After confirmed that the power FET is shorted my next move was to check on the primary winding of the main transformer

What not good should i see if there is a problem? Something with my eyes? Or some check with DVM or osciloscope - is it done on the board or i should unmount the main transformer?

Question #2
I found the current sense resistor have problem and the value increased from 0.18 ohm to 0.24 ohm when tested with Blue ESR meter. Please see the photo below.

Can this check be done with DVM or not? If not can i do the check with "basic" ESR meter like mine /TS-M8N Transistor Tester Diode Triode Capacitance ESR Meter MOSFET NPN/PNP/ or i should use the "Blue esr meter"

Nice day!

 

There are usually two fets on an atx psu in pushpull mode, and two more on the slave winding, never known a transformer to blow up, change both fets and the resistor, any other silicon devices like diodes on the output side, then wait for the next bang...

 

Hi,

Without a doubt check the electrolytic caps, at least the bigger ones. They go and that causes problems.
I've had two power supplies of my own fail to operate because the filter caps aged and no longer could perform the correct filtering action. Replacing those caps in both instances repaired the problem for both.

 

One thing which blows up the FETs is the snubber capacitors reducing in value.

 

Unfortunately the Google Dictionary does translate the word snubber into some word that no one from Bulgaria i think can understand.

Could you tell it other way

 

When the FETs switch off, the transformer primary generates a large back emf which can exceed the rating of the FET (voltage or dV/dt). To solve this there is a circuit across the transformer winding which uses a capacitor, resistor, and sometimes a diode. Over time the capacitor can lose capacitance and this causes the peak voltage to rise and eventually lead to failure of the FETs. If only the FETs are replaced then they are going to fail again.

 

After confirmed that the power FET is shorted my next move was to check on the primary winding of the main transformer

What not good should i see if there is a problem? Something with my eyes? Or some check with DVM or osciloscope - is it done on the board or i should unmount the main transformer?

Question #2
I found the current sense resistor have problem and the value increased from 0.18 ohm to 0.24 ohm when tested with Blue ESR meter. Please see the photo below.

Can this check be done with DVM or not? If not can i do the check with "basic" ESR meter like mine /TS-M8N Transistor Tester Diode Triode Capacitance ESR Meter MOSFET NPN/PNP/ or i should use the "Blue esr meter"

Nice day!

You near certainly need a shorted turn tester for the transformer - DSE used to do a kit but not anymore AFAIK. The schematic is floating about online, and AFAICR: There's no unobtanium on the parts list.

An ESR meter is probably as good as it gets for low value resistors, but its outside its intended purpose - measure some known good samples to verify the results.

Shorted secondary side rectifiers aren't exactly rare, the overload protection circuit is supposed to stop that letting the magic smoke out - but it doesn't always work like that!

 

@UnnamedUser159
May help.
Max.

 

Hey;

I began to check new PSU.

Everytime altough my order(every desoldered item to goes in 1 bag) and everything to be described in One text file the thing are going not fine.
It`s maybe normal when i learn to do something new. Other reason is that now i have osciloscope and the method of analyze is different that only DVM...Enough off topic

This patient is TurboX 650W ZU-0150A.

All EC visually seems good. The tester is showing only 5v stb. I have the base blue variant which does only show acceptable/bad voltages but not the values and other

Thanks

The STB voltage is 5.15

5 12 and 3.3 are not available

 

Do you have a link wire between the green wire and one of the black wires?

 

Of course. With paper clip

 

The other thing that might stop it working is that some of these supplies require a minimum load, otherwise they shut down.
https://mysite.du.edu/~etuttle/electron/elect62.htm
"Computer power supplies were designed for that purpose, not as a laboratory supply, so if we use them for this purpose, we must be sure to provide a proper environment. They are switching supplies, which always demand a minimum current output. In a computer, this load is always connected, but in a laboratory supply it is not, and we must provide it. Some switching power supplies (especially those intended for laboratory use) have an internal load. A computer PSU cannot be assumed to look into an open circuit, unless you have the correct specifications, and they say so. A modern ATX supply has minimum loads of about 1A on the +12 supples, 0.3A on the +5V, and 0.5A on the +3.3V. The -12V and the +5V standby ouput have no minimum current. These figures can be used as a general guide if the exact specifications are unknown.

I used 12Ω, 3W sand power resistors in parallel as a load for +5V and +3.3V, which gives currents of 0.83A and 0.55A. These currents will not be missed. For +12V, I used a 20Ω, 10W sand power resistor, which gives a current of 0.60A. These resistors were soldered to 7-terminal tie point strips (also available from All). The power dissipation is less than the ratings, but the heat will be present, so the resistors should be supported in the air and not touching anything."

 

I am sure that the PSU is not working. It`s on one my friend.

If i know right the computer PSU tester can be used as dummy load

Maybe i am not doing the following : to put the tester to run the PSU and then measure the yellow red and orange cables than Black one(not on the motherboard outputs)

 

Hey;

I began to check new PSU.

Everytime altough my order(every desoldered item to goes in 1 bag) and everything to be described in One text file the thing are going not fine.
It`s maybe normal when i learn to do something new. Other reason is that now i have osciloscope and the method of analyze is different that only DVM...Enough off topic

This patient is TurboX 650W ZU-0150A.

All EC visually seems good. The tester is showing only 5v stb. I have the base blue variant which does only show acceptable/bad voltages but not the values and other

Thanks

The STB voltage is 5.15

5 12 and 3.3 are not available

Electrolytic capacitors can look "not quite right" when going down. Frequently the tops bulge when they vent, but they can look slightly concave if lost electrolyte causes a vacuum and sucks the top in a bit. The electrolyte accounts for a fair bit of the weight - sometimes it absence is obvious with the part out of the board. SMPSU electrolytics get hot when failing, damage to the plastic sleeve is sometimes obvious.

Most SMPSU regulators only sample the 3.3 & 5V outputs - with no load; they just run up to voltage and the PWM ratio settles back to idle. that means you can't draw current from any of the non sampled rails.

 

Most SMPSU regulators only sample the 3.3 & 5V outputs - with no load; they just run up to voltage and the PWM ratio settles back to idle. that means you can't draw current from any of the non sampled rails.

Or, more often, they can't get the pulse width low enough and the output voltage goes too high and the overvoltage protection shuts it down. That's why you need some load on the outputs.

 

So..

If i understand right i can find bad caps from this bulge /which everyone does know/ but from this concave too.

How to proceed now? Desolder all EC and put new one or i can make some measurements with osciloscope and find bad one by "Lazy" way?

 

Have replaced some capacitors i have marked on picture2, put two screws by diagonal for grounding and now it does light on tester for a second and then goes 5v stb only

 

So..

If i understand right i can find bad caps from this bulge /which everyone does know/ but from this concave too.

How to proceed now? Desolder all EC and put new one or i can make some measurements with osciloscope and find bad one by "Lazy" way?

Testing by replacement is a popular option - as long as you use suitable low ESR parts.

Bulged or concave tops isn't the only sign to look for - If the soldering looks dodgy I start there, sometimes when I hit a particular solder joint, I get a fishy/rubbery nasty smell. Usually an electrolytic will be on the other side, and one of its leads will be badly corroded. Sometimes electrolyte leaks and spreads across the board - but can be hard to distinguish from the glue sometimes used to secure the components.