Dell Latitude 5520 motherboard repair - Page 1
Forum section: electronics / repair

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 26, 2025, 12:34:30 pm
content: Hey all, I have been working on a laptop for a family friend for a while now, mostly waiting on parts to ship. I have replaced all the things I have suspected. It started off no power at all the 2 USB C ports one took 0 power the other would turn on my meter but only 5v 0a. I replaced the PD controller and then the battery would charge at 20v on both ports but a voltage regulator chip was getting hot so I replaced that and now I get keyboard backlight and power button light and it loops like that. I occasionally get 2 or 3 orange and then 3 white blinks. I have swapped ram to see if that was the issue as that is what I read could be those lights but same thing. I found one of the power rails I believe VDDQ is 0v which I had been looking into if that is my problem but I have petered out on progress. I also read that the 3 orange and 3 white can be a corrupt bios, should I look into this> I can pull the chip and dump the bios and try and install new bios if need be but I don't know if it is worth wasting my time if that isn't the problem. Also the caps lock light doesn't always turn on with the keyboard backlight but I am unsure if that is relevant. any advice on what to look into next would be very appreciated.

author: touchatout
author_rank: Contributor
timestamp: March 26, 2025, 06:12:44 pm
content: Hello,Hard to tell what could be wrong as you attempted quite a lot of things and I don't know how much you are skilled at soldering and if the work was done properly.I once experienced a extremely strange quite similar behavior with a HP EliteBook x360 1030 G3, after replacing one of its USB ports.The computer had very strange symptoms : not booting, not charging, and maybe also not turning on at all.It also had some weird diode behaviour, not necessarily identical, but quite similar to the one you are facing.Of course, I had tried all possible things to reset the charging firmware, like unplugging the power supply, removing the battery and holding the power button down for 15 seconds or more, before plugging the power supply again.Nothing was working and I really could not figure out what I had done wrong. I finally had to buy an identical laptop for the client.I forgot this computer about one year and tested it again.The battery had be drained by the long waiting but was still in good condition.It accepted to charge andthe laptop came back to life, perfectly working without that I had anything to do !Conclusion:Some laptop battery firmwares may be badly designed to face some unexpected situations like battery removal.It is also possible that some battery BMS are badly designed. A drained battery can sometimes bring the situation back to the normal.Here are things I would recommend:Document yourself about the procedure to reset battery settings for your laptop model and attempt it.For most brands, it is holding the power button down during 15 seconds or more, with no power source (i.e. no power supply and no battery)Make sure the battery is in good condition. (Did you test if the battery was charging before doing the repair ?)Helping you from a small spike, and watching under the stereomicroscope, make sure that the USB-C ports are properly soldered and that there are no invisible cracks where the pins meet the board. Since their pitch is around 1mm only, desoldered USB-C ports may cause unpredictible failures due to wrong pins touching the tracks.Make sure you are using a power supply that delivery the right voltage and enough current.If you can, discharge the battery artificially, for instance using a laptop of the same model.Make sure that there is no small piece of towel paper in your keyboard (typically after cleaning it).Look at the troubleshooting official documentation for your laptop model as it may help to diagnose the problem from the diode behaviour.Ask the Dell community.Forget the laptop for about six months or one year and try again.Hope this helps.

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 27, 2025, 11:28:50 am
content: Thanks for the suggestion, I have also removed and swapped the USB c ports as one of the first things I did, they should be on well but I suppose anything is possible. just yestarday I was getting 3 amber and 3 white lights so in my research I read it could be a corrupted bios or failed CPU I tried reprogramming the EEPROM with a "Good" Bios with not much change.

author: watchmaker
author_rank: Unknown
timestamp: March 28, 2025, 04:32:15 pm
content: I just looked on ebay. Have you considered just buying replacement MB? From a seller who provides a30 day return of course.For the effort you put in it may be worth it. here is one example:https://www.ebay.com/itm/296984821430?

author: u666sa
author_rank: Frequent Contributor
timestamp: March 29, 2025, 12:16:56 pm
content: Quote from: CoopedUp on March 26, 2025, 12:34:30 pmYou gotta look around your EC chip. Either replace it, or flash new EC BIOS into it. If you do decide to replace it, don't forget that it's programmable. Frankly, if it's Intel mobo you got BIOS, you got EC BIOS and you got ME BIOS to worry about.To me it sounds like an EC chip -- provided you used thermal camera to make sure other stuff is not getting hot.Before you dive this deep, check resistance on CPU and GPU coils. You don't want to be dumping money into it only to later find out it's dead CPU or GPU.

author: u666sa
author_rank: Frequent Contributor
timestamp: March 29, 2025, 12:32:48 pm
content: Quote from: watchmaker on March 28, 2025, 04:32:15 pm

author: watchmaker
author_rank: Unknown
timestamp: March 29, 2025, 01:17:57 pm
content: I just picked one at random from those offering returns. Here is another that may meet your approval. The point is to look at replacing the entire subassembly rather than following rabbits.I did not think it was my job to SELECT the replacement given I have no idea which model he has.https://www.ebay.com/itm/364117903760?

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 30, 2025, 02:19:01 pm
content: I appreciate all of the replies on this. I agree that it would be easier to just replace all of the parts with a mobo swap. that being said I re replaced the vrm or whatever it is called. it then seemed to stabilize the fault code now no longer "boot" looping it just repeats a fault code of 3 amber 5 white signalling issue with ram. I know I am not getting the 2.5v rail though which I think would also show as that code seeing as the ram needs the 2.5 rail. the IC for 2d5v is not getting its enable signal and that does come from the CPU. I checked for shorts and the CPU seems fine in all the ways I have checked. I have a thermal cam and monitored temps on attempt of boot it gets slightly warm. The 1v VCORE is also not 1v it has the pwm1 and pwm2 as well as I think fccm to the switching regs but they are not outputting. I have been trying to follow the boot up power diagram but I am having a hard time figuring out the exact order. I am leaning towards the CPU side is not gretting the apropriate power so it cant tell the other power rails to turn on and then the ram would get 2d5v. I will continue my search for answers but that is where I am at. I also put the old bios back on it as I wasnt sure if there is any firmware locks for serialization or something like that.

author: touchatout
author_rank: Contributor
timestamp: March 30, 2025, 03:21:51 pm
content: I cannot tell about diodes for this specific model, but consider that, booting issues with weird diode signals often come from keyboards that either badly connected or damaged, especially for those connected with a flex ribbon cable like the one that the Dell Latitude 5520 uses.Disconnect the keyboard cable on both sides(keyboard & mainboard).Reconnect it againpaying special attention that it is properly aligned and clipped. If necessary, increase its thickness with thin adhesive tape like polyimide film. Try again.If it does not suffice,detach all unnecessary components, like speakers, wlan card (wifi), other PCBs if any, a.s.o., and try again.With a voltmeter, check that the voltage of theBIOS/CMOS/RTC button cell battery is between 3V and 3.3V. If below 2.6V, replace it.Try again.If it does not suffice,remove all RAM sticks. Maybe some alarm will come when you power the laptop on. This is normal.If you did a RAM upgrade,make sure that the RAM stick you insert is compatible with the laptop. For some laptops, it does not suffice that it is DDR3.I like using those with 8 RAM chips per side as they tend to be more compatible than those with only 4 chips per side. (e.g. for MacBooks)Lastly, consider that the keyboard ribbon cable may have been elongated when you opened the laptop case. On modern keyboard ribbons, tracks are done of tiny printed conductive adjacent randomly distributed droplets in order to use as little material as possible. If they do not touch themselved enough, one or many keyboard tracks are broken, which can lead to weird issues.Hope that one of those tricks will help.

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 31, 2025, 10:40:09 am
content: I have been troubleshooting this with the keyboard and trackpad disconnected. My latest discovery is that the enable signal for the 2d5v rail is infact on it is 3.3v and the regulator is not outputting anything. I ordered some replacements and I hope that fixes my issue. I was beginning to worry the cpu or SIO chip were bad but I think that may not be the case. still wont rule that out but I have more hope.

author: touchatout
author_rank: Contributor
timestamp: March 31, 2025, 12:42:56 pm
content: And the voltage of the CMOS battery is okay?It is always one of the first things that I check. If lower than 2.7V you should care.Whether you are above or under this threshold makes major difference in the way the computer behaves.It its kind of "1" and "0". (High level / Low level).Search for "CMOS voltage threshold" for more info.

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 31, 2025, 01:39:05 pm
content: I will have to check that cmos voltage but I have been troubleshooting this with it on and off and it doesn't change anything. Could be an issue as I didn't think about that. I have ordered the replacement 2.5v reg so I'm really crossing my fingers that is the last issue. It sure what kind of event would have killed the PD controller, 2.5v reg and what I believe is called the VRM multi phase power controller. The computer recognizes that the ram in not there as the power supply for the ram is not on so maybe just maybe it will work

author: CoopedUp
author_rank: Regular Contributor
timestamp: April 07, 2025, 11:06:08 pm
content: Well I got the 2d5v reg and installed it. I now have all of the power rails except for Vcore. The led indicator turns on white with the keyboard and then turns off after a few seconds. Nothing is really getting hot but the smaller rectangle on the CPU gets slightly warm looking through the thermal camera. The cmos voltage is 3.05 volts. I have tried different ram in different spots also. Yet another part changed and another step with different symptoms lol