Voltage Injection on 3.3v rail
I am repairing a laptop that has a short on it's 3.3v rail. I injected 1v on the rail and it was pulling 200mv but can't find any heat anywhere with thermal camera or alcohol. What else can I do to find what's shorted?
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go to 2v or 3v to get it to draw more current maybe.
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Went to 3v and still no heat source found.Comment
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When I turn it up it won't take any more because it's only 200ma the board is drawing. I can't force more amps in.Comment
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That's strange, but what is the resistance on this bus then, is it just a short circuit?
What kind of power supply do you have? Can it output 5-10A? If yours is rated for 1-3A, it's too weak for laptops.Last edited by lotas; Yesterday, 09:05 AM.Comment
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maybe the short is behind a mosfet that has not been turned on,
a secondary buck psu maybe.
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Maybe is some lab psu with short circuit protection kick in... what model of psu you have?Comment
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3.3v coil - 25 ohms
5v coil - OL
The other 3 coils on the board are showing
250 ohms
45.3 ohms
4000 mega ohms
I'm assuming the 3v is shorted maybe?
When I power the laptop on, it shows as dead. No CPU heat, no picture and no fan. However I noticed the 3.3v and 5v coils are showing the right voltages.
No 3.3v is showing on the BIOS chip pin 8
Voltages on the other 3 coils are showing 0vComment
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You have 3.3v and 5v on coil, but also 3.3v and 5v ldo from pmic. What is resistance of ldo 3.3v and 5v to ground? Oh, you are all over the forum... I see that laptom has common fault on usbc connector, have you check if voltage reach board without battery?Comment
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To be honest, I wouldn't know where to find the LDO. That's a new term for me.
I am aware this particular model has lots of problems with the USB-C connector. It's pulling only 5v through the USB-C charger but will check if it's reaching the board without battery and get back to you 👍🏻Comment
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Yes the 5v it's pulling from the charger is reaching the board, it's passing through a couple of MOSFETs and capacitor's.Comment
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As example of ldo in attach, it is useful to check what pmic you have and if it have ldo 3v3 on power button, sometimes with addition to 5v ok and they are working ok. Be systematic in repair, so do nor just repair on first sight. If is usbc data lines is broken, the pd controler not let charger to switch to 19v, nor enable batt charging... so, changeing pd controler before check continuity pin-to-pin endpin it may not solve the problem. Check on every mosfet if not shorted also, it is routine check like checking rails...Attached FilesComment
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Hi,
Try to repair a Thinkpad P72 EP720 NM-B723 MB with I7-8850H processor and N18E-Q1-KB-A1 (P3200) GPU with 6GB memory. Unfortunately there is noinfo what happened to the laptop. I got it disassembled with parts missing, like keyboard, battery.
Unfortunately I have no schematic available for me (requested in the sub porum) but got the boardview file.
Symptom: after connecting to the charger the power led light up for one-two second and switch off. After a couple secons the power led light up for half a second and switch off. No battery, no IO board, no... -
Hello everyone,
I recently picked up a laptop that was about to be thrown away to try to repair it. I've tested quite a few things, but I don't know where to look anymore. Could you please help me?
Brand: Asus Vivobook
Motherboard reference: x421da, Rev 2
Context:
The person who gave it to me mentioned it might have been exposed to water, but they weren't sure. After opening it up, I couldn't find any signs of water damage or oxidation on the motherboard.
The first thing I did was to connect the PC to a power supply: 19V stable and... -
Hello, I recently use PSU for voltage injection. I sent 1.2v 5A in big MSI motherboard and I felt nothing geting warm with my fingers (don't have termal camera). Finally chipset is dead (saw by using meter).
So voltage injection don't work, but it's big gamer laptop MB so, why not. But I used voltage injection again for small Asus Zenbook lapotp (14'). 1.5v 5A and I felt nothing again. Probably CPU/chipset dead because caps at reverse side are shorted to ground (0 Ohms) but I felt no warm. I used thermal probe and temps grew up for 4 degree C. Low for 7.5W ?
What's... -
Hi everyone,
I have a strange problem (for me) on an MSI GT70 2PE laptop.
When it's under heavy load, power goes steadily to the battery (for 2 or 3 seconds) then return to the charger. If I remove the battery it turns off.
The higher the load, the lower the voltage on the main rail. We go from 19.5V, PC connected to the charger but turned off (normal consumption of 0.06A)
On, when it draws 2A the voltage is 19.2V, then eventually collapses to 18.5V (and turns off) around 5A.
I removed the first 2 mosfets (PQ13 & 14) from the main rail, without noticeable change.... -
Hi,
I'm learning electronics(already have some basics) by fixing a FH52M LA-J891P rev1B. It come from an acer nitro 5. The charger was defaulting upon pluging. The 19V rail resistance is 0ohm (I believe that caps screw my measurement). When i inject 5A, I get a rail tension of 1.3V, and 0.8V vcccore.
Except the cpu, I cant feel anything getting warmer.
I believe that it is normal, because the cpu is "eating" half the power I'm imputing.
I dont know if the cpu is fried, because I did not remove the big capacitor on vcccore.
I believe that if the cpu was fried,...
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