Broken Tenma supply

[dmowziz]

I checked the mains plug.. there is continuity from one end of the wire to the other

When the switch is pressed, it makes connection, continuity


Thanksss

I'll show you a pic of what's left inside (a little pcb). will measure the primary side again..

[SiriusHardware]

I checked the mains plug.. there is continuity from one end of the wire to the other

Sorry, does that mean you now have a resistance between the live pin of the plug and the neutral pin pf the plug?

Or you you mean that you have checked continuity of the live wire from the live pin on the plug to the other end of the cable inside the unit, and continuity of the neutral wire from the neutral pin of the plug to the other end of the cable inside the unit?

The switch probably has two separate sections inside it which switch the live side of the power and the neutral side of the mains power. Failure of only one section of the switch would stop the unit from working. Are both sections of the switch definitely OK?

[dmowziz]

Originally Posted by SiriusHardware

Or you you mean that you have checked continuity of the live wire from the live pin on the plug to the other end of the cable inside the unit, and continuity of the neutral wire from the neutral pin of the plug to the other end of the cable inside the unit?

Yeah I meant this...

Yes, the 2 sides of the switch are ok


The image below is what's left...That pcb (labelled "AC selector")


This power supply, the neutral side inside the unit is not connected to anything... It should have been like that when the unit was working

[SiriusHardware]

Does your PSU have a Canadian type 'A' plug (two pin) or a Canadian type 'B' plug (three pin) fitted?

Either way, the neutral side of the AC power which you seem to be saying does not go anywhere inside the PSU should be going to somewhere. You mean it's just dangling inside the unit somewhere, not connected to anything? If not, what exactly do you mean when you say it isn't going anywhere?

The 'AC selector', is that marked with a choice of supply voltages, maybe 110, 220, 240? Is it set to exactly 110V now, not offset or half way between two settings?

Could you give the lens / window on your camera a bit of a clean, your images are quite smeary as though there is a smudge or fingerprint on the lens or lens cover. This is a potentially dangerous area you are working in so we need to be able to see everything as clearly as possible.

[dmowziz]

It's type B

Noo, there's no visible connection at all...Nothing dangling

Wait.. "L" Live?

Yeah...Nothing on the hot side.. strange


But it is the same as here : https://www.eevblog.com/forum/repair...er-fuse-broke/
The pictures posted on the site shows nothing on that side as well

[SiriusHardware]

That's a much better picture, but what is that black object in the picture, is it a socket with a 3-pin female plug plugged into it on the outside? Can you show us a picture of that side of it, with and without the plug plugged into it?

[SiriusHardware]

I am thinking that maybe that black socket assembly has a fuse holder built into it, in the bottom section as you look at it in your photo in #25. If so, it will carry the hot / live horizontally from that unpopulated (and dangerously bare!) metal strip across to the brown wire which is probably the ongoing live-out to the voltage selector / mains transformer.

If there is a mains fuse holder built into the socket it will be under a flip-out lid or in a flip-out caddy / holder on the outside facing side of the socket, you will need to get a thin flat screwdriver under one end of it and lever it out.

[dmowziz]

wowwwwwwwwwwwwwwwwwwwwwww

Thanks Sirius...
There is a fuse in the black socket
Do you still need the pictures you asked? I took them

But I think no need..I found a fuse in the black socket and it's damaged


Thanks thanks thanks...I think this is the problem because before it died, it seemed like it was an overheating problem
Wow, I will get a new fuse tomorrow and try


until then... Jesus calls me now, I have to respond

God bless you

[SiriusHardware]

OK, good work, but one more bit of advice before I disappear for the evening - if you are buying fuses, buy more than one because you don't know why the original fuse blew.

It may just have been a mood swing, but it might be that there is a real fault which you will have to get to the bottom of yet, so buy a few spare fuses, not just one.

[dmowziz]

Originally Posted by SiriusHardware

OK, good work, but one more bit of advice before I disappear for the evening - if you are buying fuses, buy more than one because you don't know why the original fuse blew.

It may just have been a mood swing, but it might be that there is a real fault which you will have to get to the bottom of yet, so buy a few spare fuses, not just one.

Thanks... I will

But I believe if I put the fuse, it will work.

[Diabolical Artificer]

On that power socket you can see the N connection goes up to a riveted connection with the blue N wire coming out further along the top. It could be the bottom of that N connection is loose. By rights it should be the live that's fused.

A good way to test if everything's OK on the AC is to take a resistance reading between live and neutral which will be the resistance of the mains transformer and any wiring to it.

Andy.

[SiriusHardware]

It is the live which is fused. The fuse is oriented horizontally across the bottom of the socket so that it carries the live from that 'unpopulated' metal strip across to the ongoing brown live wire.

The test you suggest was tried earlier and gave an open circuit result. The transformer primary resistances were measured and found to be low, but not short-circuit. The OP did not realise until just recently that the power socket had an integral fuse holder, where he found the fuse was blown.

It remains to be seen whether the fuse blew because of some problem further downstream.

[Station X]

Fuses do die of old age, but I always check for possible causes of their blowing before replacing them. In a situation like this I've found the most common causes to be short-circuit diodes in bridge rectifiers connected to the secondary winding or short circuit smoothing capacitors.

[SiriusHardware]

We don't really know enough about the OP's experience or ability at the moment, so perhaps the simplest approach in this case is to see if it blows a replacement fuse.

Those big toroidal transformers always have quite a vicious inrush at switch-on, if you were able to observe the fuse at that moment you might very well see the filament 'twitch'. If so, that is bound to weaken the fuse over time.

[Station X]

I wonder if it's a slow blow fuse?

[SiriusHardware]

Very possibly.

There are at least four more fuses on the low voltage side (Post #1, image #2), two of them appear to be closely associated with the bridge diodes. We have to hope that one of those would do the decent thing if there was a short-circuit bridge diode or secondary cap.

[dmowziz]

Up and running...

I think the fuse is the only problem cause of the way the power supply died

and it requires 10A fuse but the fuse in there was 6A


Thankss all

[SiriusHardware]

That sounds quite a high value for a mains input fuse (although we here have to remember that your mains voltage there is 110V rather than our 230V).

Glad it's working for you, you know where we are if you have any more problems.

[majoconz]

So there you are - always check the simple things first!

[dave cox]

I have a several not so dissimilar PSUs (300+ watt), and the large toroids have quite a habit of eating fuses, even 10A/250V ones in the IEC leads. I now use 13A and heavy duty IEC leads to suit such a fuse!