Choke/coil/inductor: replacing or measuring

[tmcw]

I was troubleshooting a balance, and found that the power supply, a wall-wart block converting 230v AC to 9v DC, was dead.

I managed to crack the casing cleanly open, and found that the choke had one of it's 2 legs broken from it's soldering point. The choke doesn't have a base, it's just the donut-ring with the copper wire wound around it, and two wires emerging from the bottom, which go through the circuit board, and soldered directly to it. The wires are quite thin, and the wall-wart looks like it took a knock, hence probably why the wire broke. The choke does have a covering of heat-shrink, and I can just see "25oC VW" on the heat shrink, no other markings. There was no glue holding the choke to the board either.

I haven't tried to solder the choke back on again, the broken wire isn't long enough to go through the board anymore, so I'll need to solder a short bit of wire to extend it, but before I attempt that, thought I'd ask a couple of questions first.

While I have the choke off, is there anyway of taking a measurement off it to determine its "value" or specification? I'm conscious that if I start messing with it, trying to solder a bit of wire to the leg, I might damage it, so if I need a replacement, I'll know what I need.

Also, there are a couple of Fullcon 85oC GR caps on the board; should I replace them while it's open?

[999999999]

Re: Choke/coil/inductor: replacing or measuring

You can probably get away with just cutting the heatshrink tubing off, inspecting the windings to make sure they don't "look" like the enamel is burnt off to make any shorts, then unwind a winding or two to get enough length to strip and solder it back to the board.

Once you've done that if you have no suitable replacement heatshrink tubing, fold a piece of cardboard around it and tack the component and cardboard down with silicone caulking or epoxy or whatever you have that's reasonably heat resistant.

The high (voltage) side capacitor usually lasts a lot longer than the low side output filter cap so if you have a spare cap for the output position I'd replace it.

Then again, small current 9V DC wall warts aren't very expensive. While it is an exercise in learning failure and repair methods, it is often just as time effective to just buy a new one if you don't have a spare sitting in an drawer somewhere or don't have a charity shop (like Goodwill in the U.S.) that sells used electronics dirt cheap.

Measurement requires an oscilloscope, inductance meter, or signal generator whose frequency is used to calculate inductance. Measuring it won't do much for you. If it's shorting out then the measurement will be off. If it's not then you don't need a replacement.

Just take your time and undo a winding and you should do Okay.