Cordless drill battery charger

Impossible to be certain. However, bearing in mind it is a switch mode power supply and there is no obvious damage then I would suspect that the electrolytic capacitor that starts the supply has dried up. Do any of the capacitors look domed on top?

I would suspect the transformer.

There are many possible failure modes. The snag with troubleshooting SMPSUs is that if you don't change all the faulty parts, and there are often several, then the next time you switch it on for testing, the ones you replaced fail again. There are ways round this, such as with a lamp limiter, but fixing even a simple little supply like this can be fiddly and annoying, even with experience.

I personally don't suspect the reservoir capacitor or the transformer, as it has not had many power-on hours (caps are usually the first thing to fail in SMPSUs that are on 24/7 though). I can't see the power switching device but that, and the IC that drives it, the startup resistor (if fitted) and current-feedback parts are common causes of random failures.

I'd check for dry joints, check the DC output for shorts (which could be the output rectifier or reservoir) and any obviously vulnerable items such as current feedback resistor, other fusible resistors, startup circuit, output transistor and efficiency diode. If all looks OK I'd energise through a lamp limiter and isolating transformer to make sure there is 340V DC on the input reservoir that is reaching the transistor. OTOH if it's a monolithic IC, I'd pull it, test around it again e.g. up the opto-coupler for domino-effect faults, replace, then repeat from top.

Actually, no. I wouldn't bother, and I have loads of experience fixing SMPSUs. It probably isn't worth the agro.

For a few pence it's always worth a go (in my opinion) at changing the capacitor. Have repaired countless ones where it has dried out and has bad ESR. Usually they place them next to a heatsink as well for reasons best known to the designers!!

Sure, there's no harm in swapping the reservoir cap, it's not usually part of a domino failure chain so if it was bad, it might be the only bad part. I know what you mean about 'thermally undesirable' locations that electrolytics seem to find themselves in.

Buy a new one. They are dirt cheap

As Lucien mentioned check for dry joints also check the fuse in the plug top then see if you are getting power to the unit, I'd do this first.

i have twice found that it's the SCR (or transistor) failed. that's the bugger on the large alloy heatsink. about £1.50 from cpc. had this in a lithium charger and a washing machine.

The device on the heatsink looks bigger than a TO220 package so I suspect it might be an all-in-one PSU IC rather than a discrete transistor. It's a prime suspect, either way. I referred to it as the 'power switching device' for lack of clearer identity.

I'm still going to go with the small electrolytic being dried out. OP let us know if you do try anything and have any success!!

First thanks to everyone for the replies, didn`t expect that many, firstly I would have replaced it if I could find one, tried everywhere including Ebay. Not worth spending a lot, don`t know how long the batteries will last anyway. Had a look for similar drill/driver but being a tight old sod couldn`t find one at the right price, the Parkside ones were only £15 and like all their kit is good enough for a diy`er and got a 3 year warranty to boot. I`ve a friend who is a bit more savvy than me I`ll see if he can check the things mentioned.
Thought about a 3.6v screwdriver but no good for drilling, not enough torque, might have to bite the bullet and spend...…………….
If I get a result with the charger I`ll come back with what the problem was, thanks again.

Mr.C said:

First thanks to everyone for the replies, didn`t expect that many, firstly I would have replaced it if I could find one, tried everywhere including Ebay. Not worth spending a lot, don`t know how long the batteries will last anyway. Had a look for similar drill/driver but being a tight old sod couldn`t find one at the right price, the Parkside ones were only £15 and like all their kit is good enough for a diy`er and got a 3 year warranty to boot. I`ve a friend who is a bit more savvy than me I`ll see if he can check the things mentioned.
Thought about a 3.6v screwdriver but no good for drilling, not enough torque, might have to bite the bullet and spend...…………….
If I get a result with the charger I`ll come back with what the problem was, thanks again.

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Could this be the simple answer ?

aldi have a reasonable cordless and impact driver set for £99.95. 3 year warranty.

One of my Milwaukee chargers has just gone with a loud bang.
SMPS control chip has a hole in it, same thing failed in my other one. A replacement got that working again, so I have ordered a replacement IC for this one for £3. It's a tiny little thing for a power component.