Apple 15" Studio Display, fixable?

[didius]

I have a 15" Apple studio display hooked up to my cube. Some months ago I noticed the bottom half of the screen being dim and a the led error blink sequence "short - short - short".

According to Apple it means "video output wrong" but the display shows the same error code when hooked up the a powermac G4 MDD, unlikey error it seems.

I decided to open the display and check it's internal organs. Nothing seems wrong, but I noticed the following.

I took both light bulbs out and connected them to the inverter. The top bulb is working, and when I switched the bulbs, the bottom bulb (connected at the top connector) was working as well. Apparently the bottom connection doesn't get any power.

What do you think? Bad inverter board? Or could the problem lie with the logic board? According to someone on Macrumors it could be a heat issue (he had a similar problem where the problem dissapeared when the screen was hot enough - I haven't noticed this yet, the problem is continous)

 

[Macdrone]

I have had to resolder some parts back on the larger displays inverter boards so unscrew it and flip it over.  Usually youll see a small burn on one or the other end of one component there.

 

[oneboyarmy]

We used to have this happen in a previous job of mine. A few of my users referred to it as the "turn signal." Anything I looked it during that time pointed to bad inverter boards, seems to be a fairly common failure with those displays. 

 

[techknight]

Yup. failed inverter board. ive had to change a number of these. Sometimes its just the coupling cap between the transformer and the drive transistors can open, killing the drive signal to the transformer. sometimes its the transformer itself and if its shorted, pops a picofuse, or triggers the overcurrent shutdown inside the PWM control IC instantly upon power on-enable, if its a latched-shutdown itll never re-fire until it re-cycles power. and itll trip again.  

I have very rarely seen burned contacts on the transformers, but I have seen them. Sometimes they are fixable, sometimes not. But realize this: burned PCB material is now carbonized, and also very conductive and will keep burning or affect other adjacent circuits! you must dremel all of that out and remake the connections by hand in worse case scenarios. 

 

[didius]

I've measured a thing or two today.

I started by desoldering the cap on the inverter, it doesn't seem broken since it measured 47 muF as it should. I resolder the joints on the film capacitors. Problem remained.

Then I started measuring the voltages as provided in the service manual.

ADC is giving +25V to the main board instead of the +28V as noted in the manual. I guess it differs between graphic cards (?)

the U5 IC on the main board gave +11.9V (should be +12V) OK

connections 1 and 2 on the J3 connector (main board side) both measured +12V (as it should)

I guess the main board is fine, and the problem must be something on the inverter board, but nothings smells or looks burned.  It is a fact than when I connect the display no LED is flashing. After booting the power led start to blink short-short-short and when I turn the mac of the LED continues blinking short-short-short. This sounds like what @techknight describe regarding the PWM control IC.

@techknight: Any ideas on how to fix this? Getting a replacement inverter board doesn't seem easy...

 

[techknight]

If you can figure out the pinout of the existing inverter, you can use any generic dual inverter to replace it. 

the LED is flashing an error code. There is an error signal that gets raised at the inverter when the inverter itself detects a problem. Whether or not the CPU chooses to ignore that signal depends on the engineer and programmer at the time. 

In this case, the signal is looked at. if it senses an inverter fail, youll get an error code. If you unplug the inverter cable itself going to the main board, the LED should come on and remain on with no blinks. 

the Inverter itself should have a part number or a PCB number, googling this, or eBaying this could lend you some results. 

 

[didius]

I've measured some of the pinout, I know where the grounds are, found two +12V, a +5V, a +3.3V. Sound kinda tricky though.

I guess I'll look for another 15" Studio Display, might try this generic dual inverter as a project. (long term project though)

Thanks for the info techknight!