Fixing a trash-picked Acer Aspire E1-731

1146 words, estimated reading time: 6 minute(s)
Originally published on June 11, 2025
Last modified on June 11, 2025

Recently I found an Acer E1-731 on a random junk pile. At a first glance it seemed relatively modern (which I concluded from the presence of USB 3.0), but also heavily water damaged. While most would conclude that it cannot be saved at that point, I decided to take it with me anyway to see if there’s anything worth salvaging and try to repair the laptop itself.

First impressions

The first thing I did upon taking the laptop was to remove the main battery, as any current would massively speed up corrosion of the board. Once the laptop was at my workstation, I took off the bottom cover and found that what had been exposed of the motherboard was unsurprisingly rather dirty, but there was no corrosion to be found.

With the back cover gone I was able to remove the 4GB DDR3 SODIMM, 500GB WD Blue hard drive and an Atheros WiFi card, which were then dried and the SODIMM and WiFi further cleaned up with IPA and again dried. With these aside, I continued disassembling the laptop to dry everything as quickly as possible and also to remove the RTC battery (for the same reason as the main battery). Not coincidentally, there were a few small corroded areas around the RTC battery socket, but besides that the board was in pretty good shape.

With all of the parts dried and therefore safe from any further corrosion, I decided to test the salvaged RAM and HDD. Both ended up working and the HDD is also perfectly healthy (judging by the reallocated sector count, which is 0), which alone made picking up this laptop worthwhile. The main objective however was to repair the laptop itself, so then I proceeded to have a look at the motherboard itself.

Diagnosing the board

After having made sure that the board was dry and clean of corrosion, I detached the DC in jack and power button from the bottom case and hooked them up to the motherboard to give it a test boot. However, it gave no signs of life: no LED lit up at all and pressing the power button also did nothing.

My first action was to measure the voltage at the power button header and I found that it was abnormally low (~300-400mV for a signal meant to be 3.3V). After some more probing around I found out that the main rail was also gone, which I traced down to the DC in circuit. To be more specific, it seemed that something was wrong with the DC in MOSFET as its drain was at the expected ~20V, but the source at just ~900mV.

At this point, I needed schematics and a boardview, as the board itself is devoid of any component markings with the exception of screw holes and connectors. Fortunately, they were rather easy to find (“VA70/VG70 rev 2.1 schematic boardview”) and so I proceeded to ask and search around to see what could be going wrong. I first checked the downstream VRMs for any shorts or overloads which were said to potentially cause this, but I found nothing. Next, I went through the charge controller circuit as suggested by a certain forum post, but also found nothing wrong there.

Eventually, I had a look at the 2nd DC in MOSFET (Q8802), right between the 1st one (Q8800) and a battery charging MOSFET. I have found that the R_DS(off) of this MOSFET was just about ~500Ω, which I suspected to be extremely low considering a enhancement-mode MOSFET is not meant to conduct at all while off. I desoldered this MOSFET and when powering the board again, there was ~20V on both the drain and source of the 1st DC in MOSFET.

From that and the apparent fact that nothing was wrong downstream, I concluded that the 2nd DC in MOSFET was faulty and needed a replacement.

Sourcing a replacement MOSFET

I decided to buy the replacements from AliExpress as usual. There is, of course, a risk of getting fakes, but in this case the MOSFETs I bought are genuine. Specifically, the MOSFET in question is an IRFHS8342, and I bought the replacements here.

Replacing the MOSFET

After the MOSFETs arrived, I soldered one onto the board. The specific procedure I used was to tin the pads with my iron in advance and apply flux liberally before applying hot air.

When I plugged in the board (after letting it cool down, of course), it would click at a regular interval and otherwise show no signs of life. This was still progress, so while remaining cautiously optimistic I made a few more measurements around the board. The main rail voltage had now gone up to oscillating at around 4V, which could suggest that there’s a VRM being overloaded, but just like the previous time I found no shorts anywhere.

While desoldering the dead MOSFET, I had accidentally knocked two capacitors between it and the other MOSFET (C8802 and C8803) off the board. Just to rule out these two causing issues, I went ahead with soldering these two back on. C8802 was soldered on easily, but on the other hand I dropped and lost C8803 while trying to solder it back on. Nevertheless, with C8802 again present the board finally powered up!

For reference, here’s these 2 capacitors in the schematic:

With the board finally showing signs of life, the only thing remaining to do was to check whether it outputs an image. I initially tried HDMI, but there was no output at all. On the other hand, with the internal display connected it POSTed straight away. From here it was simply a matter of installing a new RTC battery and reassembling the laptop.

Final words

The laptop now runs well, but not without flaws. The water had sadly not been kind to the display and as a result the light guide is visibly distorted, which doesn’t really have an impact on usage but isn’t nice to see either.

The main battery was found to be dangerously discharged (~1.4V per cell), however the BMS successfully revived it and reports a full charge capacity of ~30Wh with a design capacity of 48.4Wh, leading to a wear level of around 39%. A battery calibration together with time will reveal whether this figure is true, but I am nevertheless exceedingly happy to have a working battery.

Finally, I believe that the clicking thing serves to confirm the importance of replacing dead filter capacitors. Even if the board booted without C8802, it’s not impossible that there would have been stability issues later on. I have since found C8803 again, however I will probably not disassemble the whole laptop again just to solder it back on. If I do end up tearing it down again for another reason or the laptop shows any instability, I will take the time to solder it back on.