

Re: DELL 2405fpw

Ahh my final post with pictures of the repair and a working monitor. I would like to thank everyone once again for their help!

Hello, can you show me how you connected the SMPS to the L1 connector? I'm a complete dummy. I tried to do the same repair but didn't work. So I want to try the SMPS trick.

[Tduong29@hotmail.com]

Re: DELL 2405fpw

Ok no good Installed MOSFET and D19 DIODE and left the T-CON disconnected... Took a voltage reading of the DRAIN and it was 0 again. Both gate and source where 18.8 where they were last time. So I guess the gate logic is bad?

Ok no good Installed MOSFET and D19 DIODE and left the T-CON disconnected... Took a voltage reading of the DRAIN and it was 0 again. Both gate and source where 18.8 where they were last time. So I guess the gate logic is bad?

Hello everyone!
Before I give the solution to this problem please allow me to introduce myself.
My name is Dan, I've join this forum for some short time now, however this is my first post. I wan't thank everyone that blogs to provide their expertise over the internet from just looking at some pictures (amazing) and reading some symptoms, also I want to thank everyone else for posting their problems (broken electronics) because without them, this site would not be possible. Im truly grateful for this forum. It has helped me numerous times when I'm lost.
So I am honored to be able to provide a solution to this problem today.

Here it is,
If your MOSFET shorted out, it most likely will take out your Z-Duode also. If that's the case, replace both. If your MOSFET is dead but open (my situation), your diode should be fine, just replace the MOSFET.

But you're not done yet. The reason that it still doesn't work is because the controller chip (U1 pin 13) on the main board is not getting its input voltage of 1.4v. The reason is because a 10K surface mount resistor (R14) on the back is also burned out leaving the circuit open.

1. Make sure the monitor is in the ON position and that you can see the back light is lit before proceeding.

2. Unplug the power cable from the monitor (while its still on).

3. Take the main board out, unplug everything except the connector from the power supply.

4. With the main board in your hands still hooked up to only the power supply, plug the power cable back to the monitor. It should come back on and the back light lit up.

5. Use an ohm meter to test the voltage from Ground to the resistor R14 on the back of the main board (just under the MOSFET at the corner of the board). One side should read about 2.5V the other side (goes to pin 13 of U1) should be about 1.4v. If you don't get the 1.4V, replace that 10k resistor and that should solve all your problem under $5.

[jaded788]

Re: DELL 2405fpw

what was your total cost for this repair? you can buy this board for roughly $50 if you can find it.

[budm]

Re: DELL 2405fpw

That's great, thank you for the follow-up and great job.

[Mirage00]

Re: DELL 2405fpw

Ahh my final post with pictures of the repair and a working monitor. I would like to thank everyone once again for their help!