Bionx Battery problem

[izzzzzz6]

Now i'm a little confused. It appears this is not a 5MO resistor but a very low value current sensing resistor. Are these designed to go short? Removing it removed the short across the charging power input but if this is correct it is supposed to be almost dead short.

 

[amberwolf]

Well, that's a five milliohm resistor, probably used as a current-sensing shunt. Unless you have a multimeter designed for reading such low resistance, it'll appear as a virtual short across it.

If it helps, there are a number of sites you can use to try checking SMD component values based on their markings; a google search on the marking may find them too.

This one works for resistor marking codes, for instance:
https://www.hobby-hour.com/electronics/smdcalc.php

So this is an old thread but i'm wondering if anyone has repaired the 48V bionx charging board (looks like the one in the photo above but it's the SMC 6.3 version).
I wanted to see if it would charge at 25V rather than the normal 26V but the current must have gone high and now there is a short across the charging input cables.
At first i thought it was D2 but now wondering if the 5MO resistor might have gone short? Also there are flat metalic smd transistors that look seriously difficult to remove. Not easy probing around here without a schematic.
Any tips?
I'm going to probe around a bit more but i might resort to putting some power through and see what gets hot.
I'm editing the message, i went straight to remove the 5MO resistor, on the version 6.3 it is on the back of the board. Here is a photo. It is reading short and i'm assuming it should be 5Mohms. I'll have to see what i have in the way of standard resistors, not sure what the power rating of this is but it's quite big for an smd, you can see the same part in the photo posted above but it's on the front side in that photo.IMG_1845.JPG
Now i just need to work out which way around D2 was and see if anything else is shorted.

 

[amberwolf]

It removed the short across the input because it removed the path for current to get anywhere past that point.

There is something else beyond that resistor in the circuit that is causing the short. I don't know what the specific circuit is in side there, so you'd have to trace it out to see where it goes.

Keep in mind that if you are measuring resistance across a battery input port, you won't read a real resistance with a regular multimeter because there is a voltage present on it from the battery.

If that's not how you are measuring, you'll need to show / state exactly what you are measuring and how, and where, so we can help you figure out what the problem might be.

If you're measuring at the input to a separate board, without the battery attached to it at all, then that should show a real resistance, but we still have to determine the circuit to see what might have failed.

The most common parts that fail short circuit are capacitors (elecrolytic or tantalum), reverse-connection-protection diodes wired directly across an input port (as opposed to those placed in series with one input wire, which won't cause a short across the input), and switching circuits made with FETs (but they are not normally on the *input* side).

Now i'm a little confused. It appears this is not a 5MO resistor but a very low value current sensing resistor. Are these designed to go short? Removing it removed the short across the charging power input but if this is correct it is supposed to be almost dead short.
Screen Shot 2022-06-13 at 19.38.26.png

 

[izzzzzz6]

Thanks for the speedy reply!

Well, i have some updates.

There is no power on the board as i removed the fuse and i am working around the power input zone.

I saw that the short was deeper in, but, not that deep!

I decided to remove the 4 transistors in that zone IRF6668

2 of them were short and two were fine.

I'll order some from Ali but re-soldering these is going to test my skills!

Now i need a glass of wine! & a vape.

 

[izzzzzz6]

BATTERY BOARD REPAIRED

I had the repair job sitting on the shelf since the last post.
It was not easy soldering these transistors since the legs are hidden, my hot air setup is not great and i'm not sure hot air would have done the job anyway due to the metal can design. Careful board preheating would have been crucial in order to have a hot air station do the job.
Here is how i did it. Sorry i did not take photos but the finished job looks the same as the original but without 100% perfect alignment.

Tools were standard rosin flux, high quality leaded solder (HX-T100 0.3mm), mid grade solder station set to 380C medium fine tip. Solder braid and tweezers.

Obviously clean up the area on the board with flux and solder braid then tin the pads with very small blobs of solder.
Tin the transistor pads but i didn't tin the can edges ( the can is one of the transistor switching legs, the gate is the small pad on it's own below the 2 pads which are joined together electrically).

Once all of the tinning is finished here comes the difficult part. Place and solder the transistors one at a time into position. there are white screen printed lines to show the lateral position on the circuit board. For the end to end position you just need to even out the position of the solder pads for the can.

You need patience, skills and a steady hand for the next part. Take a strip of used / saturated solder wick and bend it so you can hold it in the tweezers and lay a flat section over the middle of the metal can of the transistor. use some flux also. Then place the iron onto the wick, sandwiching the solder saturated wick between the tip and the can. This helps to spread the heat quickly throughout the device and the transistor will soon start to float around. The hard part is to get the transistor in the correct position as you lift the wick away.

This took me several attempts. The first attempt was without the solder wick as a heat transfer tool and the transistor separated exactly like the one in the picture above. It was very fiddly and once i had finally finished i thought that one of them may have been too much out of alignment, it wasn't. They don't have to be 100% perfect but they do have to be very close.

I also thought that by the time i had adjusted the position several times that my solder would be bridging and the transistors wrecked but i must have done ok because everything tested ok and worked. You can check the soldering by using diode mode on your tester and checking between the casing of the transistor and either side of the capacitor next to that transistor. You should get similar readings for each one. I think on diode mode i was getting approx 600 on one side of the cap and 1.900 on the other side. No idea what that means other than the diode in the transistor and something else going on to the other side of the cap.

Still apprehensive i put everything back together. initially i got the charging noise and the orange light but then a red light with a beep. however on 2nd time connecting i never got the red light.

I found that after the board has been disconnected this red light showing once seems to be a thing. i also remember this happening after leaving my bike in the shed all winter. Seems to be a thing after lack of use the 1st time you try to charge / connect the board. I'll update if this turns out not to be the case.

So, that's it! The battery fully charged. One other thing i was worried about was the spade connectors that connect to the board. I found it extremely difficult to remove them, there seemed to be no access to inset a tool to unlock them so i had to use force with a twisting gyrating motion. As i was doing this i could hear cracking noises coming from parts of the board. I was worried that dry solder joints may have formed from this flexing, however everything seems fine. I am yet to test the repair on the bike so, i'm a little concerned about how the regen charging may go. If anything breaks i'll keep y'all posted.

Do not try to charge at below 26V !