Chosen Solution
I removed the capacitor on the 5v7 (i think that is what it’s called) line for the display, and it came right back on! But I have a question, do I need to put a new capacitor on there? Or will the phone be ok?
The caps you removed are C4200 & C4201 on the PP5V7_LCM_AVDDH rail.
Capacitors fundamentally do one thing, that is store a charge. They have some amazing properties, which means you can use them for different purposes. In the context of an iDevice, they are mainly used for noise filtering and decoupling (bypassing). You’ll notice that sometimes there is more than one capacitor, mostly different values, in parallel (like C4203 & C4204 above). That is to optimize the frequency response of the decoupling. You also see multiple capacitors in parallel with the same value. That is done to get a much larger capacitance without having to use a big-ass cap when vertical real estate is at a premium, like on an iPhone. Technically speaking, you don’t need to replace them but consider that they were put there for a reason by the Apple engineers.
Capacitors in parallel multiply the current delivery capacity while the voltage remains the same. In short, the capacitor removed should be replaced. The reason is not replacing this capacitor will put additional stress on the other capacitors and the display may have visual effects due to power fluctuations. As an electrical engineer, I frequently put surface mount capacitors in parallel to save space and to provide smooth current flow. These capacitors are rated at 6.3 volts which is very close to the rated power rail and may be related to the failure of this capacitor. I would replace this capacitor and potentially the others with a 2.2uF 10volt version that has the same physical size (0603 metric). Here is a link to Digikey to the component replacement I recommend: https://www.digikey.com/product-detail/e…
