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6 Posts

12-07-2018

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Edge 2-1580 oscillates between charging and not charging

2018-12-08, 0:34 AM

I'm working on a friend's laptop that stopped taking a charge several months ago. When the power adapter is plugged in, it will quickly change between "charging" and "not charging." This is apparently a common problem with models that use this motherboard; see the following threads:

 

Edge 2-1580 Laptop won't charge

Lenovo Edge 2-1580 battery charging issues

Lenovo Edge 2 - 1580 Oscillating between Charging and Not Charging

 

Battery Not Charging on Flex 3

Flex 5 - Laptop not charging

Lenovo Flex 3 1480 charging issues

 

There are several more that are potentially related, but it's unclear from the original post. Anyway, here's what I've tried:

  • Ensuring Windows 10 is fully updated
  • Updating the BIOS to the newest version (required editing one of the files in the download in Notepad to remove the requirement for 30% battery while I was able to get the laptop to run on only the AC adapter)
  • Installing all updated drivers available on the Lenovo website
  • Replacing the AC adapter
  • Replacing the battery
  • Running Lenovo diagnostics (all passed)
  • Checking the motherboard for hot, short circuiting components (there are none)
  • Tracing the charging circuit from the battery upstream until I find a component that seems to be broken

This last one may have paid off: I found that at a chip on the back (top when the board is mounted in the case and the laptop is upright) the voltage drops from 19V to 0.4V, which is what I'm seeing on the positive terminal of the battery. It seems to be an Alpha Omega AON7410 MOSFET. I'm currently looking for a place to buy one. Digi-Key has them for 62¢, which would be much better than the $712(!!!) that Lenovo wants for a new motherboard, or even a used one elsewhere. Has anyone had any luck fixing this problem?

 

Picture of the chip's location: https://postimg.cc/0MZVD4FX

 

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6 Posts

12-07-2018

United States of America

7 Signins

180 Page Views

  • Posts: 6
  • Registered: ‎12-07-2018
  • Location: United States of America
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Re: Edge 2-1580 oscillates between charging and not charging

2019-04-08, 3:25 AM

Final update:

 

After a long break, I took another stab at fixing this laptop, and unfortunately I've determined that this problem is not repairable. The battery is charged by a circuit called a synchronous buck converter, which steps the voltage down from input (20V) to charging voltage (probably around 7V). When I replaced the MOSFET, I was only seeing 5V at the drain (battery power supply). That's enough to run the laptop, but not enough to charge the battery.

 

After doing some research and learning about how MOSFETs, buck converters, and synchronous buck converters work, I determined that the problem was not a faulty MOSFET, but a faulty microcontroller. In the picture in the first post, the Nuvoton chip is a microcontroller that seems to control the buck converter, among many other things. It changes the voltage going to the gate on the two MOSFETs at a frequency of several kHz (I assume; I didn't have an oscilloscope to look at it with), and the pulse width of the signal going to the first MOSFET (the one I replaced) has to be slightly wider than that of the signal going to the second MOSFET. This signal seems to be present, since the circuit is functioning, but degraded, since the voltage output is too low and every other component in the circuit I tested was functional.

 

The Nuvoton microcontroller doesn't have any data sheets I could find online to confirm if I had the right pin, but I was at least able to confirm continuity between a pin on the microcontroller and the gate of the first MOSFET. It seems that the microcontroller has been degraded over time, and without Lenovo's firmware to flash to it, there's no way to replace this chip. You could pull one off an old Edge 2 motherboard, but it's likely just a matter of time until it fails too. Time to buy a new laptop.

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6 Posts

12-07-2018

United States of America

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  • Message 2 of 4

Re: Edge 2-1580 oscillates between charging and not charging

2018-12-18, 1:34 AM

Update:

I've got a few of these MOSFETs from Digi-Key and successfully replaced the (apparently) faulty one. These have a different secondary number than the original chip - GA5S5B on the original, GA722X on the new ones - but a search for GA5S5B turned up nothing. "7410 MOSFET" only turned up these AON ones, which seem to be the same design as the old one.

 

After replacement, I'm now seeing a voltage of about 5 volts between the new chip and the second one next to it in the picture (I believe this arrangement is called a buck converter) when the laptop is plugged into the AC adapter and the battery is not plugged in. This isn't enough to charge the battery (it just maintains its charge, probably discharging at a very reduced rate), but it does fix the screen flickering problem caused by the computer shifting between charging and discharging. When reassembled and turned on, the laptop will report "Plugged in, charging," even though the charge will never increase (it never decreased either during my testing, FWIW). I'm thinking there's some other circuit element that's gone bad in addition to the MOSFET, but can't tell what it would be.

 

According to what I could find (see the diagrams on page 2), there should be an inductor and a capacitor between the buck converter output (or some equivalent if this is a representation of multiple circuit elements). The main problem is that V_out isn't high enough; it needs to be more like 12V. This could be caused by a few things:

  • A faulty low-side MOSFET, the 7506 chip in the picture on the first post. It's not shorted, so I don't think it's the problem.
  • A faulty component on the other side of the motherboard. Possible suspects, in order from first to last along the circuit:
    • Gray block PL4401 (inductor?), has continuity so it's not burnt out, but maybe the inductance has gotten out of tolerance
    • Black rectangle PG4412, marked R010, no idea what this does, but it has continuity across it.
      • After some research, I think this is a resistor. R010 indicates a 0.01Ω resistor, which is too small for my multimeter to measure, but on the most sensitive (200Ω) scale, it registers as 0.4Ω, so maybe this resistor has degraded and has too high of a resistance.
    • Three capacitors, none of which is shorted so they probably aren't bad
    • White block marked 10, probably a fuse, has continuity across it so it's still good if it's a fuse.

Can anyone shed some light as to what the gray block and black rectangle are?

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6 Posts

12-07-2018

United States of America

7 Signins

180 Page Views

  • Posts: 6
  • Registered: ‎12-07-2018
  • Location: United States of America
  • Views: 180
  • Message 3 of 4

Re: Edge 2-1580 oscillates between charging and not charging

2019-04-08, 3:25 AM

Final update:

 

After a long break, I took another stab at fixing this laptop, and unfortunately I've determined that this problem is not repairable. The battery is charged by a circuit called a synchronous buck converter, which steps the voltage down from input (20V) to charging voltage (probably around 7V). When I replaced the MOSFET, I was only seeing 5V at the drain (battery power supply). That's enough to run the laptop, but not enough to charge the battery.

 

After doing some research and learning about how MOSFETs, buck converters, and synchronous buck converters work, I determined that the problem was not a faulty MOSFET, but a faulty microcontroller. In the picture in the first post, the Nuvoton chip is a microcontroller that seems to control the buck converter, among many other things. It changes the voltage going to the gate on the two MOSFETs at a frequency of several kHz (I assume; I didn't have an oscilloscope to look at it with), and the pulse width of the signal going to the first MOSFET (the one I replaced) has to be slightly wider than that of the signal going to the second MOSFET. This signal seems to be present, since the circuit is functioning, but degraded, since the voltage output is too low and every other component in the circuit I tested was functional.

 

The Nuvoton microcontroller doesn't have any data sheets I could find online to confirm if I had the right pin, but I was at least able to confirm continuity between a pin on the microcontroller and the gate of the first MOSFET. It seems that the microcontroller has been degraded over time, and without Lenovo's firmware to flash to it, there's no way to replace this chip. You could pull one off an old Edge 2 motherboard, but it's likely just a matter of time until it fails too. Time to buy a new laptop.

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3 Posts

08-02-2019

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  • Registered: ‎08-02-2019
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  • Message 4 of 4

Re: Edge 2-1580 oscillates between charging and not charging

2019-08-02, 18:30 PM

In researching this issue I read where someone just charges the battery(s) from a bench power supply. This solves some issues and might be good enuf. Lipo batteries need balancing and I wonder if the microcontroller performs this function.

 

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