Trying to revive an HP laptop - Page 1
Forum section: electronics / beginners

author: Jupitus
author_rank: Contributor
timestamp: December 31, 2023, 02:45:40 pm
content: Hi Everyone!I am hoping some of the wise owls here might be able to offer me a few bits of advice or insight.I am in possession of my son's rather old HP laptop, model number 15-bs506na >https://support.hp.com/gb-en/document/c05864977He does now have a replacement, so this is an attempt to recover the laptop for my own education, practice and then to repurpose it on other areas hence it is not critical and has no data recovery requirement associated. Basically, it expired on him - no LEDs when connected to the DC supply, and nothing apparently happening when attempting to power it on.On external advice, I have replaced the DC in port on the laptop and subsequently tried a replacement power supply (tested with multimeter and showing 19V or so) and also a replacement battery. No apparent change.At this point, we got him a replacement laptop so I could then completely destroy this with my amateur repair abilitiesI have the motherboard out of the device which is marked CSL50/CSL52 LA-E811P and I hope have done a fair amount of research myself to justify now asking what hopefully will not be embarrassingly silly questions.Hours of searching, and the closest I seem to be able to find to a schematic for the board is that of an LA-D707P model, although I have read they are supposedly quite similar. I then set about looking for shorted components as that seems to be a thing I see seemingly knowledgeable YouTubers do. I believe I have tested all capacitors on the board and I did find one capacitor which is shorted to ground (underlined yellow in my image). This is adjacent to a 20 pin IC which I have managed to identify as an RT6575DGQW Realtek DC step down component hence linked to the power rails on the board. This is where I hit a roadblock. I am tempted to simply see what happens if I replace the capacitor, but I am struggling to work out what value capacitor I should replace it with using the board schematic I have and the realtek data sheets.The datasheet lists pin3 (ie the one connected to the failed capacitor) as 3.3V output, but I can't locate the equivalent IC in the board schematic I am using to see what capacitor would be correct. In addition, am I barking up the right tree, or should I be trying to work out why the capacitor failed first?I hope I have included the main relevant details, but do please let me know if I have missed information out. Thanks in advance, folks!!

author: Jwillis
author_rank: Super Contributor
timestamp: December 31, 2023, 06:24:38 pm
content: A lot of the time you get away with consulting the Data sheet athttps://www.digikey.ca/en/products/detail/richtek-usa-inc/rt6575bgqw/16376704.Sorry I can't seem to get the UK Digikey for some odd reason.It shows a different package but the pin outs should be the same.Having a hard time seeing if it's a WQFN-20 or if those are pins.Page 10 shows a typical application circuit and shows that capacitor as 1uF.Was the cap destroyed or intact?

author: Jupitus
author_rank: Contributor
timestamp: December 31, 2023, 07:19:49 pm
content: Thanks for your replyIt has pins... as per picture... the cap is still intact and I can't see cracks or anything, although I don't possess a microscope, sadly.

author: Jupitus
author_rank: Contributor
timestamp: December 31, 2023, 07:23:08 pm
content: Oh, I also discovered that on the schematic I have for a similar laptop, they do include this:https://www.richtek.com/assets/product_file/RT8243A=RT8243B=RT8243C/DS8243ABC-07.pdfwhich has a lot of similarities to the chip I can see near the cap:https://www.richtek.com/assets/product_file/RT6575C=RT6575D/DS6575CD-04.pdfEDIT: The similar datasheet suggests a 4.7 uF cap, 10V ?

author: p.larner
author_rank: Frequent Contributor
timestamp: December 31, 2023, 07:39:40 pm
content: can you not tack an electrolytec either side of it (PIGGYBACK) and see if it powers up?.

author: Jupitus
author_rank: Contributor
timestamp: December 31, 2023, 08:55:20 pm
content: If the bad cap is shorted to ground, won't the current just go to ground???

author: Jwillis
author_rank: Super Contributor
timestamp: December 31, 2023, 09:27:26 pm
content: If it's shorted it will have to be removed anyway. A 6V 1uF would be small enough to tack in there as p.larner suggested.

author: Jupitus
author_rank: Contributor
timestamp: December 31, 2023, 09:50:30 pm
content: Ahhh yes, that does make sense. In short, get rid of blown cap, and use a simple replacement just to test if it improves the issue. If it does, then I am on the right lines and can source what I believe is the correct part and fit that. Nice! Thanks folks !!

author: Infraviolet
author_rank: Super Contributor
timestamp: January 03, 2024, 12:22:44 am
content: If you think all the trouble with the laptop relates to its internal generation of DC voltages below the power supply voltage, your best option might be to work out what each voltage should be, then supply these manually from (initially) external voltage sources. See if the laptop can operate (you might have to connect all peripheral cables to get it as far as showing BIOS/UEFI, I have found some laptops just turn straight off if you try to power on the main board when disassembled without the screen connector and others attached), then you'll know the flaw has been a lack of these supplied voltages. You'll probably want to isolate the chips which supply the voltage in to these rails, maybe there's somewhere between the voltage converter chips and the stuf actually usaing those voltages at which top or bottom layer traces could be cut, repariing with a solder bridge later once the testing is done. Many types of DC converter don't behave well if they have a voltage supplied at their output when they aren't being supplied from their inputs (I've seen small sparks from it once, for a 5V buck regulator).