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| Christmas tree lights 24v or 26 power supply |
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| AVGresponding:
Big Clive has loads of videos on fault-finding and repairing simple switchers like this. Might be worth watching a few. Usual suspects are failed electrolytic caps, sometimes they take out surrounding components unfortunately. Shorted windings on the trafo are less common but not impossible; with no power being drawn, the fusible resistor may well have blown. If you decide to source a replacement supply, I wouldn't worry too much about exactly matching the output voltage, these things aren't precision devices and +/-10% should cause no issues, the lower the better (within reason) as the LEDs are likely being overdriven anyway, so dropping the supply voltage to 20 or 22 will probably make them last ten times as long, for very little difference in brightness. Remember to check the 400V caps are discharged before you stick your fingies on 'em! |
| madires:
... shorted diode on the secondary side or shorted bridge rectifier. |
| MrMobodies:
Thanks. The green 4.7uf cap measuring 4.59uf. Tracing from the live terminal to BD1, the resistor in the middle doesn't seem to measure anything. I think that resistor might have sometime to do with it. Just noticed what looks like a crack in the middle. Left: Red Black Black Golden Just found: https://www.make-it.ca/resistor-color-code-calculator/ So that will be: 20 Ohms +/- 5% tollerance. So something else is likely to have failed to cause that resistor to break. Just noticed something. F1 next the resistor. So that is acting like a fuse? Took a look closer RF1 and I guessed it, a fusible resistor: Another crack on the side. Apart from the color coding it seems to looks just like the one in this link: https://www.elprocus.com/fusible-resistor/ No signs of overheating so maybe it shorted out somewhere. Thanks for your help. I'll see if I can order another one and see what happens. |
| Zero999:
My bet is U1, which contains the switching transistor. |
| MrMobodies:
If the power supply works again then the problem was likely triggered outside from the cables or lights and this could be a waste of time but interesting. What I forgot to mention was that they wired it around a tree from a window. Now thinking about this I feel a bit stupid that I didn't take that into consideration. They wanted a replacement power supply but that could blow too in the same way. When I meet them next time I'll ask if they can take the down the lights and give them to me to test. |
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