A quick inspection for the Dell's power supply

[treez]

You could also buy yourself a diff probe...say a TA041....then you can probe it.
i presume the tny280 is set up as a flyback, so can you see if the input voltage is getting to it or not?
You are right you shoudl be able to see voltage between drain and source.....if its not working you should get the rectified hv dc...but if its working you will get the switching of the drain.

So are you gong to see that the TNY280 works first?

But Betwixt is right there is a connection that yuo can make with those pc power supplies that you need to make to get it to work....this is needed when you have the PSU removed from the PC, which is what you have done there.

 

[eagle1109]

Haven't done the check, but I did this naming of the parts:

 

[eagle1109]

Today I tried to shoot the problem, powered the PSU on, followed the 324V path to the transformers.

First I found the 324V on the right big one, then the same voltage is passed to the small one via 1 ohm 1/4W resistor and it turns out the resistor is cracked!

I replaced the resistor and powered on the unit again and there wasn't any voltage even the mains voltage is off, because the plus fuse is blown!

Should I replace the fuse and try again?








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Hi, could you please check my latest update to the thread?

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You could also buy yourself a diff probe...say a TA041....then you can probe it.
i presume the tny280 is set up as a flyback, so can you see if the input voltage is getting to it or not?
You are right you shoudl be able to see voltage between drain and source.....if its not working you should get the rectified hv dc...but if its working you will get the switching of the drain.

So are you gong to see that the TNY280 works first?

But Betwixt is right there is a connection that yuo can make with those pc power supplies that you need to make to get it to work....this is needed when you have the PSU removed from the PC, which is what you have done there.

Thanks for the tips, I checked the diff probe, I think it would be a nice tool to have, but how it works?

Yes, I hope you check my latest post today.

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OK, I connected another power cable and hoped it won't blow up something, but it went well.

I checked the voltages, now I'm getting 5V on the purple rail, but 0V on the other cables.

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Now this is my analysis for the two transformers. According to #22

The TNY280 is supplying the standby voltage, that's why I'm getting 5V on the purple rail.
The ICE2PCS02 is supplying the main output transformer, so if nothing on the output rails then this IC could be broken.

 

[eagle1109]

No voltage means it can't operate so something nearer the AC input is causing the problem. It may be that there is a 'PFC' (Power Factor Correction) circuit upstream that has failed but usually they still let enough power through that something shows, even if it is incorrect.

Some detective work is needed and I'm afraid without a schematic I can only give you general directions. Pin 4 (pin 3 is missing) should be connected to a transformer, you need to find the other transformer pin that connects to the same winding. Basically there are a few turns of wire around the transformer core and you need to find which pins they connect to. One is the TNY280 drain, the other is the power input side. WITH THE PSU DISCONNECTED FROM THE AC and after leaving it for several minutes to discharge, measure the resistance from the pin connected to the other transformer pins, you should find two pins that have a just a few Ohms between them. If you can't it means the transformer is faulty, if you can, the fault lies between the other pin and the big reservoir capacitor. I'm not sure what is between them but if you can send me a photograph of the underside of the board and mark where those two transformer pins are, I might be able work it out.

Brian.

Hi,
Could you check my latest posts, there was a cracked resistor, I replaced it and now I'm getting 5V on the purple rail.

 

[betwixt]

If you have the 5V present there is a good chance the fault is repaired. Don't forget to link the green to one of the black wires on the output plug to enable the main supply. The normal way a PC PSU works is the 5V supply (always present) powers the standby circuit on the motherboard. When you press the power switch to turn the computer on, the motherboard connects green to black to switch the main power on, when you 'shut down' your operating system it removes the connection so the main power turns off again. That way the software can control it's own power source.

Brian.

 

[eagle1109]

I'm connecting the green to the black all the time, it's always there. Should I take it off, and then power the PSU and then put the short between the green and black rails?

My idea is that, it doesn't matter if the short is there all the time, it just work immediately.

But still no power at output rails. I'm suspecting the ICE2PCS02 to be faulty, because I think the TNY280 is the switcher for small high frequency transformer to supply 5V standby voltage and ICE2PCS02 is for the bigger high frequency transformer to run the output voltages. I ordered ICE2PCS02 and waiting for it.

 

[eagle1109]

Hello,

I just received ICE2PCS02 lot days ago.

But before couple weeks, I was testing the PSU, but an accident happened ! The case was touching the cathode of a power diode on the hot side.

From the first inspection. I got two 0.1 ohm resistors broken with the main fuse. I don't know if they are all the faulty parts.

This is my video today: