Thanks
I just might make one!

 

You guys are old. Just kidding, I am sure I am pretty close to the same age give or take.
Back to my topic for a second. On these SMPS, what do you guys do to test the small transformers? Static testing for continuity is one method but is it accurate? I like dynamic testing so should I put power to it and see what it does?

There used to be a shorted turns tester by Dick smith Electronics, but it was intended for horizontal flyback transformers and could give a false fail on SMPSU transformers.

Most "old hand" service engineers put a 60W light bulb in place of the mains fuse - but it doesn't always limit the current enough. The filament also has a PTC characteristic, so there is a switch on surge.

Some people use a variac - but some SMPSUs have UVLO and suddenly fire up as you cross the start up threshold. A PFC front end will probably burst into life somewhere in the region of 85V - but at least its a lot less energy to go bang with.

 

There used to be a shorted turns tester by Dick smith Electronics, but it was intended for horizontal flyback transformers and could give a false fail on SMPSU transformers.

Most "old hand" service engineers put a 60W light bulb in place of the mains fuse - but it doesn't always limit the current enough. The filament also has a PTC characteristic, so there is a switch on surge.

Some people use a variac - but some SMPSUs have UVLO and suddenly fire up as you cross the start up threshold. A PFC front end will probably burst into life somewhere in the region of 85V - but at least its a lot less energy to go bang with.

Yes you are correct about the Variac, a good idea with some is to use a series bulb and a variac set to about 90volts as a starting point. My version of the Dick Smith ring tester is still going strong and as no ring tester is 100% foolproof I use mine and a scope so that I can actually see the ringing. I also think that repairing smp's can be a bit of a black art until you've gained a fair bit of experience and a good understanding of the various sections and their purpose. Also, be aware that there is often a feedback system that relies on the correct loads being in place. without them, results can be very unpredictable. Often there are secondary sub supplies that add to the fun!
There has been quite a bit of interest in the subject, and the fact that linear power supplies are becoming rarer, the future seems to be that unless you can understand smp's and know how to SAFELY work with them, we will either have to buy off the shelf ready made (from who knows where) units, or build/modify/repair them ourselves. This of course puts us into the realm of high voltage working, and the mains supply.

For what it may be worth, I will put together a thread based on my own experiences and techniques that served me well for many years. hopefully, others will add their input.

 

Yes you are correct about the Variac, a good idea with some is to use a series bulb and a variac set to about 90volts as a starting point. My version of the Dick Smith ring tester is still going strong and as no ring tester is 100% foolproof I use mine and a scope so that I can actually see the ringing. I also think that repairing smp's can be a bit of a black art until you've gained a fair bit of experience and a good understanding of the various sections and their purpose. Also, be aware that there is often a feedback system that relies on the correct loads being in place. without them, results can be very unpredictable. Often there are secondary sub supplies that add to the fun!
There has been quite a bit of interest in the subject, and the fact that linear power supplies are becoming rarer, the future seems to be that unless you can understand smp's and know how to SAFELY work with them, we will either have to buy off the shelf ready made (from who knows where) units, or build/modify/repair them ourselves. This of course puts us into the realm of high voltage working, and the mains supply.

For what it may be worth, I will put together a thread based on my own experiences and techniques that served me well for many years. hopefully, others will add their input.

Some laptop "power bricks" had primary side voltage sensing - the regulation under load was pretty rubbish. The laptop itself usually has a regulator section of its own, so "power brick" stability is far less important. This practice seems to be dying out, later models seem to have far better regulated "bricks".