trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

[Tarot Superstars]

Hi. I am trying to fix a 6V 5A power supply that would was used a lot.
I want to fix it partly for learning, and part because I don't want to buy a new one.

It has distinctive smell of burning but not seen obvious burned components yet. I'm not sure where the fuse is.
I tested the only slightly bulged capactitor (out of circuit) and it measured normal capacitance and ESR.
Everything else was tested in circuit with a multimeter.

In circuit tests
I tested the large diodes underside and they seem fine.

I tested the transformer in circuit for continuity and resistance using a multimeter, but not sure the readings are correct because other circuitry is nearby.

primary pins 1 and 2 showed resistance and continuity in circuit.
secondary pins 3 and 4 showed resistance and continuity in circuit.
secondary pins 5 and 6 showed resistance and continuity in circuit.

But secondary pin 3 to 6, 3 to 5; 6 to 3 and 6 to 4 showed no continuity.

I watched a video about testing transformers out of circuit and it showed
continuity from one of the outer pins to all the other 3 like they
were tapped on a coil.

I am not sure the tranformer is working but I am hesitant to believe
it's blown since some people online say tranformer's don't burn out much.

I have not tested the surface mount components apart from the large diodes.

I have attached some images with component values and notes in the .pdf.

Does anyone have an idea how I should approach this repair? Any common faults of this? Any advice is appreciated.

[H2814D]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

The most common failure points on those power supplies, are failing/failed electrolytic capacitors. If the unit has been in use for a long time, like you say, and there was nothing else that would have caused it to fail, like a power surge of some type, I would check each one of those caps out of circuit. You said you tested one out of circuit and got an ESR Reading, so I am guessing you have an ESR Meter of some type. Have you tested the others in circuit with that meter? In-circuit testing of e-caps for farad value, is not reliable. They have to be removed. At least one leg anyway. Not so with an ESR Meter.

You say there was a "bulging" one that tested fine. If it is bulging, it needs to be replaced no matter how it tests out.

Those caps are cheap. I only see five total. Order new ones of each and replace them all while you are in there. My bet is on the two green ones at the output.

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Thank you.
It looked like it was bulging compared to the other. But I think it was just the crease and the angle I was looking at it. I have seen bulged capacitors before and this doesn't match those.
It was either C1 or C2. They have the same value.

I only tested that one out of circuit with a cheap component tester (LCR 4T).
The measured capacitance matched the label (~4.7 uF) and it was about 4.5 Ohms ESR. The ESR table says highest ESR for that is around 5 Ohms for a 400V. That's why I thought it was ok.

I will test all of the capacitors out of circuit next time I do some practical work on it. I think I will do that before testing the other parts in circuit.

I think I will go and test everything in circuit when I get the chance. And maybe try to find a short using a milli ohm meter.

[Tarot Superstars]

trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Hi. I have replaced all of the electrolytic capacitors but it doesn't work. I haven't tested any voltages yet.
There is a smell like a burned semi-conductor.

There is an IC on the underside but I cannot find a datasheet form the number.
The adaptor is a UK AC to 6V 0.5 A adaptor.

The IC has 5 wires, and the top marking is:
0S429. I think the last digit is 9.
On the other side of the board is a mosfet: 1N65T 1424.
I assume the IC is controlling it.


I have attached close ups.

Can anyone tell me where I can get a data sheet and where to buy a new one?

[Tarot Superstars]

trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Correction, I think the IC marking is OS429 starting with the letter O, because most components start with 2 letters. I could be wrong.

[R_J]

trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Did you check the resistance of F1 resistor? looks like a 10Ω 1w, Have you checked that the output leads are not shorted or broken (open)

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Hi.
I just checked F1 and MOV1 out of circuit.
F1 is supposed to be 1W 10R and it measures open circuit and 0 Ohms.
MOV1 is colour code brown, black, violet, silver, I assume 100 Mega Ohms and it measures continuity and 14 Ohms.

However, just previous to that, I tested the voltages of the primary and secondary windings with the power on, and made a small spark when one of the probes shorted on the primary underside with maybe a SMD resistor. I am not sure if this caused F1 and MOV1 to break.

When I measured the transformer windings, They measured primary 9R 0V, 4.7 R 0V, secondary 4.2 R 0V.

Also I have changed all of the electrolytic capacitors.
Not sure where to get a replacement MOV1 since Ebay only seems to do resistors.

PS: I was wearing an insulated jacket, rubber gloves, and protective goggles, so no danger of a shock.

Any advice is appreciated.

[sam_sam_sam]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

What I will sometimes when working on primary of a switching power supply and the traces are very small and very close to each other

I will sometimes solder very thin wire to where I want to check the voltage so I do not slip with the meter leads that just what I do sometimes

I hope this helps in the future

[R_J]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Hi.
I just checked F1 and MOV1 out of circuit.
F1 is supposed to be 1W 10R and it measures open circuit and 0 Ohms.
MOV1 is colour code brown, black, violet, silver, I assume 100 Mega Ohms and it measures continuity and 14 Ohms.

However, just previous to that, I tested the voltages of the primary and secondary windings with the power on, and made a small spark when one of the probes shorted on the primary underside with maybe a SMD resistor. I am not sure if this caused F1 and MOV1 to break.

When I measured the transformer windings, They measured primary 9R 0V, 4.7 R 0V, secondary 4.2 R 0V.

Also I have changed all of the electrolytic capacitors.
Not sure where to get a replacement MOV1 since Ebay only seems to do resistors.

PS: I was wearing an insulated jacket, rubber gloves, and protective goggles, so no danger of a shock.

Any advice is appreciated.

I see two holes for the MOV1 but I don't see it in place, are you sure you are looking at the correct component? That component is likely a coil
It is likely going to be more time and money to repair this than it is worth

[harp]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Does anyone have an idea how I should approach this repair? Any common faults of this? Any advice is appreciated.

NHF, but I dont get it what is purpose of pdf content, many questions, notes about nothing and you have big effort on that, but it is confusing if you feel ready to that repair? I do not understand your approach to repair psu, and not clear what is the base of your knowledge... but ok...


I assume that you know how to do measurement, in which mode and all needed precaution.

So, look "D6" and near D? (on your sketch D5 and D4 THT) in diode mode, what is voltage drop?
Also check again resistance of "F1", it is not clear what you mean "it measures open circuit and 0 Ohms"... and check resistance of inductor L1 (big green THT) and L3 (little SMD).

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Hello.
I have a BSc physics, The F1 resistor is supposed to read 10 ohms. The DMM on continuity is no beep. On 200 ohms setting it read 0 ohms.
I wrote the pdf in a few minutes. It was a skill I got from doing my degree.
I understand basic component testing and repair. I am not an engineer. Though I have read books on electronics... I consider myself a beginner.
So, the point in the pdf is that's the kind of thing I do to keep notes and transmit information properly. You don't need to read it. It's just for people who want to know every detail.
The purpose of the repair is learning. I have a replacement.

Edit: I wrote the pdf to keep notes of my progress and to help me learn. It saved time to just post it here than repeat everything I did.
I have some books on electrical fault finding, including one of the C&G that includes basic fault finding. I am ready to do the repair.
I completed a video course on Youtube Learn Electronics Repair Beginners playlist, about 25 h long.

I was studying electronics before Uni but had to stop, but finished my degree recently and went back to studying electronics. I like electronics and I do it for fun and learning.

I have made more notes and test since but did not put them here. I already tested the diodes D6. It's two in series labelled SR2 maybe something else. I think they are to stop high voltage either way during AC current. They measured ~ 0.7V either way since they are anode to cathode. I measured them in circuit. I probably should test them out of circuit too.

Surely F1 is broken and MOV1 is much less resistance than it should be.

L1 has continuity but haven't measured the resistance on that or L3 yet.

So, far this adaptor seems to have more than one issue and not simple. I have ordered new F1 MOV1 replacements.

[harp]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

The F1 resistor is supposed to read 10 ohms. The DMM on continuity is no beep. On 200 ohms setting it read 0 ohms.

The F1 have one end open to main socket, so you can not trust your multimeter anymore if it measure 0 ohms and not beeping.

When you test such small device who work with mains, use a 60w bulb in series like current limiter when connecting it in mains. That prevent some major damage, mistakes, and inform you in real time.

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Thanks for the advice about the limiter.

I removed 1 wire of the F1 resistor and tested it using a RS Beckman T100B multi meter which I know is working fine. It is 10 * more reliable than the cheap meters people are buying from ebay.

If the multi meter doesn't beep when in parallel with resistor, this means the resistor is open circuit and doesn't work. If the colour code says 10 Ohms then this meter should be able to read it. If it measures 0 Ohms when on the 200 ohms setting, this should confirm that the resistor is open circuit.

Also, when measuring resistance I do not connect the adaptor since that is the way that was recommended. As far as I know, resistance should be measured with no power.

Are you saying I am measuring it incorrectly or that my method of measuring is incorrect?

[harp]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

If it measures 0 Ohms when on the 200 ohms setting, this should confirm that the resistor is open circuit.

0 (zero) ohms mean no resistance at all, it is like bare wire, so it is reffered as short circuit.
Open circuit have "infinite" resistance. Check this issue before moving on.
Your conclusion is incorrect, how you confirm short circuit then, and how to distinct it from "0 ohms open circuit"?

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

The resistor is open circuit. I would appreciate it if you stop picking at hairs. If you don't have anything helpful to say, then could you just let someone else speak?

There is nothing wrong with my education, my documentation, my multtimeter or my understanding of short and open circuit.

I will not be replying to any more of your posts Harp since you are either trolling or something I don't want to say. The fact you are a senior member does not entitle you to troll on my thread.

[stj]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

the fuseable resistor is open circuit - so you have a short on the primary side.
usually the rectifier or mosfet circuits.
you dont have a mov fitted - if you did it wouldnt have coloured stripes anyway.
your mistaking an inductor for a mov.

and you didnt upload pictures - people dont want an ebook or a youtube video - just jpegs.

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

I just hope it isn't the IC, since I don't know where to get that.
Do you mean the diodes in the bridge rectifier?

The legend says it's MOV1 and the component has colour code brown, black, violet, silver. There are Jpeg's I attached. I checked and there is no other legend near that component.

I have changed things since then. The large cap on the left was one I replaced and the one next to it has now been replaced too. 4.7 uF 400V.
In the 3rd photo, the bridge rectifier is on the underside, left hand side.
In the 1st photo, there are two diodes on the top rhs and they are in series cathode to anode.

I measured the mosfet on the top side in circuit and could see the junctions of BCE and they measured ok in circuit, with BC ~ 0.5V and BE ~0.7V, but from watching videos, it could fail at higher temperatures.
The mosfet is Q1 3 wires 1N65T 1424 1.2A, 650V n-channel power mosfet.

Are you sure that I mistook an inductor for an MOV?
It looks like there is legend for a MOV but it's not fitted. I don't suppose it would be on the underside.
Ok, I checked again, the L1 legend is under the inductor wire. So, yes, it's an inductor. It measured 14R when set on 200 R and I was expecting 100 mega ohms.

[stj]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

mov1 is the empty outline
d1,2,3,4 form a bridge rectifier circuit - check none are shorted.

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Thanks everyone.

I previously performed a test on the transformer with the power on, and I got a result I wonder if you could explain.
It involves getting a 5 V reading when placing only one probe onto one of the transformer wires and leaving the 2nd probe unattached. The multi-meter is a RS Beckman T100B and it is battery powered with no connection to anything else, including earth.

The transformer and meter were on a rubber mat and insulated from each other.
Also, the image was not the one I tested. I tested the adaptor with all of the components connected.

I have attached a Jpeg with windings A, B and C labelled. I also included the resistance of each winding.

Results

Transformer Winding A:
AC: With one probe about 5V
but both probes: 0.23 V negligible.
DC: 0V.

Transformer Winding B:
AC multi-meter setting: With one probe about 5V
but both probes: 0.23 V negligible.
DC multi-meter setting: 0V.

Transformer winding C:
AC: With one probe about 5V
but both probes: 0.23 V negligible.

I checked voltage across the two 4.7uF 400V capacitors on the input and there was no voltage on them. 0V. So they had not charged.

Note: I wrote negligible voltage meaning 0V but there was some fluctuation in the voltage reading even without connecting the meter.

My question is how am I reading 5V AC when only one probe is connected?

I was guessing that electrons went up the probe and registered on the meter, but I don't really have a proper explanation for that. I thought there had to be a circuit with a potential difference between the two probes to get a reading, but this gave a reading similar to the way a grounded oscilloscope does with only one probe and no earth connected.

How is there 5V AC on only one probe?

Any advice is appreciated.

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

PS: I have all of the components ready to make a current limiter, but I won't be putting it together right now.