Hi everyone,
This is my first post so I'm hoping to get some help on this awesome forum. As a preface, I'm an amateur at electronics, especially troubleshooting complicated devices like laptops. However, I'm trying to develop a skill for it so I can learn how these devices work and how to repair them without continuing the wasteful tradition of throwing them away and buying new. 🤮
I've had a Lenovo Ideapad 5 14ITL05 for a few years now, with motherboard LA-K321P. I would never leave it plugged in unless I was using it, and always turned it off after I was done, but last week the laptop just wouldn't start upon plugging it in. I tried following a previous post on here, but due to my lack of knowledge in the subject, I am lost as where to look next.
I began by removing the back cover and exposing the internal components. I wanted to see if my PQB1, PQB2, and PQB13 MOSFETs were working properly, as suggested in the aforementioned post, as they handle providing voltage to the board from the USB bus. I recorded the following resistances between the sources, drains, and gates for each component:
PQB1
Source to Drain: 112.3 kΩ​ (5 -> 2)
Source to Gate2: 118.3kΩ (5 -> 8)
Source to Gate1: 8.04 MΩ (5 -> 1)
Drain to Gate1: 1.3 MΩ (3 -> 1)
Drain to Gate2: 1.6 MΩ (3 -> 8)
PQB2
Source to Drain: 2.85 kΩ (5 -> 2)
Source to Gate2: 115.4 kΩ (5 -> 8)
Source to Gate1: 74 kΩ (5 -> 1)
Drain to Gate1: 7.2 MΩ (3 -> 1)
Drain to Gate2: 219 kΩ (3 -> 8)
PQB13
Source to Drain: 300 kΩ
Source to Gate: 190 kΩ
Gate to Drain: 7.2 MΩ
However, I had two concerns while doing this:
1. How are the pins laid out for these components? I assumed that, starting from Pin 1, they would increment upwards counterclockwise. Meaning they would go 1, 2, 3, 4 descending on the left side, then 5, 6, 7, 8 ascending on the right side. Is this correct? I wasn't able to find a layout for these two MOSFETs (3635? GA1R3? for PQB1 and 36354 A1T24 for PQB2)
2. Are the pins in the below pictures properly soldered? To my eye, it looks as if one pin on each component isn't connected to the board, as the solder seems to bubble up on the tip.
3. My resistances kept fluctuating while measuring them. For example, the Source to Drain for PQB1 varied from as little as 70 kΩ to as large as 8 MΩ. Could this be due to my leads? They're the regular AMES leads-- rather large for SMD pins. I just ordered needle-point leads, so maybe should I try measuring these resistances again? I made sure the power was off for the entire process, and the battery is disconnected, so am I doing something wrong in how I am measuring it?
Thank you for your time!
tantr13 <3
This is my first post so I'm hoping to get some help on this awesome forum. As a preface, I'm an amateur at electronics, especially troubleshooting complicated devices like laptops. However, I'm trying to develop a skill for it so I can learn how these devices work and how to repair them without continuing the wasteful tradition of throwing them away and buying new. 🤮
I've had a Lenovo Ideapad 5 14ITL05 for a few years now, with motherboard LA-K321P. I would never leave it plugged in unless I was using it, and always turned it off after I was done, but last week the laptop just wouldn't start upon plugging it in. I tried following a previous post on here, but due to my lack of knowledge in the subject, I am lost as where to look next.
I began by removing the back cover and exposing the internal components. I wanted to see if my PQB1, PQB2, and PQB13 MOSFETs were working properly, as suggested in the aforementioned post, as they handle providing voltage to the board from the USB bus. I recorded the following resistances between the sources, drains, and gates for each component:
PQB1
Source to Drain: 112.3 kΩ​ (5 -> 2)
Source to Gate2: 118.3kΩ (5 -> 8)
Source to Gate1: 8.04 MΩ (5 -> 1)
Drain to Gate1: 1.3 MΩ (3 -> 1)
Drain to Gate2: 1.6 MΩ (3 -> 8)
PQB2
Source to Drain: 2.85 kΩ (5 -> 2)
Source to Gate2: 115.4 kΩ (5 -> 8)
Source to Gate1: 74 kΩ (5 -> 1)
Drain to Gate1: 7.2 MΩ (3 -> 1)
Drain to Gate2: 219 kΩ (3 -> 8)
PQB13
Source to Drain: 300 kΩ
Source to Gate: 190 kΩ
Gate to Drain: 7.2 MΩ
However, I had two concerns while doing this:
1. How are the pins laid out for these components? I assumed that, starting from Pin 1, they would increment upwards counterclockwise. Meaning they would go 1, 2, 3, 4 descending on the left side, then 5, 6, 7, 8 ascending on the right side. Is this correct? I wasn't able to find a layout for these two MOSFETs (3635? GA1R3? for PQB1 and 36354 A1T24 for PQB2)
2. Are the pins in the below pictures properly soldered? To my eye, it looks as if one pin on each component isn't connected to the board, as the solder seems to bubble up on the tip.
3. My resistances kept fluctuating while measuring them. For example, the Source to Drain for PQB1 varied from as little as 70 kΩ to as large as 8 MΩ. Could this be due to my leads? They're the regular AMES leads-- rather large for SMD pins. I just ordered needle-point leads, so maybe should I try measuring these resistances again? I made sure the power was off for the entire process, and the battery is disconnected, so am I doing something wrong in how I am measuring it?
Thank you for your time!
tantr13 <3
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