Mosfet problem  - Page 1
Forum section: electronics / beginners

author: falen555
author_rank: Newbie
timestamp: July 15, 2023, 02:57:35 am
content: Hello from Ireland - new user here - first postIve been trying to fix a HP ProBook 470 G1 Laptop for some time.It has an random habit of just turning off - no warning , just bang - dead. Usually fixed by removing all power ( battery , cmos ) and it comes back on. ( its a common problem with HP laptops , the white flashing led on the power jack )From watching allot of videos many say it is one of the mosfetsso following tutorials i started trying to find the bad chipI was following the 19v from the power jack in , reading the voltages with the meterthen one of the meter probes moved and shorted out 2 tiny capacitors - i even sharpened the meter probes before i started , as the components are so tinynow it is totally dead - no flashing white light - nada !!!im hoping there is a fuse on the boardive looked at images of what smt fuses look like but cant find anythingI imaging the fuse has to be close to the power coming in - there is also the battery connector ( in the same local area ) but i cant see one there eitherthe smt components are so small i need a magnafying glass just to see them !!!i guess its possible ive fried the thing !!!I have good experience with soldering ( been recapping / restoring old 68K macs for years )cant read schematicsdont have an oscilloscope - just a multi meterand to top it off .......... zero electronics training.Nothing worse than trying to fix something , then only make it worsethanks folks

author: falen555
author_rank: Newbie
timestamp: July 15, 2023, 03:20:28 am
content: Here is the board in question.The lead on the left is the from battery , the lead on the right is from the power supply.Where is the fuse !!!!!!

author: ArdWar
author_rank: Frequent Contributor
timestamp: July 15, 2023, 03:43:12 am
content: It might use eFuse instead. Can't exactly discern what topology the two SO8 MOSFETs near the 19v inputs are in. I spy a RT9724 in the low voltage power path, the main 19v power path controller is probably in the other side.

author: falen555
author_rank: Newbie
timestamp: July 15, 2023, 03:46:13 am
content: doing some more reading I read that they dont really use fuses anymore !!!This laptop is about 10 years old - im trying to get it going again as it is a 17 inch displaythis is just a dumb idea but if it already has a dodgy mosfet , would me shorting the 19v finish off the mosfetits looking more like a one way trip to the bin for this old machine

author: falen555
author_rank: Newbie
timestamp: July 15, 2023, 03:54:14 am
content: Hi ArdWarJust took a pic of the other sideI have no idea about modern electronics - Im used to working on 30 year old macs ..... allot more forgivingBenn watching vids all day of people metering out the board - i was so careful and then bang , probe movedHow do people meter out these tiny components !!!!

author: ArdWar
author_rank: Frequent Contributor
timestamp: July 15, 2023, 03:55:20 am
content: 1124 is 1.1A 24V fuse, tho I doubt it was the (only) one problematic.Without any familiarity with its particular failure modes you can try isolating each subsection and testing for expected response to external stimulus. But that require you to reverse engineer or at least guessing the circuit topology first.Not worth unless you happens to have access to particular schematic and/or boardview

author: falen555
author_rank: Newbie
timestamp: July 15, 2023, 04:21:57 am
content: as in P1124 ?all i can do is put the meter on it and see if its blownother than that i turned a small problem into a fatality !!!Thanks for all your help ArdWar

author: Faranight
author_rank: Unknown
timestamp: July 15, 2023, 07:13:57 am
content: I recommend you go to Youtube and search for a channel by the name NorthridgeFix.Watch some of the repair videos and you're going to learn a lot about fixing dead motherboards.