[Stephonovich]

I've got a Sony DC power adaptor; standard for the Discman. 4.5v out, black, with blue text, yadda yadda. Anyway, it recently died on me. I took my DMM out and tested first the plug, tried cleaning it, then cut the wires and tested them. No power. No obvious breaks or cuts in the wire anywhere. Any chance that this can be repaired, or am I better off buying a new one? eBay has them pretty cheap I see...

Heh heh, new smilies...

(-:Stephonovich

 

[kevin gilmore]

Sometimes they overheat, or the safety fuse inside
open due to various reasons.

You need a good bench vise. You use the vise to apply
pressure along the seal between the two halfs, and
you may have to do it a couple of times to get the thing
to open all the way.

Then you can figure out what is wrong.

The safety fuse is usually part of the transformer, and
when you find it you can short it out...

 

[PeterR]

Quote:

Originally posted by kevin gilmore The safety fuse is usually part of the transformer, and when you find it you can short it out...

You sure this is good advice?
Fuses aren't there to annoy you, but to protect you and your property. If a fuse has blown, assume it may have done so for a reason. Shorting the fuse won't fix the real cause of the failure, but now there won't be a fuse anymore to save the day...

 

[Stephonovich]

Actually, we used the almighty Dremel to open it up...

I think it must have been the wire connecting to the transformer inside. I checked all the solder joints and whatnot, none of them were bad. So I re-soldered all the wires back, secured them, and duct taped the whole mess together. Works fine now.

Also, when measuring the voltage out of the wires from the transformer, it's 6.95 volts! All we can think is that there's a resistor in the plug...

(-:Stephonovich

 

[tangent]

Quote:

Also, when measuring the voltage out of the wires from the transformer, it's 6.95 volts! All we can think is that there's a resistor in the plug...

This is normal with an unregulated power supply. Their output voltage drops to the rated value at the rated current.

 

[Stephonovich]

So, you mean at 500 mA, (it's rated output) it drops to 4.5v?

(-:Stephonovich

 

[tangent]

Roughly, yes. But because it's unregulated, you can't count on any particular voltage without specifying conditions precisely. When you use an unregulated power supply, you take this into account, and build your device either so that it has its own internal regulation, or so that it will cope with different supply voltages.