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I put the machine back together as I need some space for other repairs right now. Aimed a bright LED light at the center of the screen and powered on. For a split second I see white lines on the screen, not visible without the LED light pointed at it. This is the same time as the chime is heard...

The meter figures out the range itself, it picks up 5V as well as 60V or 0.020 mV and displays it properly. That said I don't have years of experience using a meter so.. that's just my observations. Would the Mac still chime if there's a CPU issue? A known-good display was tried before it was...

It does chime yeah.

No liquid damage reported or found. L8300 gets a split second pulse where the meter shows 0L but then 0V immediately after on both pins. An external screen receives no signal from either Thunderbolt port.

No continuity in the middle pads. When I removed U7701 there was a lot of corrosion on the center pads and bottom of the chip. I cleaned carefully with alcohol and a q-tip before I did any wicking and it ws already in bad shape with the center pads gone. With the wicking I took the two outer...

Thanks smiba, R8300 Pin 1: 0V Pin 2: 0V J8300 looks good, all pins are connected properly. To check BKLT_EN_R I need to measure pins on U7750 which I currently can't do with the meter probes I have. Should be able to check later this week though. Using the probe point and R7756 to measure...

Unit posts but display stays black. Checked with flashlight but can't see anything. Tested with another screen and same issue. Still new at this so tracking an issue through the schematics is still a little difficult. That said I took the following readings: Q7706 Pin 1: 0.53mv and dropping...

Corrosion on U7701 and surrounding components. Cleaned it up and removed U7701 to find corrosion destroyed some pads. The board itself is very soft under U7701, like working on paper maché. Pins 2,3,4 I can get back with jumper wire but 8,9,13,14 I have no idea how to go about that. Is this...

Alright, Got it :)

That works, thanks!

I'd still like to have some good sources of components in case I don't have or can't find a good donor board.

Any pointers as to a reliable source for parts? Checked mailin.repair and mouser but this chip is not supplied on one and not in stock on the other.

I have a few for 2009-2011 iMacs but nothing newer. Are they out there that anyone knows of? I've been asked if I can repair the boards but of course this all depends on the schematics and boardviews :)

Thanks guys, that helps. So JTAG and backlight fuses I hear a lot of grumbling about is all liquid damage related?

Howdy, Does anyone have a list of known common issues they can point me to or share? I know about the capacitor issue on 820-2610 and 820-2850, the GPU issue on 15-17" 2011's and RAM slot pins on 820-3115. But are there more common issues like this? Reason for making a list like this is to...

Yup, heated the GPU and issue was "resolved". What are the chances of finding a good GPU for this model 6-7 years later, worth having it repaired? (I don't have the equipment needed to replace such large components).

Alright, will give that a try in the morning. Thanks for the help so far!

What's the best temperature to do so and for how long?

When I boot with ALT I see the boot picker, I can select other external drives but when it gets to a point something should show on the screen, all I get is white. In the case of ASD which has a blue background, all I get is blue. Don't want to start blaming the GPU right away but in this case I...

Thanks dukefawks. I did none of those things as I can't replicate the problem to begin with. With that and no visible issues, this is a no-fix. Appreciate your time! :)