Aldi 12V Battery Charger Repair - where to start ?

[Shaky]

Hi all, first post so be gentle with me .

I've had an Aldi Workzone 12V drill for about 4 years and it's worked fine up until a couple of weeks ago when the battery charger appeared to fail. I'd put a battery in it to charge, the red LED lit to show it was charging and I let it do it's job. When I returned to it later (admittedly about 5-6 hours later but I believe it auto-stops ?) no LED's were lit at all and when I tried the battery (which was just too low on charge to be of much use when I tried to charge it) there was absolutely no charge in it whatsoever. I tried the plug fuse, which was fine so thought seeing as it was out of the 3 year warranty, I'd have to buy another one

Unfortunately, they are no longer available . This wouldn't be quite so bad if it wasn't for the fact that I bought a couple of spare batteries for it a year or so ago which are still OK and the actual drill itself is still performing perfectly .

So, the question is, would it be possible to repair and if so, could any of you guys point me to how to do the testing required to try to narrow down the fault ?

Looking at another post on here by someone a while ago, they were asked to provide a piccie of the PCB to help so I've attached one:-



My knowledge of testing of components is very limited. I know the ballistic test for a capacitor and how diodes should only show continuity one way but that's about it I'm afraid. I've tested for 240V either side of the fuse (FS1) and if it's present on one leg of the large yellow capacitor bottom left and it was present there also. Nothing on the other leg though. Neither of the electrolytics appear to have any scarring or bulging either and I can't see any burn marks anywhere else. Piccie of solder side here if it helps:-



I have an analogue (needle type) meter and a digital type and understand basic testing principles and can solder proficiently so replacing any faulty components shouldn't be too taxing.

TIA

 

[Martaine2005]

Hi and welcome to EP.
First, if you know how to check diodes, you could start with the four diodes bottom right in your first photo.

Martin

 

[Shaky]

Cheers Martin. I'll have a go at that first thing tomorrow

 

[Shaky]

All diodes checked this morning, all four test OK, between .75V & .766V in forward bias, open cct in reverse.

 

[Martaine2005]

Good morning,
Can you check the voltage directly across the yellow cap, making sure there is indeed line voltage.
Next would be to test the NTC. If it’s open, that’s the problem. It should drop in resistance as you heat it (tip of soldering iron or hair dryer etc). Place your meter across it while heating.

Martin

 

[Shaky]

Hi Martin. Firstly, I really appreciate this, thanks for taking the time out to give me the run-through for checking.

Full line voltage is present across the big yellow cap. The NTC registered 29.8Ω at prevailing temperature and just breathing on it made it drop to 22.6 so I presume that is OK also ?

Hopefully something will actually show up as faulty eventually or maybe I'll just have to junk it

 

[Martaine2005]

My next check would be the transistor (switching transistor) on the heat sink.
You should take this out of circuit to test it. Also you’ll need to check online it’s part number for correct pin out.
Some members would be able to tell you straight away but I cannot.
Don’t dump it, hopefully you’ll get there. It’s a process of elimination with just a multimeter on hand. And SMPS are quite complex.
Never fear, plenty of experienced techs here who will chime in too.

Martin

 

[Shaky]

Oh I won't give up just yet Martin. I hate the "throw away" society we've become. Thanks to forums like this, there's usually a way to repair stuff and long as you're willing to get "stuck in" so to speak.

I'll get my soldering kit out and start to disassemble then. Will reply with my findings

 

[Martaine2005]

I just noticed something on the underside of the PCB.
Top right of the 8 pin IC, upper most capacitor C13. It looks like one side has blown? Can you confirm this?

Martin

 

[Bluejets]

A knackered battery could well be the only problem.
Did you try a known good battery....???

 

[Shaky]

My next check would be the transistor (switching transistor) on the heat sink.

Hi Martin, have done that and it appears to be working OK. It's a SVF5N60F unit, found the pinout and have used youtube to see how to test it. The results were:- no continuity between - on source and + on drain until I turned it on by putting the + on the gate. I then got about 550mV or so as it allowed current to pass. I did notice a couple of times after turning it off (by shorting the gate and source) that if I put the - on the source and the + on the drain, there was a momentary current flow that then returned to an o/c result but that only happened a couple of times - signs of it going duff or not ?

I just noticed something on the underside of the PCB.
Top right of the 8 pin IC, upper most capacitor C13. It looks like one side has blown? Can you confirm this ?

Tbh Martin, I wouldn't know a blown SMD from a good one - lol but I do see where you are coming from as it definitely looks different one side to the other. I've tried to get a better piccie here to see if it helps:-



If that's one of the issues, that'll be fun for my 56 year old eyes to sort out - hah !

A knackered battery could well be the only problem.
Did you try a known good battery....???

Hi Bluejets, thanks and yes, I did try the other two good, working batteries but still no joy. When the charger was working OK, even without a battery in it, the red LED would light but there's nothing at all since it went.

 

[Martaine2005]

You’re doing really well.
Sometimes, capacitively touched transistors will change state and yours sounds fine.
The next obvious things to check are the diodes either side of that high frequency transformer. Four in total. You could also check that resistor by the transistor.
The cap on the underneath looks ok and is probably just lots of flux.

Martin

 

[Shaky]

Hmmm......Interesting. The two small ones (D2 & D3) give readings of 632 & 727mV forward and o/c reverse which I guess is OK ? However the larger ones (D14 & D15) give readings of .01 forward and reverse on the diode test of my dmm which to me sounds like a s/c ?

Maybe I should desolder one leg incase the pcb has a cct path elsewhere ?

The resistor you mention is yellow purple silver gold. Am I understanding the codes wrong coz I make that 4,7,.01 multiplier and 20% tolerance but I'm getting 3.9 ohm.

 

[Shaky]

Update.....just dissed-off the D14 & D15 diodes. D15 tok 472mV forward, o/c reverse. However, D14 looks s/c both ways so definitely looks like 1 flty component found ?

 

[Martaine2005]

Definitely seems to be a short on that diode.
I was going to say lift a leg on each to test out of circuit but you beat me to it.
That resistor comes back as 0.47Ω 5%. At least on my chart. Probably the sense resistor.
Edit: you’ll probably need to lift a leg on the resistor too.

Martin

 

[Shaky]

Cheers Martin. Yeah I lifted a leg on that resistor and got less than 1ohm (cheap dmm so not expecting fantastic accuracy - lol.

The diode is an SB5100 which apparently is a Schottky Diode ?

So the crux of the issue is, do you think that diode going s/c could be the root of the problem or are there likely to be other components damaged as well requiring further testing ?

And, is there anywhere where I can purchase any of the components required in small quantities that don't want eleventy-million quid for p&p .

Thanks again.

 

[Shaky]

Looks like eBay is the best bet, less than a couple of quid for the diodes.

 

[Martaine2005]

Well done, yeah eBay seems cheapest. That resistor seems fine too.
I can’t really compare both sides of the board on my phone so it’s hard to say for sure. Give me a few hours as I’m cooking a BIR curry as well lol. I’ll try and see if I can trace where that diode goes. Normally I would suspect the transistor if the diode has shorted but you’ve checked that and it’s fine. Personally I’d put a diode in and try it. I think we’ll have to flip the board over and check voltages on the charger IC if it still doesn’t work. But let’s hope not. In the meantime, you could look up that chip and see what it is.

Martin

 

[Shaky]

Hmmm curry had to put up with sos, egg and chips tonight but our lass is doing a lamb roast tomorrow .

I'll get some diodes ordered anyway coz not too expensive.

Cheers again.

 

[Shaky]

Well, looks like it was maybe not meant to be - lol. Took apart an old PVR unit I found in a cupboard and yes ! it had SB5100 diodes in it. So took one out, tested fine and put it in the aldi charger. Put the mosfet back in and tried it with a good battery that was about 50% charged. Red LED lit up to show it was charging - yay, thought it was done........10 secs later, green LED lit to show full charge - eh ?

Looks like it's gone again and in the process, took another battery out which now can't be used - lol. There's circuitry in the battery that stops you being able to use it when the charge gets too low so I can only presume that's been taken out by the faulty charger - sigh.

Best bit is that this time it's blown the fuse in the plug but not the one on the board so I had a poke around with the meter on continuity and found that the heatsink on the mosfet was now in contact with the live mains in ! I can only think I've screwed-up somewhere (even though I can't see anything) with my resoldering - lol.

Still it gave me summat to do today

Thanks for all your help Martin - sorry to waste your time. Hope you enjoyed ya curry