how to step by step debug about SMPS

[wei9321]

how to debug about SMPS

when the SMPS occur a bug,
how do you debug?
ex: no output,outut unstable,output short ....
can you list the step about debug?
thanks!

 

[Tahmid]

how to debug about SMPS

Hi,

Identify the PWM IC. Check if you get a pulse at the PWM IC output. Check the pulse with an oscilloscope and see if it seems fine. Ensure the frequency seems fine.

Check the MOSFET/IGBT devices and check if there is any short across them. Check resistors and/or zeners near the MOSFET/IGBT to see if any have burnt out.

Check the output rectifier(s). See if you can detect a short-circuit. Check the output capacitors to see if they have leaked or not and check the capacitance and compare against the marking on the cover of the capacitor(s). Check inductors to see if any have burnt out.

Check the PCB traces to see if anywhere the traces are burnt.

Check the feedback circuit, ie, the shunt-regulator and associated components.

And lastly check the fuse to see if that fused out. Check the input capacitors.

Hope this helps.
Tahmid.

 

[wei9321]

Re: how to debug about SMPS

Hi,

Identify the PWM IC. Check if you get a pulse at the PWM IC output. Check the pulse with an oscilloscope and see if it seems fine. Ensure the frequency seems fine.

Check the MOSFET/IGBT devices and check if there is any short across them. Check resistors and/or zeners near the MOSFET/IGBT to see if any have burnt out.

Check the output rectifier(s). See if you can detect a short-circuit. Check the output capacitors to see if they have leaked or not and check the capacitance and compare against the marking on the cover of the capacitor(s). Check inductors to see if any have burnt out.

Check the PCB traces to see if anywhere the traces are burnt.

Check the feedback circuit, ie, the shunt-regulator and associated components.

And lastly check the fuse to see if that fused out. Check the input capacitors.

Hope this helps.
Tahmid.

sorry,
"Check the output capacitors to see if they have leaked or not and check the capacitance and compare against the marking on the cover of the capacitor(s). "
this paragraph, i can't understand it clear,
can you give an example ?
thanks!

 

[karesz]

how to debug about SMPS

Hi,
if it leaks you will see some (ACIDIC!) fluid around_it is very in detail to clean, with much water...
Maybe you ca not see an outgoing fluid around capacitor, but some changed conture/shape of metal can, lane of more gasous content, hump on the cover cup...
Compare against marking: is it populated with the right polarity or maybe wrong!?
K.

 

[Tahmid]

how to debug about SMPS

When the capacitor leaks, you'll some some fluid around the capacitor. Sometimes the capacitor's shape becomes abnormal. eg. it may become inflated.
Check the capacitance of the capacitance with an LCR or similar meter and compare this capacitance with the value marked on the body of the capacitor.
Check the polarity of the capacitor.

Hope this helps.
Tahmid.

 

[rajudp]

how to debug about SMPS

better check with LCR meter , i have faced many problems with capacitor value change and the capacitor look good

 

[Kripton2035]

how to debug about SMPS

this link is a VERY good start ...

https://www.repairfaq.org/sam/smpsfaq.htm

 

[brunofunchas]

Re: how to debug about SMPS

For me the best tool to test capacitors is an ESR meter.

Regards,
Bruno

 

[Kripton2035]

Re: how to debug about SMPS

For me the best tool to test capacitors is an ESR meter.

for me too ...
everything is explained in the link I gave just before you ...