Can I improvise a power supply for a strange monitor?
March 29, 2010 11:41 AM   Subscribe

Can I improvise a power supply for a mysterious LCD monitor? A sticker on the back gives the power requirements, but the plug type is strange.

I have a 17" touch-screen LCD monitor with no power supply. I believe it was formerly part of a POS system. It's very heavy for its size, and is totally nondescript except for a label on the back with some serial numbers and the power requirements. I've had no success finding anything out about it with internet searches.

It wants 12 volts at 3 amps. The power cable (permanently attached) has a plug type I've never seen before: male, 4 pins, arranged in a rectangular formation in the center of a 1/2" circular plug. If I track down some power supply for something else that puts out the right voltage and amperage, can I somehow wire it to this plug? Why are there 4 pins and not 2 or 3? How can I find out how they're wired? I'm not afraid of making a project out of it, as I'd really like to get this thing working (assuming it works at all).
posted by Maximian to Computers & Internet (7 answers total)
Photos will help.
posted by griphus at 11:42 AM on March 29, 2010

My camera is having some problems, but here's a blurry photo of the plug.
posted by Maximian at 11:55 AM on March 29, 2010

Does it look like this?
posted by zamboni at 11:56 AM on March 29, 2010

Since it says 12V 3A, you can guess that it's probably not a dual power supply. That's handy, it means your 4 pin connection is probably really a two pin connection.

You can open the display. Inside, you'll be able to see how the power is connected. On the circuit board, the ground of the plug (the minus of the incoming power) will be connected to screws to the chassis of the display. Or you can test with a continuity meter from the negative leg of a capacitor (the legs are labeled negative and positive). Once you find either a negative or positive pin, you can hook up your power supply.

I know these instructions aren't particularly clear, but I've done this several times with unknown electronics using this method. Just open the device, find a ground or negative pin, and check continuity between that and the connector of interest. The other pin will most likely be positive. Check it briefly with power to see if you get any activity. If it works, cheers!
posted by fake at 12:06 PM on March 29, 2010

Fortunately for you, 12V power supplies are incredibly abundant. If it's at all helpful, 3A at 12V translates to 36 watts.

Unfortunately, it's still a bit too much power to draw from a single +12V rail of an ATX power supply. Wikipedia claims those are limited to ~20A per rail, although I've seen plenty of POS touchscreens wired in this manner. YMMV.

As for the 4 pins, there are a few possibilities:
*One or two could be unwired
*There are 2 pairs connected to 2 sources. Apple's MagSafe connector uses such a design.
*Two are used for power, and the other two for the touchscreen interface or some sort of other communication link.

Unfortunately, you risk frying the screen if you connect them improperly. You might be able to crack the monitor open and determine the correct pinout from the markings on the circuit boards inside.
posted by schmod at 12:19 PM on March 29, 2010

If you open the monitor, look for serial numbers on any circuit boards you find inside. I've found an amazing wealth of information by feeding cryptic part numbers from circuit boards and the like into Google.

Standard Warning: Be careful of capacitors in there. It's LCD so there shouldn't be anything too big and sounds like it's been a while since it's been plugged in but now you can't say I didn't warn you.
posted by Kid Charlemagne at 12:29 PM on March 29, 2010

A dedicated ATX power supply will be crazy overkill for this job. However, you might as well plug in to your main computers power supply using one of the drive connectors (called a molex connector on that wiki link - yellow is 12V, black in ground). Just run a wire through a hole in the case (like a PCI slot cover, or whatever).
posted by Chuckles at 3:22 PM on March 29, 2010

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