Ansmann Energy 16 PSU

I would take those out and check outside the circuit.

If the short is at the output of the bridge rectifier, and all four diodes are good, you should measure a diode drop (0.6 V or so) across the diodes in both directions.

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RoRo

Replace the shorted recctifiers!!!! As a precaution, replace all 4 of them; they're cheap. Even in circuit, they should not test as a short corcuit.

Cheers, Dave M

T i m wrote:

if you test individually: 0.6v one way only if testing at bridge input: 1.2v both ways

An easy way to find faults is to run the psu via a filament light bulb, then it's easy to probe the [dangerously live] circuit for voltages with due care. Since I don't know if you can do this safely, don't do it.

NT

Thanks Robert / Dave,

I haven't played much with SMPS (for obvious (safety) reasons) so assumed there might be some strange 'appears short but isn't in use' type thing going on. I should have pulled those diodes before asking here. ;-(

However, I just desoldered one end of both and one appears to be dead short but the other was ok (but I've pulled them all).

Problem is, while I probably have 1,000 IN4004's, I don't have any

1N4007's and I'm guessing we need the 1000V peak reverse / DC blocking voltage (rather than just 400) and 700 over 280V RMS? ;-(

So, I can pick some of those up next week (eBay) or it looks like Maplin have 1N4007S's in stock but are they an acceptable equivalent? (Peak forward surge current, 30 not 50A)?

Cheers, T i m

p.s. How long is a piece of string question but ... Is it 'likely' that diode just went (the charger is a good few years old now and has been used quite a bit), or is it more likely something further down the line took it out?

Yeah, my diode test function was showing around 520mV on the good ones.

Understood.

I did remember that earlier and was going to rig up a plug - lamp

-socket jig to make it easier. I thought I'd better ask here first. ;-)

Understood.

Understood. Whilst I have co-designed and scratch built plenty of mains powered kit (including disco sound-to-light, sequencers and strobes) I prefer not to be playing with live kit unless it's the only way (or the kit is very well mounted and otherwise insulated / protected, not just loose on the bench etc).

Cheers, T i m

It is likely that the off line switch regulator is also failed. Grab a copy of the TOP223Y datasheet to see the reference design for your supply.

Here is a source for those chips:

Yes, the 1N4007 recrifiers should be good replacements. Likely to be the only problem in your unit.

As a precaution, you should check the large transistors on the board. They are likely to be high voltage MOSFETs, and should NOT be shorted or low resistance from drain to source or from gate to any other terminal. Best to take them off the board to test, since they're certain to be connected to the low resistance transformer windings, which could lead you astray.

Cheers, Dave M

T i m wrote:

Dave,

The "large transistors" are TOP223Y off line switching regulator ICs. Google the part number for the datasheet and reference design.

Regards

There are two in this PSU so could that apply to one or both?

I have looked at this:

... and see roughly how it would work but not sure if that means I should be able to test it somehow? FWIW, I have one of the little component testers but I don't know if it will know what that is or even damage it?

Thanks for that. However I am in the UK and but get them here also. ;-)

Cheers, T i m

Would you think one of those component testers would be able to identify the PWM reg, at least with a go/no-go result?

From testing around there were no shorts around the devices but that doesn't stop them being OC or just non-functional?

Cheers, T i m

A quick ohmmeter check across the three pins should not show a short circuit.

If it does so in circuit, you may need to remove the device to check.

Look at fig 8 in the datasheet for how your unit works. If I read your post right, this charges LiIon batteries, right? So the outputs should be about

4.0 to 4.2 volts. There is some feedback coming from the battery that probably looks at the battery temperature for a safety shutdown.

You could probably reverse engineer the whole schematic (or half of it) to get a better view of what is going on.

BTW, the transformer on the right next to the capacitor is not a transformer. It is a common mode choke for RFI filtering.

OK. Again, I get the rough idea but I was more into digital electronics than SMPSU etc.

Sorry, no, it's a general purpose multi-cell NiCad / NiMh charger Tom.

The PSU board feeds a fairly complex logic / output board (4 PSU outputs to the logic board) and in turn the 16 charger outputs.

Ok.

Ah, ok, thanks ... that (now) makes more sense as even with that (choke) in and D1-4 out, I've lost the short I was seeing across the mains input. ;-)

Cheers, T i m

Ok, good. That makes more sense for why so many outputs.

Doing any measurements on this device (scope, etc) will require an isolation transformer to look at the primary (line) side. The outputs all appear to be isolated.

Hope it's just the shorted diodes.

Good luck.

Regards

I've been led astray by small amounts of capacitance before

NT

It's quite an expensive unit (I think it cost me ~100 UKP some years ago) so I'd like to get it going if I can.

Understood.

Ok.

Fingers crossed. ;-)

Thanks for your help and I'll let you know how I get on.

Cheers, T i m

you would, 99% of the time

if it's only 1 bad diode try running it without it, on half load or less it should be ok. 2x400v diodes in series should do as replacements temporarily.

NT

Now I've got them all out it seems to be two bad diodes but one was reading strange things so maybe died fully as I got it out?

Ok, I can give that a go tomorrow ... especially as I have so many

1N4004's. ;-)

Cheers, T i m

Unless the output is shorted.

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RoRo