Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

[Chungalin]

A good Apple LCD monitor, "Cinema HD Display", 23", model A1082. Doesn't power up. The customer says that has tried with another power supply and it works, so it's a PSU fault. It's an A1097 power brick. Seems expensive enough to try a repair.

It outputs 24V fine with no load, but as soon as you connect the monitor, the voltage starts to drop and rise (up to the nominal 24V) in a 1 second cycle. Monitor's led is off all the time.

I open it with hammer and flat screwdriver (much less destructive than you're thinking, believe me!!). Everything looks fine inside, no overheats, no blows, no bulging, good quality components... No info anywhere in the net, like I'm the first one trying to fix one.

I don't know what to do. Then I see that it has a polyester film capacitor 22nF 630V ("223J 630V" marking) in parallel with the primary electrolytic filter (150uF/450V). This film capacitor is exactly the same guy than the one from Yamaha receivers and sound bars that fail so nicely and that have been spotted years ago.

So, nothing to lose, I change it and... it works!! I'll test it more thoroughly to be sure, but I couldn't get it to work not a single time before, so, what should I think?

[budm]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Can we see this cap and how it is really connected in parallel with the main filter cap to have affect the operation of the circuit? it sounds more likely to be connected to one end of the main switching transformer primary winding and part of the primary drive circuit.

[Chungalin]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

The PCB is densely populated and double sided, so it’s very difficult to see the tracks on the component side when the components are mounted. I’ve rechecked it with multimeter and the film capacitor is in parallel with the primary HV filter capacitor. Don’t ask me why. I checked the primary voltage while the power supply was failing and the 320V DC were there (230V AC mains here), so apparently there wasn’t anything wrong.

The capacitor is almost identical to the one that fails on Yamaha receivers (several models affected), pictures here:

https://www.avforums.com/threads/yam...oblem.1533016/

The only difference is that the one from Apple’s power supply has tolerance J (5%) and Yamaha’s is K (10%). I’ve replaced it with a K.

I remember that I knew about this failure two years ago through a Yamaha’s service bulletin. It could be extrapolated to several models of receivers and sound bars. No power? Just find if the PSU has the famous 22nF 630V film cap in primary section and 90% you’re done. Never thought that could even be extrapolated to something so different like this.

[budm]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

If I remember correctly, this power supply uses PFC Voltage booster to boost up the DC produce from the main line to be > 380VDC.
@230VAC the voltage on the cap will be around 325VDC without the PFC Voltage booster circuit.

[budm]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Is this the monitor you are working on?
http://s807.photobucket.com/user/bud...tml?sort=3&o=0

http://s807.photobucket.com/user/bud...?sort=3&page=1
A lot of people do the fixing by taping off one pin of the connector:
https://www.youtube.com/watch?v=4dMPtczFwDs

Some people will change the power supply to higher Wattage.

But the actual cause of the problem is due to output of the regulator went too high. so sooner or later the other circuits on the board will be damaged, putting tape on is just fooling the protection circuit.

[Chungalin]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Yes, this is the monitor. I’ve found the video with the center pin masking. It’s the first thing I’ve tried, to no avail. Anyway, the symptoms were different, but was easy to try.

By the way, I’ve analyzed the output connector and the center pin is just connected to a 4k12Ω SMD resistor, and this one to ground. Seems a test pin, but nothing that affects the PSU operation nor a protection. The output connector is just connected to +24V, GND and to the mains earth.

[budm]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

That is sensing pin for the monitor to verify what size of the power supply is connected to is not less than the minimum requirement and it will not allow the monitor to come on (and give error) if the Wattage of the power supply is too low.
I still doubt very much if that cap is directly connected in parallel with the main filter cap.

[retiredcaps]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

The capacitor is almost identical to the one that fails on Yamaha receivers (several models affected), pictures here:

Dave Jones at eevblog ran into this problem too in episode 378 and 379.

http://www.eevblog.com/2012/10/31/ee...-receiver-fix/

http://www.eevblog.com/2012/10/31/ee...ardown-repair/

[budm]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

That cap is the used for capacitive power supply circuit, it is basically used as the Voltage dropping resistor, not connected in parallel with the main filter cap.
https://cdn.badcaps-static.com/pdfs/...5df14516be.pdf
https://cdn.badcaps-static.com/pdfs/...4cc8de4108.pdf
http://michaelgellis.tripod.com/capsup.html

I use this kind of setup in lots of the products I designed.

[Chungalin]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

I've attached pictures of this thing. First, the actual cap. Then, the board, both sides. And finally, two pictures trying to show that this cap is in parallel with the primary filter cap (wrapped in yellow tape). I've put a light behind the board because these tracks are on the component side.

[Porto]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Hello,

To revive an old topic...

I believe I have a similar problem with an 23" Cinema display with exact this powersupply; I want to check inside but can you tell me how to open the case without causing too much damage to the housing?

Is the case glued or clicked in place?

Thank you!

Davy

[Chungalin]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

I open it with hammer and flat screwdriver (much less destructive than you’re thinking, believe me!!)

It’s glued, like many chargers and power supplies. No screws nor claws. I use a flat screwdriver, a 5mm wide blade is enough. Insert the blade in the slit and hit with the hammer until you hear a *crack* sound. It’s not a matter of cutting or piercing, but breaking. You have to measure your force. Start from near the open connectors. Once you have heard a few cracks along the slit you can start to pry open with care. I’ve never left an adapter unopened with this method, and they always can be closed back with cyanoacrylate (superglue3) or hot glue.

Before opening the adapter, please check that the voltatge is 24V whitout charge and that it drops and rises when plugged to the monitor. Otherwise (24V stable), there’s nothing to do inside the power supply.

Good luck with your repair and, if it’s the same capacitor, please report back!!

[Porto]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Thanks Chungalin, I'll try your method!
Some also say it's kinda ultrasonic welded together but your method also works on those cases.

I checked pins 2 and 4 on the connector and there is no voltage at all present so maybe I have a bigger problem than only that cap inside the power supply!

[Porto]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

It’s glued, like many chargers and power supplies. No screws nor claws. I use a flat screwdriver, a 5mm wide blade is enough. Insert the blade in the slit and hit with the hammer until you hear a *crack* sound. It’s not a matter of cutting or piercing, but breaking. You have to measure your force. Start from near the open connectors. Once you have heard a few cracks along the slit you can start to pry open with care. I’ve never left an adapter unopened with this method, and they always can be closed back with cyanoacrylate (superglue3) or hot glue.

Before opening the adapter, please check that the voltatge is 24V whitout charge and that it drops and rises when plugged to the monitor. Otherwise (24V stable), there’s nothing to do inside the power supply.

Good luck with your repair and, if it’s the same capacitor, please report back!!

Well, I managed to get the case HALF open, only the backside (side with the connectors) won't break. I didn't use the screwdriver because the head begins small and goes thicker and thicker so you get quite some damage on the edges of the housing itself. Instead, I used a very small but strong stanleyknife to cut in between that seam. You have to be much more patient but I got it open little by little with the help of a hammer with rubberized head.
Unfortunately, I slipped two times with the knife so now the housing itself has two 'scars'.

I can smell a toast odor coming out the housing so I guess something has released its magic smoke!


UPDATE: ok, got it completely open now. The PCB is encapsulated but that won't be a big problem.





Seems like especially the corners are the hotspots for cracking open this POS.

[Porto]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Got the encapsulation off of it and immediately some SMD resistor fell out of it and there is a burning spot on the inside, so this will be a real project!

And what do you know? That is some nasty shit going on there!





Seems that the complete PCB layer is toast and it's one charcoal mess... to reconstruct this without a schematic is difficult I guess!


A view of the board of the OP:




Need to be two SMD resistors over there, I can try to mount them but what is the cause of them blowing off the board like that in the first place?

Someone know of a schematic of this PCB, I can't find any on the Net.

[TechGeek]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

That stuff is NASTY!!

[squeeish]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

I've the exact same rise and fall of voltage as OP described. Fingers crossed this works, and many thanks for this thread, otherwise I'd have never found the problem.

[squeeish]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Welp that didn't work. I also replaced the 3 220uF capacitors to no avail.

I was thinking of getting a 25V 4A generic power supply and hook up the connector board to it. That should work right?

[TechGeek]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

Is the Apple Cinema adapter center-negative or center-positive?

[Joe Black]

Re: Apple Cinema HD Display LCD 23" (A1082) with 24V power supply (A1097)

You can easily determine that with a DMM.