Hello all,

I have a component on a PCB I'm trying to troubleshoot for work and would like help in identifying the part I think could be faulty.

The pcb is for a power supply for fire apparatus strobe lights.

It is round cylindrical, stamped "0407" in picture.

Any help is appreciated.

 

It looks like it says ".01ohm" above the 0407. That would make it a 10 milliohm resistor. Probably a current sense resistor.

 

That looks like a resistor. On the PCB, it is marked as R5. Above the "0407", there are some interesting text, which I think is 0.01Ohm

 

It looks like it says ".01ohm" above the 0407. That would make it a 10 milliohm resistor. Probably a current sense resistor.

That's what I'd go with, its also to the heavy track to Q1 so highly likely a current sensor for the main chopper transistor.

If that's gone open; there will be other damage - so just replacing the *CONSPICUOUS* damaged parts will probably result in a bang when powering up.

 

Thank you for the quick replies.

So it seems this might be better left to the company that produced it to fix.

How would I test that resistor?

It appears to say .01 ohm 1% unknown on watts but with that to be determined I'm thinking it is same as this:

http://www.mouser.com/ProductDetail...EpiMZZMtlleCFQhR/za%2bDyGH%2bTnlsqwN/m3nuPak=

 

You could test it with an ohm-meter. It should read very close to zero ohms across it.

I wouldn't suspect a current sense resistor as a typical failure point due to the amount of current it would take to reach its power limit, and it doesn't really look burnt in the picture.

I'd agree with ian field that there may be multiple damaged parts. Troubleshooting a power supply without a schematic and an oscilloscope and quite a bit of experience is going to be quite a chore. Hopefully you can find a relatively inexpensive replacement or have the vendor swap it out for you.

... but yes, the Mouser part looks like a good equivalent resistor if it's the right size.

 

You could test it with an ohm-meter. It should read very close to zero ohms across it.

I wouldn't suspect a current sense resistor as a typical failure point due to the amount of current it would take to reach its power limit, and it doesn't really look burnt in the picture.

I'd agree with ian field that there may be multiple damaged parts. Troubleshooting a power supply without a schematic and an oscilloscope and quite a bit of experience is going to be quite a chore. Hopefully you can find a relatively inexpensive replacement or have the vendor swap it out for you.

... but yes, the Mouser part looks like a good equivalent resistor if it's the right size.

A bit more info would make a huge difference - does it have a SMPSU chip or is it self oscillating. If its self oscillating with a bipolar transistor, it can be a very simple circuit - the MOSFET version requires fairly complex gate control.

With a chip type, you can fire it up without the power transistor and check the PWM drive with a scope, which should vary if you vary the feedback voltage.

 

Copy, thank you all for your input. I dont have access to a scope, and I dont have a lot of expirience in this field so I think I'll just send this back to the company to fix.

 

I think I'll just send this back to the company to fix.

I would, too.

The way to guess a resistor wattage is the physical size of it. It's all about radiating the heat, and the surface area is most of the story. There are some highly rated resistors that look too small, and they are. You can tell because they burn the board or unsolder themselves. The resistor itself can survive the heat, but everything close to it suffers. This simple cylinder shape is one of the, "good" ones. Just measure it and expect the right wattage will be very similar in size.