Lithium Battery Capacity Meter simple repair. Need hints

Thread Starter

aacman

Joined May 17, 2020
16
Hello
I am just a hobbyist and have some interest in electronics and have built 18650 battery packs, arduino iot projects, etc

For harvesting old 18650 Lithium-Ion cells, got a Capacity tester named HW-586 (a copy of another popular ZB2L3 ).
Its a simple analyzer which using power resistor load and it worked fine for days. It works on microusb 5V.
i forgot its max Voltage is 15V and connected its battery terminal to a 25V power supply (just was checking Voltage as my multimeter was bit far. Didn't try to discharge a power supply) and within 3 seconds/so, some minor smoke came out of it.
I immediately disconnected but its not working properly, Voltage reading is 0.5 volt less than actual of any battery it measures and not showing ampsHour and Amps reading at all (Just zero)

The circuit is simple and on side of board. I tried checking visually but could not find any burnt thing.
Can someone help me find what got toasted? I might have some spare components from other circuits around. I can test using multimeter and have soldering skills. Someone told me to check all resistors, i tried and they all measured fine, as per labels (Do not want to but another one and lot of wait to get another)
Thanks very much


Link has all the details if you want to take a close lookup of circuit
https://www.aliexpress.com/item/32840907639.html
https://www.amazon.com/Comimark-1-5v-12v-Capacity-Discharge-Lead-Acid/dp/B07YHZMZ88/

image1.jpg
 

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MrSalts

Joined Apr 2, 2020
2,767
once smoke is emitted from an electronic component, it will not generally work again. You have either damaged the voltage regulator (labelled 117j and/or the microcontroller on the back side of the board. If the microcontroller is damaged, you'll need to program it to read the voltages, convert the ratio metric ADC value to a readable number and display it on the 7-segment LEDs. How much do you want to invest in a repair? What kind of programming are you comfortable with? Do you have a way to download a program to a microcontroller (a programmer)?
 

AlbertHall

Joined Jun 4, 2014
12,396
The 1117 regulator would be my first suspect as its maximum input voltage is 15V. You could check the output voltage of this regulator and replace if faulty.
 

Thread Starter

aacman

Joined May 17, 2020
16
once smoke is emitted from an electronic component, it will not generally work again. You have either damaged the voltage regulator (labelled 117j and/or the microcontroller on the back side of the board. If the microcontroller is damaged, you'll need to program it to read the voltages, convert the ratio metric ADC value to a readable number and display it on the 7-segment LEDs. How much do you want to invest in a repair? What kind of programming are you comfortable with? Do you have a way to download a program to a microcontroller (a programmer)?
Thanks for the reply :)
1. Actually there are no components on back side.
image3.jpg


2. i zoomed in on 117 and its a AMS117 3.3 DNJT written on it. I searched and it a linear voltage regulator. Are you sure thats defective? What about 8205 and 321? they look like transistors, can they damage too?
3. Yes, i have soldering skills. Since i have arduino and some other programmers, yes i think i can program them or learn to :) I might have a AMS117 from some other defunct things lying around. Yes i can solder smd's too.(basic skills). Its a hobby and i feel its a small circuit and if someone can guide me i will repair it given its not completely dead and i will learn something interesting in process. I also follow repair-reuse-recycling lifestyle :)

4. Important
Just to be sure i am not confusing you, i did not apply 25V to module's input (i.e. 5v microusb), I connected power supply (just for few seconds to measure power supply's output voltage) to the battery testing ends of module(left side; see picture below) . I did not start discharging (a power supply) though using module settings ofcourse, just connected.

image 3.png
 
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MrSalts

Joined Apr 2, 2020
2,767
Where did the smoke come from? Transistors can usually handle 25v or more volts. It was either the 1117, or the microcontroller that measures the voltage and drives the display. The microcontroller likely has a voltage divider (pair of resistors) to bring the measured voltage (0-15v) down to 0-3.3v range. Since the microcontroller is not on the back, they put a bunch of vias in the board and hide the microcontroller under the display. The microcontroller is a tiny chip - look at the vias and traces behind the display.

With the voltage divider, the ADC in the microcontroller was likely exposed to 5VDC. Not a huge surge that would absolutely cause smoke but, who knows? That's why my first guess is the 1117 voltage regulator.
 

Thread Starter

aacman

Joined May 17, 2020
16
Where did the smoke come from? Transistors can usually handle 25v or more volts. It was either the 1117, or the microcontroller that measures the voltage and drives the display. The microcontroller likely has a voltage divider (pair of resistors) to bring the measured voltage (0-15v) down to 0-3.3v range. Since the microcontroller is not on the back, they put a bunch of vias in the board and hide the microcontroller under the display. The microcontroller is a tiny chip - look at the vias and traces behind the display.

With the voltage divider, the ADC in the microcontroller was likely exposed to 5VDC. Not a huge surge that would absolutely cause smoke but, who knows? That's why my first guess is the 1117 voltage regulator.
I tried finding but was not able to understand where the smoke came from. Please note that (not to cause confusion), The module turns on fine with 5v usb input, even shows voltage of a connected battery (0.5 V lesser than actual) but not showing any ampsHour and Amps reading (look at top right of module) Just shows zero on screen, when we select those options via push buttons

1. I checked the AMS117 using multimeter after powering on the module via regular 5v usb and its input shows 4.85 and output pin as 3.86V. Is it Ok then?
2. Yes usually these displays have some chip/IC behind it (i have one display separate so have seen it). So is that microcontroller and it can be affected too? perhaps hidden between Display and PCB
3. As per the back side of PCB< there are 6 pairs of contacts, perhaps thats of microcontroller and display combined. I dont know how do i test it? :( i can desolder ofc if one can help me check. Quick look tells me its just prongs of matrix. I dont know where is microcontroller. Here i a video about this..if u can have a quick look on its anatomy
3. I have these modules lying around, with same 3461AS-1 matrix label. can i replace microcontroller or components from this to repair it?
https://www.aliexpress.com/item/1005004657032241.html

Thanks for the help guys
 

MrSalts

Joined Apr 2, 2020
2,767
If the display is showing a recognizable number, the output of the microcontroller is working. The input pins related to amp-hours seem to be having trouble. Maybe you popped...
- the "burden resistor" that is used to measure current (voltage / resistance = current). Or,
- an op-amp that amplifies the voltage drop across the burden resistor. Or,
- the input pin on the microcontroller for the ADC that measure the voltage at the burden resistor.

I don't know how much work you want to put into this but, I'm kind of running out of steam trying to fix a $9 item.
 
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Thread Starter

aacman

Joined May 17, 2020
16
If the display is showing a recognizable number, the output of the microcontroller is working. The input pins related to amp-hours seem to be having trouble. Maybe you popped...
- the "burden resistor" that is used to measure current (voltage / resistance = current). Or,
- an op-amp that amplifies the voltage drop across the burden resistor. Or,
- the input pin on the microcontroller for the ADC that measure the voltage at the burden resistor.

I don't know how much work you want to put into this but, I'm kind of running out of steam trying to fix a $9 item.
1. Good to know "microcontroller is working"
2. which one is "Burden resistor"? R020? I did test all resistors using "Kaiweets HT118A Digital Multimeter" from both sides and it measured same as labels. Can you send a link/tube video which teaches to check resistors well?
3. Which one is "op-amp" and how do i test it?
4. "the input pin on the microcontroller" is input pin part of MC or some other part?how do i test it?

Sorry if you are getting bothered by my messages. I know its cheap but its actually not about $9 only..but i live quite far from town and it takes time to get this by shopping online. Also as you can see quite a part of module working fine so i feel i can repair it and learn something in process. Also i follow reuse-recycle concept in life, so avoid generating too much waste
Kindly bear with me
 

Thread Starter

aacman

Joined May 17, 2020
16
The 1117 regulator would be my first suspect as its maximum input voltage is 15V. You could check the output voltage of this regulator and replace if faulty.
I checked the AMS117 using multimeter after powering on the module via regular 5v usb and its input shows 4.85 and output pin as 3.86V. I guess its ok. MrSalts also guess the same. Can you have a read the above few updates.. may be you can help me find the defective thing
Thanks
 

Ya’akov

Joined Jan 27, 2019
9,264
If you observed smoke then something let it out. This means there will be some visible sign of it. It could be a surface crack on an IC or other component. Using magnification, inspect each component for some sign. It is possible the defect is underneath a component and so invisible but my experience is the construction of the chips being designed to allow heat to radiate away, catastrophic failures happen on top.

If somehow it happened on the bottom, there would be a sign on that as residue on the PCB. If there was smoke, my first line diagnostic would be visual inspection.
 

Thread Starter

aacman

Joined May 17, 2020
16
If you observed smoke then something let it out. This means there will be some visible sign of it. It could be a surface crack on an IC or other component. Using magnification, inspect each component for some sign. It is possible the defect is underneath a component and so invisible but my experience is the construction of the chips being designed to allow heat to radiate away, catastrophic failures happen on top.

If somehow it happened on the bottom, there would be a sign on that as residue on the PCB. If there was smoke, my first line diagnostic would be visual inspection.
Thanks for reply but i did check for it (as i wrote it in first post). Yes even used magnification but could not find anything.
Perhaps because LED and module is working visibly and given it was very little smoke. I seriously went ahead and took high res pics of module too but there is nothing to post as they are as same as shop site pics i posted above. I can still post if that helps.

Can you kindly help me with testing/finding the component after the few things we ruled out here?
https://forum.allaboutcircuits.com/...-simple-repair-need-hints.192097/post-1802224
Thanks
 
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