Rewinding burnt choke coil

[Per Hansson]

Re: Rewinding burnt choke coil

Hahaha, that PSU is so baked even the solder melted on the underside, wow!
The PCB topside needs to be fixed first, if it's too bad it's not worth it IMO.
And you can throw the coil away: the core is toast and needs to be replaced.
But just jerry rigging it would work, it requires s scope for testing though.
I would recommend you get a analog scope on eBay instead of some crap digital thing as you mentioned.
It will allow you to learn allot more, and get a deeper understanding.

P.S: This PSU failed because of the use of general purpose caps, the switching converter UC38458 it uses supports operation at 500Khz!

[budm]

Re: Rewinding burnt choke coil

It is switching power supply so low ESR, 105c caps should be used, get one with the highest ripple currrent rating you can get.

[Stefan Payne]

Re: Rewinding burnt choke coil

The thing is the caps had already been replaced once approximately a month ago....yeah, they're Samwha so I'm not claiming they were super high quality

Samwha shouldn't be that shitty.

But that doesn't help, if you choose a totally wrong series like RD wich is a general purpose one. I'd imagine that the original were something like CapXon KF or other low ESR capacitors.

So no wonder that General Purpose one died within a Month or so and possibly caused even more damage due to improper usage of the cap.

Anyway:
That PCB looks really messed up...

Has it possibly become conductive due to heat??


@stj
Do you think general purpose caps are OK for this application/PSU??

[Dannyx]

Re: Rewinding burnt choke coil

in that case, maybe the output diode(s) are leaky and the caps & coil got hit with ac!

actually if you think about it, that makes sense - because it could have killed the fan!

There's only one output diode, visible near the coil, just FYI...could indeed have some leakage :|

[Dannyx]

Re: Rewinding burnt choke coil

The DC output caps failed and that caused too much stress on the choke. For me, I'd put that thing in my parts bin and buy a bigger PSU. It looks almost identical to these PSU's ali sells for like 25 bucks.

Not like I need one right away, so I thought I'd go down the cheaper and more DIY route and try to fix what I already have

[stj]

Re: Rewinding burnt choke coil

The thing is the caps had already been replaced once approximately a month ago....yeah, they're Samwha so I'm not claiming they were super high quality

in that case, maybe the output diode(s) are leaky and the caps & coil got hit with ac!

actually if you think about it, that makes sense - because it could have killed the fan!

[CapLeaker]

Re: Rewinding burnt choke coil

Yes, I figured as much. I could probably bypass it entirely but I'd get more noise on the output...I have no idea why it ended up in such a state other than the fan jamming and the load being slightly over the PRACTICAL limit, not the one on the label...

The DC output caps failed and that caused too much stress on the choke. For me, I'd put that thing in my parts bin and buy a bigger PSU. It looks almost identical to these PSU's ali sells for like 25 bucks.

[Dannyx]

Re: Rewinding burnt choke coil

I was reading through this....yeeeeeeaah right...apparently what I'm trying to do would send the entire "coil community" in an uproar The biggest issue is the coating on the cores since I have no idea what it is or what it's made from so I can try to replicate it...

[Dannyx]

Re: Rewinding burnt choke coil

BTW, what is this power supply rating anyway, the coil is so big, looks like it is made for very heavy load.

Says 10A on the label, so at 12v that would be 120w. I can provide actual models for key components like the transistor and the diode if you wish You can bump the output up to around 14.5V via that pot near the output block which makes me think it could be used as a crude battery charger....probably not

[budm]

Re: Rewinding burnt choke coil

BTW, what is this power supply rating anyway, the coil is so big, looks like it is made for very heavy load.

[Dannyx]

Re: Rewinding burnt choke coil

look at the caps.
maybe one went low-resistance and caused a load increase through the choke.

The thing is the caps had already been replaced once approximately a month ago....yeah, they're Samwha so I'm not claiming they were super high quality

[stj]

Re: Rewinding burnt choke coil

look at the caps.
maybe one went low-resistance and caused a load increase through the choke.

[Dannyx]

Re: Rewinding burnt choke coil

The common mode choke is the one right next to the incoming AC fuse. That Toroid is for some other function, more like a choke for Pi filter in the DC output.

Yes, I figured as much. I could probably bypass it entirely but I'd get more noise on the output...I have no idea why it ended up in such a state other than the fan jamming and the load being slightly over the PRACTICAL limit, not the one on the label...

[budm]

Re: Rewinding burnt choke coil

The common mode choke is the one right next to the incoming AC fuse. That Toroid is for some other function, more like a choke for Pi filter in the DC output.

[Dannyx]

Re: Rewinding burnt choke coil

common mode choke has + and - both going through it.
that's just a regular choke.
have you got a scope?

I thought so too - it's what's used in the AC input filtering of a SMPS.
Sadly no I don't have a scope....yet I was thinking of getting one of those Ebay kits as a starter, since a pro scope would not only be beyond my budget at the moment but most of its features would also be kinda useless, thus making it a waste of money...

[stj]

Re: Rewinding burnt choke coil

common mode choke has + and - both going through it.
that's just a regular choke.
have you got a scope?

[Dannyx]

Re: Rewinding burnt choke coil

I'd replace the whole choke. As it has already been said before, the heat probably damaged the core. So even if you would rewind it, it wouldn't be the same as it was.

Where would somebody have a chance to find such thing ? I don't know its value or anything....I'm only able to measure the physical characteristics like the total length of wire and diameter of the two rings. Each wire is 75cm in length (there's two pieces parallel to each other) for instance.

[CapLeaker]

Re: Rewinding burnt choke coil

I'd replace the whole choke. As it has already been said before, the heat probably damaged the core. So even if you would rewind it, it wouldn't be the same as it was.

[Dannyx]

Re: Rewinding burnt choke coil

That's another thing I need to mention: the coil was covered in some sort of paint or coating which has fallen off due to the heat so I stripped it down entirely just so it's nice and clean and I'm now down to the bare ferrite...would this still work ? It's in series with the positive rail. Is this called a common mode choke, or are common mode chokes only used in the mains filtering portion of a SMPS ? I never understood this "common mode" business :|

[goodpsusearch]

Re: Rewinding burnt choke coil

The core material has probably lost its properties.