Asus E410 only works on battery after reverse polarity

[Kervin Mathumbu]

With the help of the schematic for board R3.1 (mine is R3.0), I located the said resistor near the charging jack. Interestingly, it is near the mosfet that had 0.02 on source and drain. And 0.09 source and gate. With my meter set to 20k resistance, I get 3.94 reading. Is this equivalent to the 4k expected or it's way off?


I am now trying to test the tantalum cap and should feedback on it as well.

[Kervin Mathumbu]

With my meter still on 20k, I get no reading from the tantalum cap. Or might I have configured my meter incorrectly? Someone said to could test by shorting the cap as well. I plugged the AC and then short it accordingly but got no spark at all. Might this confirm that the cap is bad as suspected? What seems to be an equivalent replacement is near $2 at my local mouser I found.

[Kervin Mathumbu]

Tested the same tantalum on my working laptop and also got no reading. So likely I am not testing it correctly I also tested the pin4 resistor and got the same 3.9 reading. And there is 18v passing through it unlike my broken board which only has 3v. Also the mosfet on the working laptop has 23.9v at its gate. Unlike my broken one which has 0.09v

Where might I go from here. Or how am I to best test the tantalum from my DT-830B meter?

[mon2]

Is there a hole in this tantalum capacitor? If yes. It should be replaced.

Yes it appears you have found the 4K resistor. Have the mosfet pics and part numbers been posted?

[Kervin Mathumbu]

Sorry I had missed your reply. The tantalum looks clean but I have some findings you could make something out of.

I have now located both mosfet near the said resistor. One that is further from the currency sensor have 18v going into it. But has a 3v at the gate. Therefore what should be the 2nd mosfet has 3v at source and 3v to gate. Might this mean a shorted 2nd mosfet?. I shall get the part numbers from the schematics. My wife has a clever camera phone but I do not. The 2nd mosfet is the same one with odd resistance of 0.02

[mon2]

It is important to share the full details otherwise the case will take much longer to resolve.

Meter in resistance mode.

Measure the resistance of the mosfet:

source (1-2-3) & drain (5-6-7-8) ; place a meter probe on any pin of source group / other probe on any pin in drain group
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each resistance with units of measure in ohms. Not sure what 0.02 means. Take pics of the meter face if required to post here.

Measure each of the mosfets. From the measurements we can determine if the mosfet is defective or not.

Units of resistance will be ohms; kohms (thousands of ohms); Mohms (mega ohms). The units are important to note.

From the earlier pic of the tantalum capacitor - it does appear to be defective and has a hole on the top surface. Post more pics of the same part.

[Kervin Mathumbu]

Okay I was measuring in diode mode. Let me do in resistance mode. You right it looks like a hole but actually a marking or so. The picture I shared is from someone here who had a bad battery case. So his tantalum had that hole-like mark and so does mine it appears.

[Kervin Mathumbu]

1st bigger mosfet is part number: PQ8901

2nd mosfet: PQ8902

[Kervin Mathumbu]

With my meter function set to 200k res range, the first mosfet keeps counting up (was near 200.0 at some point). The 2nd mosfet start from 01.0 and within a second or so counts down to 00.0

Assuming the 2nd mosfet is shorted?

if so, can I temporally jump it until I have a replacement? I understand it could be risky but I am to run the PC without a battery (since they both last locked up after years of use) and so I hoped it could perhaps work to my advantage somehow. I will understand if the battery's absence will on the other hand only amplifies the risk - and gladly wait for the replacement part.

[mon2]

Need all of the requested measurements.

[Kervin Mathumbu]

Sorry let me go through your directives again. I actually thought I got them all. Should post back shortly.

[Kervin Mathumbu]

When set to 2000K resistance range, the 1st mosfet counts up to about 730 (it seems) and then start counting back slowly. The 2nd mosfet counts back from around 050 to 000 within some 2 seconds or 1 and then stay there. The screen will show 725 for example with no decimal at all. It is the cheap DT-830B so perhaps it is very limited.

[mon2]

Post # 26.

[Sephir0th]

And get rid of the 200K range please. Way to high to detect a real short-circuit. 200 (without K) Ohms range works perfectly fine for most of the cases.

I'm convinced, one of the DC-IN Mosfets is the origin of your issue as already more or less confirmed in post #14. but to confirm and to solve that, we need to stop moving in circles right now.

[Kervin Mathumbu]

To the best of my recollection the meter (in resistance mode) would not display a reading for any of the two mosfets unless I set it to 200k or 2000k but I shall retry this to confirm. Post#14 was done in diode or continuity mode but I see I went on to infer to the readings thereon as resistance (instead of voltage drop?) in some of my succeeding posts (my bad - I am admittedly a newbie in these, trying to fix my own mobo). As suggested, I shall retry measuring at a 200 range first and then feedback.

Sephir0th
Yes, those are the mosfets I am testing. And the smaller looking is the one which had 0.02 reading in diode mode.

[Kervin Mathumbu]

Smaller mosfet has a reading of 02.0 when set to 200 range. Bigger mosfet will only have a reading from 200k range - counting up front around 35.0 going up.

[Sephir0th]

The "smaller" Mosfet is internal shorted and need to be replaced. After that the board should work again.

And no 200K range anymore with laptops!

[Kervin Mathumbu]

Trying to take it out...

[Kervin Mathumbu]

Tons of thanks to all of you guys - more specially Sir mon2 who walked with me (a newbie) from start to bingo with handy pointers.

Short version: Laptop now working with a bypassed mosfet (yes, I understand the inherent risk and can only hope in God's mercies and goodness that the spare part will find the laptop still in one piece).

Long version: After failing to cleanly remove the mosfet with a soldering iron and added solder, I had to carefully scratch up the black part of the mosfet with a pin, and broke it further with a long nose. After uncovering the greater part of the internal plates I applied solder and then the plates slid off.

Connected drain and source and then went to analyze this (again): https://electronics.stackexchange.co...l-in-a-laptop#

When the risk seemed somewhat calculated, I plugged in the AC and the PC came on.

Still not know if being without a battery has a positive implication for my situation (or that makes no difference).

A tip on what the key factors/properties to keep in mind are when ordering a replacement mosfet would be greatly appreciated, please. Or do I take the schematics part number and provide Asus South Africa with it (a more cost effective route is admittedly preferred)?

Again many thanks for all the help!

[piernov]

Connected drain and source and then went to analyze this (again): https://electronics.stackexchange.co...l-in-a-laptop#

When the risk seemed somewhat calculated, I plugged in the AC and the PC came on.

Except that this answer is not related to the question that was asked. The answer is about the protection MOSFETs of the BMS, which is the circuit on the battery itself, whereas the question was about the DC-in MOSFET of the charging circuit, which is on the motherboard.
Both circuits have back-to-back MOSFETs, but they do not serve the same purpose.
The DC-in MOSFETs act as an overcurrent protection by switching off the reverse MOSFET when the current flowing through the DC-in current sense resistor is too high.
The DC-in MOSFETs act as an undervoltage protection by switching off the reverse MOSFET when the input voltage falls below a certain threshold (either normal if AC adapter is unplugged, or abnormal due to defective AC adapter, too much current draw on the AC adapter that hasn't entered protection yet or too much resistance, all of which could cause further catastrophic issues).
Similarly, the DC-in MOSFETs also act as a reverse discharge protection by turning off the forward MOSFET when the AC adapter is unplugged from the wall but still connected to the machine, so that the battery does not discharge into it.
The DC-in MOSFETs can act as an inrush limiter, which means limiting the amount of current flowing when the main power rail is completely discharged (that current can be high because there's a lot of capacitance with low impedance on this rail) by turning the reverse MOSFET on gradually.

So no, I cannot say that bridging a MOSFET is a reasonable idea. It'd be even worse to do that on the BMS circuit of the battery itself btw.

Since the failure happened after a reverse polarity event, it sounds like an even worse idea to bypass protections now.