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[barryfoote]

The charger for my 18volt electric drill has burned out. I got the tell tale smell. Now I have had a look at it and found that the long grey thingy and the little black thingy, shown in the third photo look a little blackened. As you can tell, I know nuffink of theses things.....Question.....Can it be repaired? or do I have to bin the lot?

If it can be what do I do......?????

[andrewh]

Footski,

Whatever they were, the components have probably been converted into SEDs.

That's Smoke Emitting Diodes, and is, as you guess, bad news

The news may not be terminal   the smell you got was the board overheating (phenolic resin - seldom a welcome smell)
The little black thingy is a diode, and the long grey thingy looks a bit like a power resistor.  both or either can be killed by heat, but the diode is the more likely candidate.

However there is some reason why they have let the smoke out.

I seem to remember that you are an expert wirth a multimeter
I have one of these - or at least a first cousin - and the wire that goes into the socket is believe about 24Vac (I will check tonight).
The transformer from mains power to low voltage is a seperate device, and plugs into this "stand"

Meter set on VAC, 200vrange - plug the charger together - no battery, and try the voltage at the metal charging points where the battery should connect.
Anything?  nothing?
go to DC voltage, 200VDC - do the same
Owt or Nowt?
If both give nothing, the charger stand has gone open-circuit

You could try (AC volts 200V range ) the output from the transformer at the end of the lead it should be around 22 to 27 Volts AC (not dangerous)

The "stand" is a simple and not clever device which rectifies (turns AC into DC) and feeds it into the battery (the current is probably roughly set by the resistor)
If you can find which bit has gone kerblooie we can prolly help you fix this at a distance
andrew

[stallspeed]

It looks fixable.
Can you read the coloured bands on the grey resistor and give dimensions?
You have a separate power supply? Got the spec? Is it OK or states that it is overload protected?

[barryfoote]

Thanks for the quick response guys.

As I am obviously NOT a multimeter king, I have a problem......My multimeter is out of action due to a blown fuse and I considered it safer not to replace it as it has given no problem since!!!

The transformer is a seperate devise and has a label stating CE......It is an AC-DC charger, 230v~50hz 15W, 25v----400mA 10VA

All of this is Chinese to me

As for reading the bands on the resistor, there is no writing visible on it, but then it looks a little powdery The bands are coloured orange, brown, gold and brown.

[stallspeed]

The grey component was probably a fusible 3.3 ohm resistor based upon the info here http://www.elexp.com/t_resist.htm Possibly started orange/orange/gold/brown.

You can still get volt/ohms and diode test measurements without the fuse.The fuse is in series with the red probe when the meter is in the 0.2 amp range and RED is in the amp socket.
Probing the diode at the -I>I- setting ,the diode should read ~0.5 one way and over range with the probes reversed.The resistor should read 3.3 to 4 on 200 ohm range.
You can replace both for pennies anyway.
I was cautious about the using an abused power supply but it should be OK
Good Luck

[malcolmfrary]

The bits of the board with the best suntan appear to be under the black tube (diode), probably a 1N4001.  The replacement is pennies (a 1N4005 is a higher current more or less the same size replacement)  - just note the end with the silver band and make sure its replacement goes in the same way round.  The heat could also have been generated by the resistor and passed into the board via the wire leg - usually a dead resistor will have a black and crispy appearance, or at least a noticeable discolouration.  It is likely a 1 watt one, if I could find a higher wattage replacement that would fit in the same place, I would use that instead, the price difference being, again, pennies. Resistors don't care which way round they are fitted.

[barryfoote]

Thanks guys very much. I will pay a visit to my local electronics shop tomorrow and report back..

Barry

[barryfoote]

The grey component was probably a fusible 3.3 ohm resistor based upon the info here http://www.elexp.com/t_resist.htm Possibly started orange/orange/gold/brown.

You can still get volt/ohms and diode test measurements without the fuse.The fuse is in series with the red probe when the meter is in the 0.2 amp range and RED is in the amp socket.
Probing the diode at the -I>I- setting ,the diode should read ~0.5 one way and over range with the probes reversed.The resistor should read 3.3 to 4 on 200 ohm range.
You can replace both for pennies anyway.
I was cautious about the using an abused power supply but it should be OK
Good Luck

I have done as you say and do get the approximate readings you mention. Does that mean these components are okay?

[barryfoote]

Re the above, I meant reading on the diode and resistor. I have also plugged the power supply into the mains, the stand into the power supply and tested the voltage with the multimeter set to 20 V. I get a reading of 0.03. Totally confused now!!

Barry

[malcolmfrary]

In that case, the components around the darkened board are OK and the problem is deeper inside.  At this stage I would seriously consider mending it with a new one. 

[Tug-Kenny RIP]

 
Sorry to inform you, Barry, but the mains transformer is burnt out. 

ken

[barryfoote]

Thanks guys......At least you have saved me a trip to the electrical shop.....Now anybody fancy buying me a new one for my birthday?????

[Guy Bagley]

footski do you have and other chargers? , i have several one of which allows me to select output voltages/ number of cells- it was not a cheap bit of kit but it does allow me to trickle charge  battery packs upto 24 volts, i never thought of it until now but it would charge my drill pack if needed too
 on a trickle charge basis
thinking laterally if you do  see if they will allow you to charge your drill battery, 18 volts, but charge it slowly ....

[stallspeed]

I think this is what Guy means.They are universal d.c. psu of the type used for lcd monitors and laptop pcs.....brill things.regulated,overload protected & versatile
http://computers.shop.ebay.co.uk/items/Universal__W0QQ_armrsZ1QQ_mdoZComputingQQ_msppZQQ_pcatsZ101262Q2c42168Q2c31530Q2c58058QQ_sacatZ64471
If the link does not work then you can navigate through Ebay to see what I mean.
Home >Buy >Computing >Laptop Accessories >Power Supplies >Standard/ AC Power Supplies >Universal

"the tell tale smell"  ?........It is normal to have scorching on a resin bonded paper around a 1 amp diode but I  would two further tests before junking a supply.

I don't know if your measurement was ac or dc volts but two (sometimes fixable) faults give funny voltage readings:-
A broken wire or solder joint OR
A thermal fuse activation changes the resistance across the Live-Neutral pins from kilo-ohm to open circuit.That device looks like either of the two pictures and is either glued to or buried(beyond repair) in a transformer 230 volt winding.

That's another 50p and it takes care to solder them in.
It's up to you if you confirm something has gone and worth your time to fix.

[Proteus]

I use a chock/Terminal block with  thermal fuses  , don't have to worry about heat then

Proteus

[barryfoote]

I do have a charger for my SLA's, varying voltages up to 12. It has crockodile connectors. may give that a go on the battery..

As for those little things pictured above, I cant find anything that looks remorely like them!!

[stallspeed]

Remove mains plug and do a resistance test with a meter on 1,000 kilohm or 1Mohm across the live & neutral.

If a thermal fuse has blown it reads open.If it is intact you get a reading of 10k to 1000k.
That is the weakest point of an approved consumer transformer.If that fuse has not ruptured then I think the likelyhood of a blown transformer is low.
I've got just a few hours of transformer design & test under my belt.It's rarely useful in the real world.

If you get an open circuit reading :-
A thermal fuse,if not buried inside, is glued adjacent to the thin copper windings and under polyester tape.
It is easier to trace by its solder connections to a circuit board where it is in series with the winding.

[malcolmfrary]

Following from stallspeed, you can check the other side (output) of the transformer by plugging the transformer into the stand, and testing across the red and black wires as in picture #2 for a resistance reading.  It should be maybe a few ohms.  If the transformer is working, when plugged into the mains, the meter should show about 24 volts on the AC volts scale connected across the red and black.
Most cheapo battery eliminators stop at 12 volts DC, even attacking them to make them AC out will only give 16 volts, not enough.  If you find a "left over" plug top transformer from a printer that doesn't work any more, you have a suitable source. Unfortunately, higher voltages tend to be for "equipment" rather than general use, so are not as readily available.
It seems reasonable that the crude current regulation might have regulated a bit high for either the transformer itself or the "regulating" circuit.  Almost as close to the limits as the old Hitec gold brick ESC.

[stallspeed]

From Footski's earlier post I think the psu is dc so it contains another four diodes and capacitors and his red/back will not be to the transformer.
Open circuit across either transformer winding means it is unservicable.A visual check can exclude a broken track or solder joint.

It seems reasonable that the crude current regulation might have regulated a bit high for either the transformer itself or the "regulating" circuit.

Before you try probing with the thing powered up there is a last gasp test......the same diode test applied to each diode of the ac to dc bridge rectifier(see picture attachments)

[barryfoote]

Thanks guys,

Tested the charger as suggested and no reading found......Final decision made........The damned thing is now in the bin......I have just spotted a "Thork" 18 volt drill with charger and two batteries, plus accessories for 41 euros in a local supermarket, so may give this a look..

Thanks for all your advise...