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

[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)

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]

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?