Electronics inquiry: AC adapter faults

[Jace-BeOS]

I hope this is the right place to ask this... I posted it over at GearSlutz and so far no one has replied.

I'm not an electronics person but I'm trying to learn some things.

I have an AC adapter that's rated 12 volts, 1.8 amps. The device it's for won't function. The adapter sometimes ticks when plugged in by itself (no device connected), but it mostly just seems to whine. I assumed it was dead and ordered a replacement.

However: it occurred to me to test its output with a multimeter. It reports a little more than the rated 12 volts. When I plug it in to the device, the device powers just for a fraction of a second (LEDs flick on and off) and the AC adapter whine goes silent.

I'm presuming this means the adapter cannot supply the amperage the device pulls, but what I've read on the web about under-amperage cases is that the device will pull more voltage to compensate (??). Maybe it just doesn't deliver current at all?

Once I disconnect the device from the AC adapter, the whine returns and the voltage again tests as before (just above 12 volts).

I guess my question to the experts here is: is there any other way to test the adapter by itself?

What I've read elsewhere online suggests that a multimeter cannot test the amperage of an adapter because it's not part of the circuit. Trying to make it part of the curcuit is problematic and probably would result in busting fuses and learning nothing. Anyway, I don't want to disassemble the device it is supposed to power in order to find an internal place to tap into the circuit with the multimeter. Does some kind of an AC adapter testing device exist for people who do this stuff professionally?

Until I get my replacement AC adapter, I cannot be certain the fault is the adaptor itself, though the noises it makes seem to make that likely (it never made these noises before).

I hate waste. If it turns out to be faulty, do people ever repair these things? It seems very difficult to unseal them, though of course there are YouTube videos showing people doing just that (from dissolving the glue with petrol, to prying or even busting them open forcibly).

[justin3am]

If it's an unregulated PSU, then it's normal to measure a higher voltage than spec'd, when the PSU isn't under load.
If the PSU whines, there could be a failing part. Is the output AC or DC?
If you disassemble the device in question, you should be able to probe the leads of the barrel connector, no need to bust any fuses or anything like that. I would say, if it looks like the device is powering up for a moment, it's more likely that the problem is in the PSU but I can't say that definitively. There may be a capacitor that needs to be replaced on the device side.

[Jace-BeOS]

If it's an unregulated PSU, then it's normal to measure a higher voltage than spec'd, when the PSU isn't under load.
If the PSU whines, there could be a failing part. Is the output AC or DC?

DC.

If you disassemble the device in question, you should be able to probe the leads of the barrel connector, no need to bust any fuses or anything like that.

I considered that. I'm not looking forward to disassembly. Hopefully the replacement power adapter will solve the problem.

I would say, if it looks like the device is powering up for a moment, it's more likely that the problem is in the PSU but I can't say that definitively. There may be a capacitor that needs to be replaced on the device side.

Hopefully not.

Do people ever repair power adapters or only send them to e-waste recyclers as garbage?

[justin3am]

Well it depends on the power adapter. For a 12v DC 2A, off-the-shelf wall wart, I would just get a new one. You double-checked the polarity of the connector before ordering the replacement, right?
If it was something more scarce, I might repair it or build a replacement on perf board. It's handy to keep one of those variable voltage adapters around, that have a bunch of different connector types.

Some of those wall warts or line lumps aren't designed to be disassembled but if it's not working now, I'd say knock yourself out. The worst that could happen is it stays broken but you learn something. Just be aware, you are dealing with high-voltage and enough current to kill you. Be very careful.

I try to keep the e-waste to a minimum as well but so much these days is designed to be disposable and not easily reparable. At one point I was like "I'm not going to buy anything I can't repair myself, from now on!" That didn't work out for long.

[Jace-BeOS]

Yeah, I'm not remotely competent in electronics repair. I've managed to (near-accidentally) reattach a surface-mounted capacitor popped off a PowerMac motherboard once. Luck.

I just hate waste.

Edit: Oh and yes, I checked the tip polarity.