What's Causes the NASTY Looking Corrosion around the Main Smoothing Bulk Capacitors in PSU?

[@hernancoronel]

At 20:59 red lead is not making contact! Got you Richard 😂! Thanks for the excellent video!

[@yoyomismo2052]

This type of power supply are great for recovering copper wire to repair traces. The PFC has the bigger wire around 0.7 mm (and is the difficult to recover all cover in metal) the 3 transformers in board can give you around 4 different diameter wires (and very easy to break the ferrite to open) plus the wires off the power supply (if is copper to)

[@analoghardwaretops3976]

Each resistor across the individual series DC link ( bulk) caps are mainly for maintaining the voltage across each approximately equal ... The leakage current in individual caps may be different & vary over time & with temperature..so" current balancing" resistors are calculated , to bleed (25- 30)% more than cap. leakage current ( as per its data sheet specs....)

[@marauderofdeath6401]

Another great video! Always learn something by watching these!

[@myblack6636]

at 2:10 there might be a diode with a corroded leg near by those 2 common mode chockes. Great vid.

[@fflynnful]

The 150k ohm resistors are just some bleeder resistors to keep you from knocking yourself backwards by bleeding off the primary voltage and the material you scraped from the board may be just some glue to hold the capacitors in place. The cracked solder connections would likely have caused this PSU to malfunction.

[@shagreobe]

Thanks Richard, keep em coming!

[@alanrichardson1672]

Hi Richard, I think it may be useful to explain exactly what PFC is all about, perhaps a mini video topic. 😊

[@LearnElectronicsRepair]

I've covered on several videos in detail but never made a specific one about it. Thanks for the suggestion, I'll get on to it

[@Dutch_off_grid_homesteading]

Heya yes that was some time ago nice to see you still doing pws

[@graeme8755]

Hi Richard, Between the bottom of the meter and the socket you are testing for ohms. The transformer in the background, can I see bare wire on the transformer winding. This image is at the 22:13 mark of the video.

[@LearnElectronicsRepair]

I don't think that is what it is, if you are referring to what I think you are, a few seconds later you see the whole inductor (not a transformer). It has two enameled windings, one enamel clear and one red.

[@strelatronics5533]

I think you could've scraped it off more easily if you had heated it up a bit. Love your videos Richard

[@grahambambrook313]

I think the resistors serve a dual purpose, a) to act as a safety drain & b) to equalise the voltage across the capcitors.

[@Pulverrostmannen]

The resistors are actually very important when caps are put in serial to each other, since no capacitor is equal in capacitance and also leakage current the voltage would drift making one cap overcharge while the other goes low. it is probably why one cap is bulged because it likely been overcharged. the resistors are primary for equaling voltage and they work like a voltage divider and then they act as a discharge as well

[@LearnElectronicsRepair]

@@Pulverrostmannen That is a really interesting insight, as the resistor across the bulged capacitor was open circuit. This is something I didn't know, I have learned something today. Thank you 🙂

[@Pulverrostmannen]

@@LearnElectronicsRepair no problem :) we are all here to learn together. I enjoy your videos

[@TonyLing]

Thanks mate, I learned a few things there

[@akierum]

Why nobody shows psu repair with current injection like all laptops, phones etc.

[@rodbhar6522]

I know nothing about this kind of circuit, but it seems to take 220VAC, rectify and smooth it, then through the switching transistors and LLC turn it back to AC! What is the point? Is the frequency different?

[@stargazer7644]

That's exactly what it does. And then on the other side of the transformer, it rectifies it again and turns it back to DC! The reason for this is the AC it converts it to is much higher frequency (usually hundreds of kHz or maybe up to 1 MHz) rather than the mains 50/60 Hz. This allows the transformer to be much smaller and far more power efficient. These PC power supplies provide between 300 and 1200W in a small, light, power efficient package. If you were to try to build a conventional linear supply with just a 60 Hz transformer with those specs, it would be the size of the entire PC, and would weigh 50 pounds just for the power supply.

[@rodbhar6522]

@@stargazer7644 Cool! Thanks!

[@norbert1439]

many thanks from germany.....73 de DF6WO

[@Lightrunner.]

😱Many defects in this psu . Ohh,, Richard . With what frequency did you measure the main caps esr??.

[@LearnElectronicsRepair]

My ESR meter is 100KHz

[@Lightrunner.]

@@LearnElectronicsRepair Hi, you now that main caps after the brigde rectifier work with 50 Hz . Your meassure frequenz ist to high and the esr value ist consequently wrong. /. Sorry

[@CXensation]

The main caps are meant to work as power reservoir caps. These cap types are not optimised for HF filtering.

[@Lightrunner.]

@@CXensation you mean not Lf or Hf optimize. It is a middle frequenzy cap value 🤔

[@LearnElectronicsRepair]

@@Lightrunner. I do believe I mentioned in the video that these are not really lowESR capacitors but let's measure them anyway, they will probably read quite low. Actually I don't think ESR matters with this type of capacitor application. As I didn't have any suitable repalcements and I am fairly convinced at least one of them is bad, I wanted to test (on video) if the PSU would actually run with them. It did, but may not run so well load I suspect. Really the purpose of the two caps in series is to put approx 160V on the other end of the LLC network. I thought it was a good opportunity to experiment.

[@2009numan]

those psu testers aren't always any good becuase they don't put any load on the psu

[@CXensation]

They are not used as a load or performance tester. They are meant to be a basic tester showing the output voltages at PSU no load condition. This gives an instant indication of the voltage circuit condition which is what you want for a basic go/nogo test. If you need to load test the PSU, you will need a much more elaborate setup. I recommend a bunch of automotive headlight bulbs for a cheapo heavy 12V test load. That would instantly show a weak PSU.

[@2009numan]

@@CXensation yes the voltages can show as ok but it doesn't mean the psu will be ok when used with a load on it

[@gordslater]

If you need a good load for a PSU wind some glavanised steel fence wire in a spiral on a large wooden cross frame as a support. Use heat-resistant connection blocks like ceramic ones (plastic will melt - the steel wire can get quite hot over time) Different diameter fence wire have different resistances (and fusing currents haha) I've tested 48V 250A PSUs into some loads made this way and they are cheap to make and work well - aim a large box fan or 24 inch room fan at them if they get too hot for huge PSUs. Wirewound resistors get expensive at the 200W level and also require huge heatsinks so a few quid for a roll of fence wire and a few quid for a couple of ceramic terminal blocks is a good compromise - spend the money saved on ciggies and drink

[@CXensation]

@@2009numan As I wrote: This tester was never meant to do that. If that is your test requirement, you'll have to find equipment that suits your demand.

[@LearnElectronicsRepair]

@@gordslater That sounds like a fun idea to play with 😉

[@eamonhannon1103]

No the two resistors are there to ensure the voltage across the two capacitors is the same . If the resistors were not there the voltage might not be evenly distributed between the two capacitors .

[@robtitheridge9708]

I have noticed that the youtubers that fix games consols never attempt to repair the power supplys ,not sure why that is as it seems like a good money maker ..

[@JonnyMac351]

Probably because a lot of them don't have much electronics knowledge i saw one trying to repair a PS1 power supply that was blowing fuses he didn't know what to check (there was only 3 power devices that could have caused it basic power supply) so his solution was put a bigger fuse in and see what blows up.

[@jimnicosia5934]

Just put a bandaid on it.