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How to test computer screen power adaptor for failure?

I haven't used my Wacom Cintiq 24HD screen in a few weeks and it's not working properly.

After disconnecting the power supply from the wall socket for a few minutes and re-connecting at most I get some flickers of the screen, followed  quickly by turning off entirely. If the adaptor keeps power connected then the screen won't do anything, and so I figured it should be the power adaptor that could be failing.

I'm really not knowledgeable with electricity so I thought I could ask for some help here:

- The power supply adapter has a light that is faintly lit while connected;
- It reads *Output: 24V =-=-= 5A* on the back
- The end terminal is similar to a Mini DIN Connector type connector, round with 4 pins that are arranged in a perfect square, but not as standart I think.

How can I check if the power supply is working properly with a multimeter like the one in  the picture?
 
I did try setting it almost like the photo, one step to the right (20 V, black on COM and red on VΩmA), and when I touch the pins inside the connector I get a spark out of it. Pressing the black tip as well against the outside ring always result in a spark from the red tip and values reading erratic on the multimeter's screen. Can this be used to make any sense of this?

I've looked for power supply replacements and they're looking to be very expensive to get directly from Wacom. One final question: if it is failing, could I try to get some alternative solution working here? I don't know, using an universal adaptor and request soldering a more common connector to this Wacom proprietary one's tip?

Thank you in advance


Picture of How to test computer screen power adaptor for failure?
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The ring on the outside of that connector is a pin too.

So there are 5 pins there, which is 3 more than the minimum number needed, which is 2 for a supply with 2 rails, namely +24 VDC and ground = 0 V.

Which of those pins are connected to what, well, that's up to you to discover. You're in a better position to discover which wire goes where, than are the people on this forum who can only imagine your power brick, but can't see it or touch it.

If you see sparks, that means you're doing it wrong; i.e. your probe tip is touching two pins at once, or touching a pin and the outside ring at the same time, which is the same thing, because the outside ring is a pin too.

Also, I think DU mentioned this, but it bears repeating. If you're looking for 24 volts DC, and the scale is set to 20, you've got the scale set too low. Set it to 200 VDC.

It may take some dexterity to measure the voltages on those connector pins, since they're all close together like that.

Another approach is cut open the cord, and poke something into the wires, like push-pin, or thumbtacks or something like that, and make the voltage measurement that way.

If you want to test the ability of your brick to supply current, that will almost certainly involve some surgery on the cord. The same is true if you want to measure the current drawn by the monitor, since the ammeter needs to go in series with the power supply.

So. Yeah. If you're contemplating throwing all this junk away anyway, why not cut open the cord and see what's inside it?

acn (author)  Jack A Lopez1 year ago

Thank you very much for your time spent writing this, it helped me understand how to properly check if the power adapter was ok.

I read somewhere else a suggestion to leave the adapter rest disconnected for a long period of time, and I was waiting to test it afterwards. These adapters (original) tend to heat up quite a lot, maybe that's the issue.

I found the two inner pins from which I could read the output voltage, and it fluctuated around 24 V on both, while closing the circuit with the outside ring. After this I connected the monitor and this time it turned on and worked just fine. The sparks were in fact due to my ignorance and touching other pins.

I guess the most likely scenario is that the adapter could be near failing, so I'll have a look on replacing it, though I know it will be expensive (150 euros, or around 165 USD).

Thanks again for your help, at least I got to verify what I wanted.

Cheers!

-max-1 year ago

Before you do anything always look to see if you can RMA it and see what warranty it has. Sounds like an expensive bit of kit, I would expect it to have some sort of 1 or 3 year warranty. But if that proves fruitless, You could investigate the power supply. First rule of troubleshooting electronics is "thou thalt test voltages!"

To ensure the power supply is working, you may need to do a little research, figure out the pinout, all nominal voltage rails with rated maximum currents, and go from there testing things. It's possible you read no voltage, or only something like 3.3 or 5V and no 24V, because an "enable" pin has not been connected.

You're multimeter is absolute garbage, and you probably fried it if you measured a 24V rail with a 20V multimeter setting (that is the absolute maximum voltage for that range.). A good way to tell cheap meters from the turds is to see if they have that NPN / PNP transistor tester. None of the good meters have that, for good reason. So get a decent one. Making voltage measurements with a multimeter should never result in sparking, unless you had it set to amps mistakingly. Also sparking would seem to indicate either the power supply is alive and kicking, or that something went horribly wrong and caused excessive voltages to appear on the output. (very doubtful considering that it is probably a top quality tablet and power supply)

If you already know the thing should give 24V out - wouldn't it be logical to assume that 20V as the setting on the meter can't be enough to measure it?
And if all you create is sparks than you are not measuring at all - you are creating short cuts that can totally damage the power supply.
If you want to measure voltage you use the setting that is high enough for the suspected voltage and if unknown start from the highest setting.
Assuming you did not kill the power supply I would suspect your monitor is toast, maybe dead capacitors on the main board, faulty backlight...
If you want to test the power supply please give it to someone who actually knows what he is doing.