Laser Level Charger PCB ID

[Shaky]

Hi all. I have had a look at a battery pack out of a Datum NE-1L Laser Level for a mate that isn't powering the device. The cells are 2 x 26650 Li-ion in parallel and test fine. However, they don't output any power and also won't charge. The LED is a 2-colour unit, the green is OK (charging complete presumably) but the red (charging in process presumably) tests short circuit. When the wall-wart is turned on, it is outputting the correct voltage but the LED's on the battery pack don't illuminate. It's pointing to the charger/bms unit being faulty I'm guessing.

Trying to get hold of a replacement pack is proving fruitless (and expensive if they were available) so I decided to see if I could source a replacement/compatible charger PCB. However, there doesn't appear to be many markings on the board that result in any suitable results from Google etc so I was wondering if any of you guys here could point me in the right direction, or am I fighting a losing battle ?

Pics uploaded of course 

TIA.

[globoy]

No wonder the replacement packs are expensive.  That's a complex battery controller PCB.  It's custom, so you aren't going to find an off-the-shelf replacement.  It uses an off-the-shelf TI BQ24296M charge controller https://www.ti.com/product/BQ24296M, a low-end STM32 ARM micro-controller https://www.st.com/en/microcontrollers-microprocessors/stm32f030f4.html, and some other circuitry, at least some of which appears to be a small buck or boost converter.  Looks like the STM32 controls the LED. 

I'd first take a close look for things like a bad/loose solder joint, bad wiring harness connection or corrosion somewhere that might be causing enough of a short to cause a failure.  Then things you might start with to debug this PCB are:

1. Check VDD on the STM32 (pins 5 for analog power in, 16 for digitial power in).  I guess you should see 2.8V, 3.0V or 3.3V.  Ground is on pin 15.  Failure to see good power would probably implicate one of the parts above the micro.

2. Poke around the BT24296 chip.  While charging pin 4 (STAT) should go low (the designers helpfully pulled it high even though they don't appear to use it using the 3rd resistor above the cap on the lower right of the board).  Pin 3 (PG) should go low if the chip likes the battery voltage (2nd resistor above the cap).

3. Use your scope to probe the SW out signals (BQ24296 pins 19, 20) going to the inductor  at the bottom left to see if it's trying to provide power to the system - or you could measure across the two caps above the inductor (according to the spec sheet this should be 3.5-4.35V).

4. If the charger seems alive and the micro is getting power you could probe the I2C bus between the charger and micro (the 4th and 5th 10k resistors above the cap on the lower right).  This might show code is running on the micro.

If it's the BQ chip then that's an easy replacement.  If it's the micro then you're probably SOL.  It could also be one of the parts above the micro but I didn't really try to figure that circuitry out.  Other parts you could also probably replace although you'd have to do that dance where you figure out what part some small chip is based on the cryptic markings on top...

Would be curious what voltages the battery pack puts out and what communications it supports to the level.  Sure is a complex pack to just house a 3.7V battery (your two cells are wired in parallel).

[Shaky]

Well, all I can say is WOW ! Thanks for the comprehensive reply @globoy but unfortunately, it looks like repair is way above my pay grade 

All I have available to me is a mid-range digi multimeter, no scopes or anything like that. It was basically an attempt at trying to save a mate (who doesn't do anything electrical at all, let alone electronics) a few quid 

If it helps, the wall-wart outputs 5v, the battery is showing 3.6v but there is 0 volts on the + & - brass pins on the pack. Funnily enough, there is 3.6v between the - & the Y pin, which made me think it was just a simple charger/bms.

Ah well, I'll let him know that he'll have to wait for the packs to come back in stock.

Thanks again for the reply, it's appreciated.

[coromonadalix]

You could have a battery pack with "memory", meaning  they could show some voltage  but wont charge if everything is okay ...

Sometimes  companies use cheap packs or cell ...  if you can provide some 4volt  on the battery connector and everything powers up,  you'll know they are not good

and yes  with found parts dustsheets, STM32 mcu and the battery charger ic       you should be able to pinpoint where is your problem is / are  if there is, or the battery is not good

some rechargeable batteries do have some protection on one end,  when you unfoil the blue plastic,  some batteries may or could have an small pcb, and this pcb can open if there is a problem, it may act as a fuse / bms  ...

[Shaky]

You could have a battery pack with "memory", meaning  they could show some voltage  but wont charge if everything is okay ...

I didn't realise Li-ion suffered from the memory effect ! Thought that was just NiCd + NiMH, you learn summat new everyday - cheers.