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Post by justgreg on Feb 27, 2015 12:28:48 GMT -5
5.0v 2.0A
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Post by mastertech on Feb 27, 2015 12:39:03 GMT -5
Do you have a power strip with a switch on it to turn it on and off?
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Post by justgreg on Feb 27, 2015 12:52:31 GMT -5
I have a spare one somewhere. You thinking over voltage power surge?
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Post by mastertech on Feb 27, 2015 13:08:23 GMT -5
No, it is needed for next test.
There looks to be 3 possible parts to cause the problem. You have to find which one. The regulator, the diode or the cap at the lower right of the regulator. The resistor at the right of the regulator would probably not cause the problem.
So what I want you to do is flow some solder across the top of the blown fuse to connect the circuit. If you have difficulty with this then use a piece of wire. Once connected, plug in the power strip and turn it off. Plug the devices P/S into the power strip and into the device.
Now, when you turn on the switch, 1 of those 3 parts is going to get real hot. Only turn the switch on for a second or 2 because we do not want to damage anything else. If you need to switch on a couple times to get a feel for the hot device that is ok, just do it in short intervals.
If you do not have good feeling in your finger tips you can put a dab of solder paste on top of each component and see which melts first.
Let me know what you get.
Oh, and don't be surprised if the component pops so wear glasses.
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Post by mastertech on Feb 27, 2015 13:11:10 GMT -5
The cap above the regulator could also be a possibility but less likely.
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Post by justgreg on Feb 27, 2015 14:49:12 GMT -5
Sounds like a fun test. Too bad my laser thermometer is at work. A thermal camera would be a great tool too. On with the testing!
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Post by justgreg on Feb 27, 2015 18:24:14 GMT -5
The diode cooks the flux right off within seconds. The cap and reg are fine. Interesting test trick Mac....guess that's why you get the big bucks.  Where to next with this puppy? |
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Post by mastertech on Feb 27, 2015 20:27:18 GMT -5
The diode cooks the flux right off within seconds. The cap and reg are fine. Interesting test trick Mac....guess that's why you get the big bucks. Where to next with this puppy? That is one of my secret tests and I was debating on whether to post it or not, lol. Next is remove that diode. Then see if you still have that short from the fuse to ground with DMM on diode scale. No power. |
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Post by mastertech on Feb 27, 2015 20:28:11 GMT -5
Oh, try to see if there are any numbers or letters on that diode before you try to remove it, just in case.
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Post by justgreg on Feb 27, 2015 21:00:38 GMT -5
Well I appreciate you sharing it just as much as the rest of the world must be. lol
I did some research on the diode yesterday and it came back as a zener diode. The pix I took are better than my eyeballs (until my just ordered digital magnifying cam comes in!). I zoomed in on pic 3 (the best quality) and the only markings I can see is a blue band and a black thinner band. The black band could be from some internal construction. No numbers tho.
I'll post my erm, post-removal results.
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Post by mastertech on Feb 27, 2015 21:05:28 GMT -5
Well I appreciate you sharing it just as much as the rest of the world must be. lol I did some research on the diode yesterday and it came back as a zener diode. The pix I took are better than my eyeballs (until my just ordered digital magnifying cam comes in!). I zoomed in on pic 3 (the best quality) and the only markings I can see is a blue band and a black thinner band. The black band could be from some internal construction. No numbers tho. I'll post my erm, post-removal results. Yes, I already know it is a zener and I already know its app. voltage. We will make final decisions after your testing is complete. |
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Post by justgreg on Feb 27, 2015 21:38:32 GMT -5
Well shucks. I lifted the opposite end that's furthest from the mains...still a short. Dang it. I the power switch and it's functioning correctly so no easy fix there.
Question on SMD caps. I expect to get a tone from SMD filters (L) but should I get a tone from SMD caps? I started the pain staking job of checking all the SMD caps and found one (so far) that produces a tone across it's poles. And...when you test a couple hundred of the little buggers how do you keep track of the ones you've done? Wish I had a fine point white paint pen.
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Post by mastertech on Feb 27, 2015 21:52:10 GMT -5
What, are you writing in greek? Rewrite that paragraph so i can understand what you are trying to say.  |
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Post by justgreg on Feb 27, 2015 22:28:06 GMT -5
hahahahaha Sorry about that. When one doesn't know the language you either talk loud...or make up words.
I assume you understood the first part? With one end of the diode lifted I still get a short at the pad it was formerly soldered to Conversely when I tested from the raised end of the diode I got a reading of around .965 on cap scale.
The next part was a question about SMD caps. Should I ever get a continuity tone when testing across a cap? With an electrolytic it indicates an internal short. With a ceramic SMD I don't know if I can get a continuity tone by design of the cap, or if it indicates the cap is internally shorted like a bad electrolytic.
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Post by mastertech on Feb 27, 2015 22:47:21 GMT -5
You cannot test caps in circuit with a DMM. Only with an ESR meter. On the attached picture you see 4 through pins in the red circle. I need you to flip the board, find those 4 pins and snap a picture for me to see.  |
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Where to next with this puppy?
