Overheated power block

ben7 · Aug 30, 2010

I've got a cheap power block that overheated, and bit the dust! Funny thing is, it actually has a regulation circuit to regulate +5.2 volts. Anyway, The transformer's primary is open(thermal fuse blew). It seems to be a small transformer for a 500mA rating, don't you think! I think the super thick heat-sink/chunk'o-metal is not suitible for the transistor in the regulator circuit, and believe it or not, the transistor has no brand/company logo on it! Stuff like this is getting more common nowadays.
What a shame!

Sceadwian · Aug 31, 2010

What are you talking about? That's always been common =) Non-marked is at least better than super vague in house markings that make no sense unless you know the building it came from and the guy that marked it =>. For 500ma nothing seems wrong with the transformer size to me, and by the way what you're calling the transistor is probably actually the IC regulator.

Any idea why the primaries thermal fuse blew? It's uncommon for these kinds of supplies to fail, although it might not be short circuit or overload protected it doesn't make sense that the primary blew, unless the whole mass heated up enough to justify blowing the primary, which would mean the regulator isn't over current or thermally protected.

mramos1 · Sep 1, 2010

I would think about any 8-12 volts ac transformer (500ma) would get you back up and running. I can see the bridge rectifier, filter cap, regulator, etc. So as long as the regulator is not blown should not be hard to get it back online. What was the 5.2VDC running?

ben7 · Sep 1, 2010

Sceadwian said:
What are you talking about? That's always been common =) Non-marked is at least better than super vague in house markings that make no sense unless you know the building it came from and the guy that marked it =>. For 500ma nothing seems wrong with the transformer size to me, and by the way what you're calling the transistor is probably actually the IC regulator.

Any idea why the primaries thermal fuse blew? It's uncommon for these kinds of supplies to fail, although it might not be short circuit or overload protected it doesn't make sense that the primary blew, unless the whole mass heated up enough to justify blowing the primary, which would mean the regulator isn't over current or thermally protected.

I am not exactly sure why the thermal fuse blew...there seems to be a zener/resistor regulator circuit that feeds voltage to the base of the transistor, which is marked D882. So it isn't regulated very well...cheap china crap. It is possilble that it there could have been overloaded, or a winding in the transformer shorted out. I will cut apart the transformer windings eventually. It says on the case it was made by DVE in china.

ben7 · Sep 1, 2010

mramos1 said:
I would think about any 8-12 volts ac transformer (500ma) would get you back up and running. I can see the bridge rectifier, filter cap, regulator, etc. So as long as the regulator is not blown should not be hard to get it back online. What was the 5.2VDC running?

I have already replaced it with a 5 volt power supply. The device it powered was a rechargeable, electronic calender for another family member. It took a little longer to charge the Lipo battery but it was an easy fix.

One thing to note is the capacitor (105C rated) isn't swollen from the heat.

Overheated power block

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