The best fault analysis channel I know, this and Diode gone wild. Every one knows Dave Jones, but he likes to loose focus and take you for a walk quite often.
Great video no matter how much you think it was a failure. I enjoyed this because it was very detailed, explanatory and understandable.By far the best electronics repair channel! Thank you once again!
That was a good explanation of the working of this power IC. There must be some fault detection in the IC which is switching it off. You can check what makes this IC switch off from its documentation and trace the faulty component.
Once again, a very professional approach to fault diagnosis. You make this look so easy. Shame about the Inverters you looked at recently; probably all three are too far gone and not worth fixing.
That's a good idea! I wondered if the opto had failed. My final thought - it's not one of these PSUs that doesn't output unless there's a little load is it?
Yeah he didn’t mentioned it. This failure seems like a feedback issue. And he should use a oscilloscope and and isolation transformer as well, in my opinion, when troubleshooting a SMPS.
@@slobodanjovanovic8166 Likely no feedback, or the secondary side control is turning off the power supply. Either optocouplers are faulty, and the chip is going into overvoltage shutdown from the primary side supply, or the reference is either dead, or the resistors or ceramic capacitors in it have cracked or have broken traces. Then the primary side comes up, but the voltage rises above the trip threshold as there is no feedback from secondary, turning the controller off. Likely the secondary side has some power control there that will switch off the main 3V3 rails, and then run the chip in a low power mode through the second optocoupler, using a power rail that is higher voltage, but which is dropped down to give a standby 3V3 rail, so the controller is sitting at minimum switching frequency or in a burst mode to maintain a supply but use very little power.
Great channel. I think there is a fault on the secondary side. Check around the feedback loop. What probably happened is something failed on the secondary sound that caused the unit to go into shut down protection that eventually took out the chip.
even bad or partially shorted auxiliarry winding can do that shutdown so shutdown can be caused by bad copler bad refrence ic bad soldering in any part of the circuit bad transformer
There is not a lot on this board....if the run winding has continuity, most likely it would be something on the secondary. I would just replace the 2.5 reference, and test one by one with known good optocouplers (i believe there are three on this board). What is the 8pin IC on the secondary? Thank you for all the great videos !
It may be a bad opto-coupler or associate TL431 if any ? Because it looks like the first impulse is arriving on secondary section, but does not sustain missing feedback to the chip.
As many others said below. Something wrong with the secondary feedback. Notice how it climbs very quickly to nearly 3.6 volts, then shuts down. Nothing telling it to quit building voltage, until the protection circuitry kicks in to shut the whole thing down. Although I am kind of curious about the current sense resistor. What is the maximum voltage drop across it when using Min/Max before the secondary shuts down? Maybe that sense resistor has gone high resistance or even opened up??
I guess it's a no load issue. He should try load this power supply and check. Because one time I have faced one smps which was good after replacing some power semiconductors. But when I turn smps on it shows similar behavior. Then I was connected load which was 80% load for power supply output rail and smps output was stabilized.
If it has a built in load resistor then its not necessary but if it doesn't then yes you are right i have had this symptom without load it shuts down. I hope Norcal makes a follow up video.
I know what you were told and looking at the circuit it may not initially be obvious of an "Over Voltage state" So is it possible the power supply in fact does rely on a proper load before current ergo the correct Voltage and current is outputted?
The best fault analysis channel I know, this and Diode gone wild. Every one knows Dave Jones, but he likes to loose focus and take you for a walk quite often.
Great video no matter how much you think it was a failure. I enjoyed this because it was very detailed, explanatory and understandable.By far the best electronics repair channel! Thank you once again!
I dont do much switching power supply work. Found this very interesting. Thank you sir.
Wow, would really like to know what this fault is...
As usual great troubleshooting with expert visual and explanations of circuit signal paths.
Nice explanation of the IC. Excellent Video as always!
That was a good explanation of the working of this power IC. There must be some fault detection in the IC which is switching it off. You can check what makes this IC switch off from its documentation and trace the faulty component.
Great explanation of how SMPS works, Try replacing the optocouplers
Once again, a very professional approach to fault diagnosis. You make this look so easy.
Shame about the Inverters you looked at recently; probably all three are too far gone and not worth fixing.
One inverter was approved and parts are on order.
I would try a 2.5v reference (from bench ps) on ic pin3 and check output dc.
That's a good idea! I wondered if the opto had failed. My final thought - it's not one of these PSUs that doesn't output unless there's a little load is it?
Might be a short on the output.. Id try applying 3.5v dc to the output and see if there is a current draw
Looks like feedback issue. If you didn't, you should check reference regulator and optocouplers.
Have you checked optocouplers?
Yeah he didn’t mentioned it. This failure seems like a feedback issue. And he should use a oscilloscope and and isolation transformer as well, in my opinion, when troubleshooting a SMPS.
Ummm -.thank You all, actualy I'm facing similiar problem, there is 18vdc on bootstrap caps -.but not output voltage on secondary
Since the controller chip is giving the initial pulse, it looks like it is working properly, but there is no feedback.
@@slobodanjovanovic8166 Likely no feedback, or the secondary side control is turning off the power supply. Either optocouplers are faulty, and the chip is going into overvoltage shutdown from the primary side supply, or the reference is either dead, or the resistors or ceramic capacitors in it have cracked or have broken traces. Then the primary side comes up, but the voltage rises above the trip threshold as there is no feedback from secondary, turning the controller off.
Likely the secondary side has some power control there that will switch off the main 3V3 rails, and then run the chip in a low power mode through the second optocoupler, using a power rail that is higher voltage, but which is dropped down to give a standby 3V3 rail, so the controller is sitting at minimum switching frequency or in a burst mode to maintain a supply but use very little power.
Great channel. I think there is a fault on the secondary side. Check around the feedback loop. What probably happened is something failed on the secondary sound that caused the unit to go into shut down protection that eventually took out the chip.
Don't give up buddy, find the short in the board, you can do it.
If you figure it out please make a follow up video, like always thank you.
even bad or partially shorted auxiliarry winding can do that shutdown
so shutdown can be caused by
bad copler
bad refrence ic
bad soldering in any part of the circuit
bad transformer
There is not a lot on this board....if the run winding has continuity, most likely it would be something on the secondary. I would just replace the 2.5 reference, and test one by one with known good optocouplers (i believe there are three on this board).
What is the 8pin IC on the secondary?
Thank you for all the great videos !
It may be a bad opto-coupler or associate TL431 if any ? Because it looks like the first impulse is arriving on secondary section, but does not sustain missing feedback to the chip.
What’s on the feedback?
As many others said below. Something wrong with the secondary feedback. Notice how it climbs very quickly to nearly 3.6 volts, then shuts down. Nothing telling it to quit building voltage, until the protection circuitry kicks in to shut the whole thing down. Although I am kind of curious about the current sense resistor. What is the maximum voltage drop across it when using Min/Max before the secondary shuts down? Maybe that sense resistor has gone high resistance or even opened up??
optocouplers replace.reference resistor.
I agree, he has to check the entire feedback circuit. Even the KIA431 if it uses it. bravo yiorgo. Eisai ellinas!!
@@skytvod yes
Wonder if it required a load after all.
I tries various resistive loads, still no go
Maybe you need the load after all
I did try various loads and same results
I guess it's a no load issue. He should try load this power supply and check. Because one time I have faced one smps which was good after replacing some power semiconductors. But when I turn smps on it shows similar behavior. Then I was connected load which was 80% load for power supply output rail and smps output was stabilized.
I did try various loads and same results
Wouldn’t the supply require a load to sense it being connected to the logic board?
If it has a built in load resistor then its not necessary but if it doesn't then yes you are right i have had this symptom without load it shuts down. I hope Norcal makes a follow up video.
I did connect various loads and still the same results
It’s unfortunate the customer did not include the main board.
I know what you were told and looking at the circuit it may not initially be obvious of an "Over Voltage state" So is it possible the power supply in fact does rely on a proper load before current ergo the correct Voltage and current is outputted?
I did connect a load and had the same results.
does it have a feedback on low volt side from output connector, IE some return saying yes its running and ok.
It has only supply voltage out and a stand alone thermistor to send temperature to the logic board
Huh I don't feel so bad I have been working on an Apple HiFi power supply for the last year on and off with little success . These things are VooDoo .
cant win em all :o)