Dell 2405FPW PSU - Page 1
Forum section: electronics / repair

author: Cloud
author_rank: Regular Contributor
timestamp: October 16, 2015, 11:56:45 am
content: Today I salvaged a Dell 2405FPW, because I thought that it probably just has a few bad caps. But the problem is bigger than this. The transistor, IC651 & IC601 on PSU went bad. Does anyone know markings of these elements or maybe has a picture of a bottom side of a PCB? I would be very grateful

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: October 16, 2015, 12:52:44 pm
content: I will try and get you some photos. Mine went bad a week or two ago and has been sitting disassembled.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: October 16, 2015, 01:43:59 pm
content: IC601 is labeled 200A6 PCGW (ON Semiconductor?)IC605 is L6561D Z518 (ST Microelectronics)Attached is a photo of the bottom of my board.

author: Cloud
author_rank: Regular Contributor
timestamp: October 16, 2015, 07:13:59 pm
content: Thank you very much. I think that from that I will be able to repair it. I am just hoping that the PSU is the only problem

author: Cloud
author_rank: Regular Contributor
timestamp: October 16, 2015, 08:58:56 pm
content: If it wouldn't be too much trouble could you please check the following elements with diode tester and tell me if on your board also appear faulty (so I can know if its faulty element or if its because of surrounding elements)D604R614R623ZD601D603D655Q653Q651Q652Thank you

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 16, 2015, 09:03:41 pm
content: Is it just me, or is R615 (top left, under the two caps) burnt?(or is it just a black smudge)

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: October 16, 2015, 09:16:55 pm
content: Definitely looks burnt.Working late tonight and part of tomorrow. I will check it when I get back home on Saturday.Don't forget my monitor is also dead and I haven't had a chance to compare to my good one. I will have to do both so I can decide if it is worth fixing and let you know what I measure on the good ps.

author: Cloud
author_rank: Regular Contributor
timestamp: October 17, 2015, 02:19:16 pm
content: @crispy_tofu it looks burnt, but I don't have proper equipment to check if it is still 0.22Ohm or not, so just to be sure I've replaced it.@ManateeMafia today I was talking with a friend who is repairing monitors and he said that probably most of the control circuit is dead and to be sure that each component is ok, the best way is to unsolder at least one end and measure it. Now I know what I will be doing new few days...

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: October 17, 2015, 02:36:57 pm
content: No problem for me, I am in the same boat. Yes, no good way other than test all suspected parts one by one.Most likely I will get it to the right board and order a replacement from a seller, unless I find bad caps on the ps.

author: Rasz
author_rank: Super Contributor
timestamp: October 19, 2015, 03:46:18 am
content: so many burned components and carbon buildup = i would just buy another supplyscambay has at least onehttp://www.ebay.com/itm/Dell-2405fpw-power-supply-/271958611917?hash=item3f51ff17cd:g:BBAAAOSwrklU2BI-

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 19, 2015, 04:00:03 am
content: Quote from: Rasz on October 19, 2015, 03:46:18 amUSD$40 in shipping to Slovenia (which is where OP lives)!! That's more expensive than the item itselfBut it might still be a cheap way to fix the PSU...

author: Rasz
author_rank: Super Contributor
timestamp: October 19, 2015, 04:04:07 am
content: Im sure Slovenia has some local ebay competitor, My point is might be cheaper and less stress to just look for broken monitor/whole board. This one looks like its going to be a trip full of surprises (maybe all mosfets, maybe even transformer, or controller chip).Another option is investigating what voltages you need and bodging in supply from another monitor

author: Cloud
author_rank: Regular Contributor
timestamp: November 30, 2015, 06:37:36 pm
content: Hello,Buying a new PSU isn't option. So I replaced both controller ICs, mosfets and capacitor. But on the output for the logic board I get a sine wave with frequency 50Hz. Tomorrow I will try to probe around gates of mosfets and transformers.

author: twice11
author_rank: Contributor
timestamp: November 30, 2015, 09:25:46 pm
content: These supplies are awful. I fixed one myself.The failure mode is that the primary cap goes bad (leaking electrolyte etches one of the connections away). The supply has PFC, which is a step-up converter outputting 400V into that cap. If the capacitor is suddenly disconnected from the circuit, the PFC coil discharges into, well, there is nothing to discharge into, so it kills the primary switching mosfet. The MOSFET fails by shorting all terminals, thus shorting the primary side. The 0.22Ohm resistor is afusibleresistor (which doubles as low-side current shunt), which blows and opens the circuit to, err, not really prevent any damage. As soon as the 0.22Ohm resistor is blown, the gate of the FET is connected to the unloaded full-wave rectified mains input. The PFC controller IC (an LT6561) is not very fond of getting fed +300V on its gate driver and blows, too.Further collateral damage usually is created by shorts inside the PFC controller IC that apply high voltage to some SMD resistors and transistors (In my case, a 1k 0805 resistor and a SMD PNP transistor, which has been replaced by an MMBT3906). It is said on forums that sometimes a zener diode fails, too. A lot about fixing these supplies (also used in th Dell 2407, and if there is a 2406, in that one most likely, too) can be found in different forums, for example the badcaps forum.After swapping these parts and applying power, nothing happened, because the input fuse was blown too. Fixing the fuse made the primary bridge rectifier go boom (likely it already had one diode shorted). After swapping that one too, the supply worked again.The desing of that supply is quite interesting: Because of European Union regulations, devices consuming more than 75W need to have a good power factor which can be obtained by big chokes or active PFC, on the other hand, a PFC circuit increases quiescent current and thus may greatly reduce standby effectivity. This supply bypasses PFC in standby, and enables it in usual operation. As there is a diode (check that one, too...) from the bridge recitifier output to the main filter cap that conducts if the spontaneous rectified mains voltage exceeds the cap voltage, the PFC can be bypassed by just disabling the PFC controller chip. If I remember correctly, that's what the blown transistor was for.I think the output of the supply is 19V only, so replacing it with a cheap laptop supply might be an option. There are hacks on the internet about modifying the supply to allow external power input on the speaker bar supply jack.

author: Cloud
author_rank: Regular Contributor
timestamp: December 01, 2015, 08:45:35 am
content: Do you remeber which transistors had to be replaced?

author: tooki
author_rank: Super Contributor
timestamp: December 02, 2015, 10:58:19 am
content: If you guys need info/measurements from a working 2405FPW, let me know. I just upgraded to a new 27" display, so I'm willing to open my 2405FPW up for non-destructive testing.

author: Cloud
author_rank: Regular Contributor
timestamp: December 02, 2015, 01:48:03 pm
content: If you would be so kind. The voltages on the power connector to the logic board and to inverter. And if its possible a good quality picture of a bottom of a power board. So I could check out myself values of resistors that must be replaced

author: tooki
author_rank: Super Contributor
timestamp: December 02, 2015, 09:06:23 pm
content: OK, so here are the voltages. The pins are as countedon the destination board, since it's much easier to probe there.Inverter boardpowered on:3.23V1.45V18.9V18.9V18.9VGroundGroundInverter boardpowered off:.009V2.15V21.48V21.48V21.48VGroundGroundLogic boardpowered on:Ground0VGround7.32V3.23VGround18.9V1.46V3.24V0VLogic boardpowered off:Ground0VGround6.66V0VGround21.48V2.14V.009V0VPins 2 and 10 of the logic board donothave continuity to ground.As for the photo of the resistors, lucky for you, I have a CCD-based flatbed scanner (CCD means it has lots of depth of field) so I can scan things that aren't totally flat.Super gigantic 51 megapixel image (5.6MB)Quarter-size "small" versionYes, the big one really does make reading the SMD markings easier! It's of the whole board, in case you discover any more failed components you need the values of.

author: Cloud
author_rank: Regular Contributor
timestamp: December 03, 2015, 04:31:12 pm
content: Thank you very muchI'll try to just power on the logic board from lab supply to see, if it works. Because if it doesn't everything will go directly to trash.

author: tooki
author_rank: Super Contributor
timestamp: December 03, 2015, 05:55:41 pm
content: If it's dead, at least harvest the LCD panel - lots of useful light diffusion films in there!!

author: Cloud
author_rank: Regular Contributor
timestamp: December 20, 2015, 03:39:30 pm
content: On this lovely sunday morning, I had some spare time, so I started poking and probing this PSU.On the gate of first (stand by) mosfet I get spikes of cca 150mV and frequency 100Hz and on the second (working) I get 50mV.Voltage on the main capacitor is around 355V with ripples cca 0.8Vpp.Does anyone have an idea what should I check/replace?

author: Cloud
author_rank: Regular Contributor
timestamp: January 11, 2016, 10:47:11 pm
content: Today I was probing around PFC and have notices, that I don't even get +12V thereSo I tried to connect 12V to my lab supply and when I have pluged monitor to 230V, my lab supply was just showing 120mA. And on the output to mosfet still wasn't anything. I am starting to get desperate

author: Cloud
author_rank: Regular Contributor
timestamp: March 05, 2016, 10:28:50 pm
content: I managed to "convince" monitor to turn on the status lights and to react to those. I am figuring out, that the voltage regulator on the logic board if bad. Tomorrow I will try to figure that out and will probably replace it.Oh and I give up about repairing PSU. I will probably build my own PSU if I manage to get the monitor working

author: tooki
author_rank: Super Contributor
timestamp: March 06, 2016, 09:47:57 am
content: Keep me posted, I'm curious what you figure out.

author: Cloud
author_rank: Regular Contributor
timestamp: March 07, 2016, 11:25:58 pm
content: It looks like one of the mosfets on inverter board is bad. I am looking for a push-pull mosfet in SO8 housing.

author: Cloud
author_rank: Regular Contributor
timestamp: March 08, 2016, 10:28:02 pm
content: I have unsoldered all three mosfets, that were in short circuit and found out, that mosfets are actually okayThe problem is the high voltage driver OZ964. It has 25ohm resistance from pin 11 to the ground. I have ordered them from aliexpress, but I have a bad feeling about them. So I am looking for it somewhere in europe.

author: bubba198
author_rank: Contributor
timestamp: April 21, 2021, 03:52:26 pm
content: So did you ever get it to work? If yes what was the cause? Thank you!

author: libralect
author_rank: Contributor
timestamp: October 04, 2022, 09:54:49 am
content: Do you think I can bypass a failed PSU using a 19V PSU from a laptop? Perhaps the control board takes a 5V?That was the first 24" consumer LCD, from 2005. Oddly, it's better than a highly rated HP LCD bought in 2018. The PSU failed here too after only 12 years though, compared to our Hitachi TV which lasted 35 years. I would prefer to tape a laptop 19V and maybe cut some traces to the 5V pins if that's feasible! please advise!

author: Rasz
author_rank: Super Contributor
timestamp: October 04, 2022, 11:54:48 am
content: https://www.eevblog.com/forum/repair/dell-2405fpw-psu/msg812579/#msg812579has list of voltages, you will need separate 3.3V, not to mention the question of what will monitor do without standby voltage at all?its usually just caps dead in those supplies, why not replace them?