ES120 Electronic Screwdriver repair

[0xde4dbeef]

Hello Gentlemen,

I've got a miniware ES121 electronic screwdriver which turns out to have the board of an es120 (the predecessor model) which stopped working with a weird failure mode. I guess it would be a simple fix once I manage to identify the components.

Failure mode can be seen in this video: https://imgur.com/a/sSy0t2O.

Essentially what happens is I press the button, start turning the board so it would initiate the motor turning the same direction. Motor starts turning and quickly stops. On the bottom of the screen you can see an indication bar about how fast the driver spins. At the beginning the bar is full, when I press the button it becomes empty, if I rotate either direction it starts to increase and the motor starts spinning, until rather soon both the bar becomes empty and the motor stops. What is interesting is that when I disconnect the motor the bar stays empty and the screw keeps rotating in the direction I turn the pcb, indicating that the accelerometer is working just fine and the fault is to be found somewhere else ...

here's some pictures of the pcb with readable component marks:





The qfn above the stm32 labeled AGD2 would then be the accelerometer, which according to the findings above should also not be at fault.
The other 3 sots near the usb seem to provide power for the mcu, which works fine.
Due to the proximity of the battery connection I guess the 6 legged SOT IC with the inductor and two diodes just below the display and on the right side of the button is the charging circuit (which works fine)
Which leaves the Motor driver in the bottom portion of the PCB labeled MX630B which I found the chinese datasheet for: http://www.szxunrui.cn/siteimages/9904/2020041310424734.pdf

Has anyone done had this kind of problem/done repair to this device before?
From what I see here I guess it can only be the motor driver. I am kind of hoping to be able to find a drop-in replacement of better quality.
Any ideas, inputs or maybe spotted mistakes in my analysis would be very welcome! 

EDIT: I have just found that it is actually more likely that the suspected charging IC is actually a boos converter, since motor driver expects VDD in the range of 7.2V-9.6V. The markings of that IC are BC8nX, photo here:

[0xde4dbeef]

I think I found the part: https://datasheet.lcsc.com/szlcsc/1811151230_MST-MST9220BSF_C324586.pdf
If correct it's indeed a boost converter. The markings make sense (BCY1W2X3 Remark: 1=Production year, 2=Production week, 3=internal code) and the pinout seems to be reasonable.

[juston80]

Hi, I have the same problem.
How did you solve it by replacing the boost?

[phenix]

The same problem...
Dear 0xde4dbeef, please tell... did replacement of boost converter help?

[0xde4dbeef]

Unfortunately that boost converter has been unobtainable for me so I never got to try. Did you check if your screwdriver uses the same IC? Chances are miniware had to switch parts as well ...

[0xde4dbeef]

Since we're in lockdown again I decided to give it a go again, I happened to find a pin-compatible boost-converter (MP3221GJ-Z https://www.mouser.at/datasheet/2/277/MP3221-1384213.pdf). I adjusted the feedback circuit by replacing the 90,9kΩ resistor with two stacked 150kΩ resistors, which should result in 5.6V, so a little higher but within the 7V limit of the motor driver. Unfortunately the symptom remains the same. In the meanwhile I have also tried replacing the motor driver which also had the same result.

I'm wondering if maybe it's the gyro after all ...

[phenix]

Dear 0xde4dbeef, thank you for reply.

I own ES121 for almost 2 years, but I used it less than 3 "moto"hours. ~4-5 full charges. I've got a "glitch" under 1.13 firmware, later I upgraded to 1.14... (the glitch did not disapear.. it looks like engine was suddenly blocked after 0.5-2s. I downgrade to 1.10 and even 1.7a. It started to work again for a few minutes but with suddenly stops. Now situation is the following:
the same as seen on your video. Engine is not starting at all.

With disconnected engine it works like a charm...


Here are my corresponding photos:

[0xde4dbeef]

You say the behavior changed with different firmware versions?

[0xde4dbeef]

ok, since i find it highly unlikely that the firmware is at fault, i decided to look elsewhere. As the motor starts turning on mine but quickly stops, overcurrent protection came to my mind. Theres also a 0603 50mΩ shunt resistor on the board. So I hooked up the motor on my power supply and while it turned, it did not do so smoothly and it also consumed 0.6A @3.6V (hitting the current limit I've set) at no load, which obviously is way too much. So I guess after all this time it turns out the problem is not to be found on the pcb 

edit: i've disassembled the motor assembly and it turns out the gearbox is fine, it's really just the bare motor. guess it's time to find a replacement for this.

[phenix]

You say the behavior changed with different firmware versions?

Yes, previous firmware results a few minites of operation and sudden shut down. After that the device did not start. The usb cable was plugged and only after that I've be able to boot the device again. Now the engine is not working at all. When I did photos I unplug the engine. The pcb works fine... So, I have to test the engine. (Unfortunately, I cannot test it in my current location)

[lambdaknight]

You say the behavior changed with different firmware versions?

Yes, previous firmware results a few minites of operation and sudden shut down. After that the device did not start. The usb cable was plugged and only after that I've be able to boot the device again. Now the engine is not working at all. When I did photos I unplug the engine. The pcb works fine... So, I have to test the engine. (Unfortunately, I cannot test it in my current location)

I have this exact same problem and have been thinking of how to fix it, but I'm a electronics noob. It seems to most frequently shutdown when it finishes screwing a screw in and it hits resistance. And then it won't work until I plug it into USB and reboot it.

[phenix]

Today, I am not sure, but I bet that I'd got a problem with the motor. I am still not able to perform expository testing to be 100% sure. I do not have a spare engine here... but I tried to launch current es121 engine... it seems that it is in short circuit now. Too sad, because it is not big chances to find a replacement engine.

Consolation news... miniware launched es15

[0xde4dbeef]

ah yeah I just checked the ES15. Even more expensive, and their customer service has become worse every year. I've had a bunch of their products, most of them went bad and last time I contacted them, a "customer support agent" contacted me via a hotmail.com address and asked me to transfer money to his paypal account. After contacting miniware directly asking them what the deal was, they said the hotmail and paypal address  are indeed legit ... I don't think I'll by any new products from them again.

been trying to find a replacement motor without success so far, I have also contacted miniware to see if they'd sell me a replacement motor, but i've been waiting for "only" one week. I'll keep you updated.

[MrDob]

hello guys, I will have used the screwdriver 2-3 times, encountering the problem.
I thought it was the battery, I changed it with a 350mA one, nothing the problem persisted.
Gogglando, I came across your thread.
He enlightened me by finding the problem.
In practice it is sufficient to remove the 50mΩ resistor, which acts as a probe.
Removed and bridged the screwdriver will no longer have the problem.
I recommend with this modification it will not be able to break in case of strong mechanical resistance.

[nem0]

Thanks for this thread. My ES121 gave up after about a year. It was the motor. Contacted miniware and they did say they dont have any of the old model motors and it was especially made. After some hunting and ordering a few options of Aliexpress I found one that works. I did see a Minware ad for this screwdriver that said it was 20,000RPM so I tried to find a motor as close it this as possible.

FYI for anyone trying to fix motor problems with an ES121 I found that the following motor works well: https://www.aliexpress.com/item/1005001921128013.html you'll need to cut the shaft down a few mm. Heat the brass gear attached to the old motor with a jet lighter/torch to remove from the shaft, heat again to attach to the new motor.

[TorP]

Hi! I had a problem with my ES121 motor. It was drawing well over half an amp with zero load (connected to a lab psu). I opened it up by bending the metal tabs on the side and inspected the commutator under a microscope. It turns out there was metal filings in the gaps of the commutator. I cleaned the contacts with a glass fiber brush and that solved the problem. I wanted to share this if others have the same problem