Replacement power supply for Apple Cinema Display

Submitted by Pixel Chimp on Tue, 18/09/2012 - 15:39

NB: Photos copyright Eroni De Oliveira

A reader sent me some information on replacing the Apple power supply for the Cinema Display. He realised that a 24V 'LED Strip' power supply should meet the power requirements for the display.

The power supplies sell for around $20 which is a considerable saving compared to the Apple version around $100 to $200 (depending on usage). He was in the process of testing 2 'dead' displays and was able to exchange parts between them to diagnose the problem for each display…

I ended up fixing one of the monitors by switching CCFLs between them, which confirms my belief that the most common problem among these older units, is related to the backlight bulbs. The other monitor has a cracked LCD display.

Like any fluorescent lamp, as they get old, and darkens it's extremities, their current consumption changes, triggering protection circuits in the ballast board and/or the logic board, as well as in the external power supply itself. Remember that these bulbs work with high voltage (around 420 Volts) and any small current variation at that level causes a much higher one at lower level, hence the need for protection circuits despite having a 3 Amp fuse at the ballast board. That explains why, sometimes, a more powerful power supply is able to correct it (temporarily nevertheless).

Another issue has to do with the high cost of the original power supplies been, most of times, twice the price of a defective monitor. I decided to use an alternative power supply that cost around $ 20.00 and are very stable and ripple free. They are designed to power LED strips, with an output of 24 Volts, 5 Amps (about 120 Watts). They have others with different specs also. The output voltage can be "fine tuned" to precisely 24.5 Volts; there is a control for that purpose.

The connection is simple: the shield (from the monitor) is grounded along with the ground from the AC line (green wire). The red, from the monitor, goes to the positive and the black to the negative. The "control/protection" from the monitor (center thin wire) I left disconnected. I trust that the 3 Amps. (on the ballast board) should blow, in case the bulbs get really bad.

Ebay LED Power Supply and Alternative Ebay supplies

– Eroni De Oliveira.

The pictures are self explanatory, cut off the Apple power connector from the display and wire the correct outputs from the supply.

It certainly seems like a good solution. With a simple case added to the supply it should keep running for another few years just think about the heat dissipation if you do choose to put it in a case.

Thanks for the info Eroni, I envy your workshop :^)

Comments

Alternative PSU for 20" and 23" ACD

Submitted by Anonymous on Fri, 28/09/2012 - 22:20.

Good job, Eroni. As to myself, I've used an old Powerbook 65W PSU for testing my 20" ACD.

And yes, nice workshop you have there!

No luck though, Q1 on the motherboard itself is blown. It is an SMD transistor, and nobody seems to be able to identify it...

PS for 30" model

Submitted by Anonymous on Wed, 31/10/2012 - 12:10.

The 30" cinema display uses a 150W power supply. Still 24.5v but also 6.1A. Do you think the 2nd power supply, "Universal Regulated Switching AC in DC out Power Supply LED)" will work on this? It shows a range of amps, 2a, 3a, 5a, and 10A. Though I can tell how to adjusting the voltage works in the picture, its not clear to me how amps is set/detmermined for output. 5A would be too little, would 10A be too much?

Thanks,

--David

It might be OK…

Submitted by Pixel Chimp on Wed, 31/10/2012 - 15:43.

I'm not entirely sure, but I think it should be set to 10A, then the display will draw the 6A it needs. The power supply shouldn't get overloaded since it is running below the 10A setting but there is a risk that the supply could overload the display if the display draws too much current.

FWIW the display Eroni fixed was a 23" model that originally runs from a 90W supply, he used a 5A (about 120W) supply. He does mention that the as the backlights fail they can draw more current so if they start to go bad there is the possibiity blowing the fuse on backlight board.

I will ping Eroni to see if he can add anything.

A bit more info

Submitted by Pixel Chimp on Thu, 01/11/2012 - 02:12.

Eroni kindly replied with some more information...

Hi Drew.

You are absolutely right. As long as the voltage is correct and the current (amps) capacity of the power supply is HIGHER than the consumption (demand), everything should be all right, assuming the monitor has no other problems. Take as an example a car battery that has to provide, let's say 500 Amps to turn over the engine, when starting. The same battery will light a 1 Amp bulb without damaging it, because it's voltage is constant.

In the case of David, if his monitor stopped working with it's original P.S. and is able to function with a more powerful one, I would think it is consuming more current than it's suppose to. Again, my suspicion, in this case, would be the aging backlight lamps (CCFL). Granted, he may get few more hours out of these lamps but still is, in my opinion, a temporary fix.

Another issue is, as we talked before, is the elimination of that center wire from the monitor, which I believe to be a control line that shuts down the power supply, when the consumption becomes excessive. That is why some people disconnect that wire with a piece of paper and get them going for a while longer, remember ?.

If the lamps get so bad and the current reaches high values, still there is that 3 Amps fuse in the ballast board as the last resort protection agains serious damage.

Take care of yourself, and good luck to David. Remind him to observe correct polarity.

Eroni

I hope that helps David, please create an account if you reply, I may be able to email you more info. I'd guess the 30" display has a higher rated fuse on the inverter board for the CCFLs.

Just did this for a 30" Apple Cinema Display

Submitted by Anonymous on Sun, 10/02/2013 - 22:42.

Hey guys, great info thanks so much.

I just did this with an Apple Cinema Display 30". I bought a 24V 150w 6.5A power supply off ebay. This one: http://www.ebay.com/itm/250876072121

Since the ACD was 6.1A I figure that's close enough without allowing the current too high.

I am by no means skilled with wiring but Eroni's instructions were simple and easy. $24 total. I can provide a pic if you want!

Joel

Hey that's great Joel. I'll

Submitted by Pixel Chimp on Mon, 11/02/2013 - 00:04.

Hey that's great Joel.

I'll add the pic to the post if you want to send it. Try the contact form & I'll get back to you.

It's good to hear others have resurrected these displays :)

More options?

Submitted by Anonymous on Thu, 11/04/2013 - 17:07.

Sorry to bump an older post, but I was inspired myself by this post and had a possible contribution/question. Would something like this device work as well for the 23 inch model?

http://www.bestofferbuy.com/120W-Universal-Digital-Power-SupplyAdaptor-for-Laptops-12V24V-DC-Ou-p-64964.html?currency=USD&utm_source=gbase&utm_medium=cse&utm_campaign=gbase_usa&gclid=CIrKrtGLw7YCFcFAMgodGjEAJQ

Looks like it can offer a max of 24v/5a from the product description. It’s about 10$ more than the ebay unit but I feel it offers more aesthetics for the extra money. I may order one up and test it out on my 23 inch and post the results but thought I would ask if there may be any glaring downsides to using this over the ebay PS?

Thanks again for this informative post!

I'd expect that to

Submitted by Pixel Chimp on Thu, 11/04/2013 - 18:01.

I'd expect that to work.

It has 24V/120W output that should provide the 90W that the 23" display needs. I'd guess it will warm up since it will be operating near the upper end of it's spec, but it should work.

I think the LED power supplies have a potentiometer to change the voltage, but that supply probably has selector switches, so you may find the voltage is not as adjustable. Just make sure it outputs a clean, stable 24V for the display and check it doesn't sag too low as the monitor starts up (ideally no noticeable dip in voltage at all unless you have an oscilloscope to measure precisely).

The casing looks like it is all plastic, so you can't easily ground the display's power cable shielding. I believe you can hook the shield up to the ground inside the power supply, but that would give you another wire to run to the display. If you leave the shielding ungrounded you may see noise on the display, or the display could cause interference to other items (I think). I'm really unsure how much this will be an issue, and it's unclear how the supply can be earthed if it only has a 2 pin EU mains input (I know much about the EU/US system). It may support earthed input judging by the photos.

Ideally the PSU would run with an earth/ ground, since the display is metal :)