Maker Pro
Maker Pro

Help revive dead Lanyu airpad

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
Hi forum friends,

Greetings! This Lanyu airpad model 910 was bought in 2016 and working good till i put in storage around late 2019. Today i took it out and switched on but there is no power led on. I plugged it to the 5v ac adapter for charging but there is also no charging indicator. I checked the ac adapter with my dmm, it shows 5vdc. I thought it must be the internal battery. After opening the case, the 3.7v internal battery measured zero. So i charged it but after 10 minutes, the battery was too hot as i can feel it is melting. I cut off this internal battery and connect to my other 3.7v lithium ion battery pack and start charging. But in less than few minutes, the battery red positive terminal expelled some visible smoke and i immediately shut it off. The external red positive battery terminal almost melted.
Fyi, when i use the dmm to check voltage on the board portion of where the ac adapter connects, i can only detect dc voltage of 0.3vdc as input. (refer image 092422) Is there some kind of component shorted somewhere to cause this? Hope someone with this sort of experience willing to share their views and help.
Thank you in advance.
 

Attachments

  • IMG_20210629_092125.jpg
    IMG_20210629_092125.jpg
    285.9 KB · Views: 11
  • IMG_20210629_092309.jpg
    IMG_20210629_092309.jpg
    273.5 KB · Views: 12
  • IMG_20210629_092422.jpg
    IMG_20210629_092422.jpg
    281.2 KB · Views: 11

Bluejets

Oct 5, 2014
6,065
Joined
Oct 5, 2014
Messages
6,065
A dead 3v7 (assume LiPo or similar) is dead and recharging should never be attempted once pd gets below approx 3.0V
As for the rest it is difficult to say from a distance.
 

Tha fios agaibh

Aug 11, 2014
2,242
Joined
Aug 11, 2014
Messages
2,242
You only read 0.3v because the battery is overloading your power supply. At low battery voltage, the current is exceedingly high.
That explains the smoke.

Try to isolate where the problem lies. Will it power up with battery removed and hooked to alternative power source?

Monitor the voltage and current its drawing without charger, and then again with it plugged in.

You may be able to recover the battery by first slowly charging it with around 3.5v and then put it back on the charger which should be around 4.2v.

Be careful around charging batteries they can blow up.
 

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
You only read 0.3v because the battery is overloading your power supply. At low battery voltage, the current is exceedingly high.
That explains the smoke.

Try to isolate where the problem lies. Will it power up with battery removed and hooked to alternative power source?

Monitor the voltage and current its drawing without charger, and then again with it plugged in.

You may be able to recover the battery by first slowly charging it with around 3.5v and then put it back on the charger which should be around 4.2v.

Be careful around charging batteries they can blow up.
With the original 3.7v lipo battery removed, i used another 3.7v lipo from a powerbank to switch on power. Still the airpad doesn't power up.
You are suggesting me to slowly charge the battery around 3.5v, but how do i do it with a 5vdc charger? Is it ok to connect some sort of resistor to the positive side of the charger to get that 3.5v...or any other method? Kindly assist me here.
Your assistance is highly appreciated.
 

Tha fios agaibh

Aug 11, 2014
2,242
Joined
Aug 11, 2014
Messages
2,242
Initially thinking the battery was problem.
Possible short?
So, You hook up your 3.7v battery and its voltage quickly gets drained to near 0v?

Try feeling around for overheating components like chips or diodes with your finger.
Don't leave hooked up for more than about 10 seconds while trying this.
Measuring current its drawing.
 

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
Initially thinking the battery was problem.
Possible short?
So, You hook up your 3.7v battery and its voltage quickly gets drained to near 0v?

Try feeling around for overheating components like chips or diodes with your finger.
Don't leave hooked up for more than about 10 seconds while trying this.
Measuring current its drawing.
As the original 3.7v 3200mAh lipo battery was cut off and kept aside, i plugged in the 5v ac adapter and still barely get 0.3v dc at the input connector. Unplugged the ac adapter and i use my dmm diode test on D1 the one nearest to the dc input connector. The diode reading on dmm is about 32ohm both ways. Suspect this is bad.The diode is marked SL. To verify this, i also did diode test on D17 and D25 and they are reading about 195 ohm on one side and "1" infinite the other way. Normally this is ok.
Is there any way to identify what type of diode is the bad one and if there is any substitute since the stock i have are the bigger standard through hole type like 1N4007.
 

Attachments

  • Screenshot_2021-06-30-09-56-52.png
    Screenshot_2021-06-30-09-56-52.png
    368.1 KB · Views: 2

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
Done a 15 minute recharging the original 3.7v lipo battery, then i attached temporarily to the airpad battery connector for less than 10 seconds to check for overheating components. Too bad there is none. When i use dmm to measure the dc voltage on battery, it reads around 3.7vdc but almost zero at the airpad battery connnector. What seems to be the reason this happens?
 

Attachments

  • IMG_20210630_111938.jpg
    IMG_20210630_111938.jpg
    259.4 KB · Views: 3

Tha fios agaibh

Aug 11, 2014
2,242
Joined
Aug 11, 2014
Messages
2,242
The diode reading on dmm is about 32ohm both ways. Suspect this is bad.The diode is marked SL.
Perhaps ot enough power or time for my finger burn test. Lol

Unsolder and test the diode out of circuit to confirm its condition. I suspect it's a Schotty 1N5819 SOD123
 

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
Perhaps ot enough power or time for my finger burn test. Lol

Unsolder and test the diode out of circuit to confirm its condition. I suspect it's a Schotty 1N5819 SOD123
Today i unsoldered the suspect diode and test it out of circuit and it reads 196ohm one way and "1" the other way. So, this diode at D1 still good. What other test i can perform to check for bad component? It looks as if now the airpad is completely dead. I plugged in the original lipo battery( charged externally to 3.7vdc) and at the same time plugged in the 5vdc adapter. Pressed the power switch on the airpad and the volume key simultaneouly for hard reset. But nothing comes out.
Now there is no more smoke or overheated component.
Hope that this airpad still can be rescued.
 

Tha fios agaibh

Aug 11, 2014
2,242
Joined
Aug 11, 2014
Messages
2,242
Be prepared it may take considerable time to trace it down and often you may find that the suspect part cannot be Id'd or sourced.

You can remove components that are tied along power rail and then monitor voltage or resistance to ground to see if short goes away. When you remove a component, check to see which side (upstream or downstream) the short remains.

Another method is briefly injecting voltage with a regulated power supply after covering pcb with isopropyl alcohol and then watching where the alcohol reacts to heat caused by current flow.

Good luck.
 

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
Be prepared it may take considerable time to trace it down and often you may find that the suspect part cannot be Id'd or sourced.

You can remove components that are tied along power rail and then monitor voltage or resistance to ground to see if short goes away. When you remove a component, check to see which side (upstream or downstream) the short remains.

Another method is briefly injecting voltage with a regulated power supply after covering pcb with isopropyl alcohol and then watching where the alcohol reacts to heat caused by current flow.

Good luck.
The second option of covering pcb with isopropyl alcohol seems to be easier for me. What sort of regulated dc power will be suitable, like around 3vdc...or up to 5vdc? Fyi, i have a manual adjustable dc output power supply which outputs from 0-12v dc. Instead, will it be ok if i used the factory given ac adapter which output 5vdc for the testing?
 

Tha fios agaibh

Aug 11, 2014
2,242
Joined
Aug 11, 2014
Messages
2,242
I would use your adjustable ps. Just don't exceed voltage rating of what your powering.
You can learn a lot from the web.
Here's a couple examples courtesy of YouTube.


 

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
I would use your adjustable ps. Just don't exceed voltage rating of what your powering.
You can learn a lot from the web.
Here's a couple examples courtesy of YouTube.


Very interesting and informative videos. I find the second video much more applicable and easier to understand. Will definitely try out the voltage injection using my manual adjustable dc power supply.
Appreciate your help. Thank you so much.
 

mikey5791

Jun 7, 2013
174
Joined
Jun 7, 2013
Messages
174
By briefly touching for less than 10 seconds the li ion battery connector to the airpad battery connector, i try the finger touching method to see which component is overheating.
Finally, i noticed one square ic labelled AXP192 is hot to touch. It is a power management ic. Anyone know how to check if this ic is bad? If it is bad, can this be the faulty component causing the airpad not starting?
 
Top