Why is my homemade boombox not getting power?

May 2, 2009 2:17 PM

Hooking up old Sony car stereo as a standalone boombox - what am I doing wrong? Followed Metafilter advice, but my wiring is wonky.

Posted this question about converting a car stereo into a homemade boombox awhile back. Got good advice, so here's my setup.

Bought a 12V 500mA AC adapter from Radio Shack and snipped off the end. Connected the wire with writing on it (it says: 22AWG 300V CHICK YUET AWM -LF-) to the YELLOW wire from the wiring harness. Sony manual says the Yellow is Power (constant). Connected other adapter wire to RED. Manual says red is Power (ignition). Black (ground) wire from harness is connected to a screw w.rubber washer. Entire assembly is in a wooden box.

No power. Changed 10A fuse. Even swapped the Red/Yellow. No luck.

The manual states the stereo power (when in a car) as 12V DC car battery (negative earth).

So... appealing again to your smarts. Is there something obvious I'm doing wrong, or is this radio shot?

posted by smelvis to sports, hobbies, & recreation (12 comments total)

Both the Power (constant) and Power (ignition) wires should connect to the positive wire from the AC adapter. The ground wire should connect to the negative wire on the AC adapter. I'm not 100% sure on which wire from the AC adapter will be positive and which one will be negative. I'd check with a multimeter to make sure. Also, 500mA isn't a whole lot to be powering a car stereo from. I doubt you'd be able to play things very loud at all without blowing out the AC adapter.
posted by zsazsa at 2:26 PM on May 2

Can you supply more information about the adaptor? Just it only convert to 12V AC? Or does it convert to 12V DC, as that is what is required by the radio.

Also, echoing the first post - the yellow (in the car) is permanent power to stop you losing your presets when the car is off, the red is so that you can turn your stereo on when the car is on (and so it goes off when the car does). Both should be attached to the positive side of the adaptor for this to work, with the black wire to the negative terminal.
posted by Brockles at 2:32 PM on May 2

I kinda doubt 500mA is going to be enough to power the radio.
posted by gjc at 2:37 PM on May 2

zsazsa is right on all counts. Half an amp isn't much to run a stereo on. Your stereo has a 10A fuse, after all -- this transformer is way too small.

That aside...

When the stereo is in a car, the yellow wire is what keeps the digital clock running, the station presets in memory, etc. The red wire (ignition) is the one that provides power to actually operate the stereo. You say the ground wire is connected to a screw, but what's the screw screwed into? In any case, it should be connected to the negative wire from the transformer.
posted by jon1270 at 2:38 PM on May 2

I missed the spec of the adaptor, but agree it isn't enough. Something like this is more the style of box you need, although I am sure there are cheaper ones out there than that. The one you have is of mobile phone level power consumption, not one that will power 4 speakers to decent volume - that takes a fair bit of juice (hence the 10A fuse).

Once your wiring is sorted out, my bet is you will still need a bigger power supply.
posted by Brockles at 2:48 PM on May 2

Here is the adapter. It is a 500mA AC to 12VDC Adapter. The Radio Shack guy recommended this one, and when I went back today with the whole wiring carcass, the other clerk confirmed (but I think they were more interested in selling phones).

To confirm - the positive side of the adapter is the wire without wiring, correct?
posted by smelvis at 3:08 PM on May 2

There is a lot of guff out there in a 'car stereo current usage' search to get through to find any sense, but the link here suggests the guy at Radio Shack is well out of whack with recommending that power adaptor.

Any device that has a 10A fuse rarely usually operates at such a tiny fraction of that number. I'd be surprised if you have enough power there to run the radio beyond a slightly audible volume. A power supply at least as large as the fuse rating will prevent any potential damage to over-working the adaptor.

To confirm - the positive side of the adapter is the wire without wiring, correct?

That doesn't make any sense to me. Can you try explaining again? Either way, I'd be inclined to take that power supply back and get a more powerful one, so don't modify it in any way.
posted by Brockles at 3:23 PM on May 2

To confirm - the positive side of the adapter is the wire without WRITING. (not 'wiring', my bad).

It looks like I bought the wrong adapter, but the tip is snipped off, so no return. I've already sunk a few bucks into this "recycle" project, so I'm a bit disheartened about this whole thing. That being said, I'm determined to make this work and have the best homemade/fugly boombox on the block.
posted by smelvis at 3:29 PM on May 2

Well. What does the writing say? There's no way to make a generalised assumption - the negative usually has a ridge running down it (not the one connecting it to the other wire) but it really depends on the make of the adaptor.

Do you not have a voltmeter to test it and see?
posted by Brockles at 3:55 PM on May 2

Usually the positive side is the side with writing.
posted by gjc at 7:46 PM on May 2

Once you get this thing all jimmied up and working, check for hotness. It may get heated due to improper wiring and red-neck setup and all.
posted by P.o.B. at 4:52 AM on May 3

There is no way that's enough current to drive the car stereo. Your adapter can supply 6 watts of power. There is no way that's enough, and when the stereo "asks for" much more the output voltage is going to drop to practically zero. Consumer wall wart adapters don't normally supply the kind of power you need, which is probably (at least) going to require 10x the current. You can probably get this kind of juice from ganging together several of the 12v outputs of an ATX computer power supply.
posted by range at 12:00 PM on May 3