820-01779 No Video

My reference only: TT9851

iMac came in with no power. We live in Florida so the customer thinks lightning.
At first I thought the power supply was the issue, so I replaced this, I could hear the capacitors making a constant but quiet whining noise.
New power supply came in, this did not fix the issue.
Next, I found a short on C7845, so I replaced this and the short was gone. While looking for the short, I noticed when I put alcohol in the area, the top right of chip U7800 got extremley hot and would turn the alcohol to steam very quickly.
Since I replaced the capacitor C7845, I do get the computer to power on, S0 is also present, I however get no video at all.
The diagnostic LEDS show 1, 2, are on, 3 is out, 4 is just barley lit, and 5 is off. See images.

U7800 is still overheating now?
Check if delivers correct voltage on all its coils.

Is the machine recognized in DFU mode?

2informaticos said:

U7800 is still overheating now?

Click to expand...

Nope, U1200 is getting hot and so is the processor.
I was able to get it in to DFU mode but no matter if I do a revive, restore, update, erase, it never works. I get to step 4/4 and it gets about 35% of the way there, then you hear the fan spin super fast (seems like it may be restarting?), then I get the exact error every single time shown in the photo below.
SSD dead?
Did not check out the voltages on the coils for U7800 yet. Gotta take it out of the iMac.
Oh, I also removed the CMOS battery on the back of the board because it was 2.8v. I wouldn't think this would make a difference would it? I got another battery coming in tomorrow.

It is not turning on now. I see the 1 LED on the motherboard but yesterday I was able to get it in to DFU mode with ease. Since I did all the revives/restores, I cannot get it to power on anymore.

Here are the measurments for U7800, the coils.

L7823: Pin 1 is correct but pin 2 is unstable at .3 then drops to .2.

L7824: Does the exact same thing as L7823.

L7810: .8 both sides.

L7812: .836 both sides.

L7811: Pin 1: .843, Pin 2: .836.

L7809: .751 both sides.

L7808: .751 both sides.

L7807: .751 both sides.

L7806: Pin 1: .767, Pin 2: .751.
I still am getting the computer to go in to DFU mode. When trying a revive now I get the below image in configuarator.

The SSD voltages appear?
Check diode mode to ground on its rails and also all biug coils.

DFU restore gives same error?

2informaticos said:

The SSD voltages appear?

Click to expand...

The voltages were present before I tried doing the revive/restore. I only get the 1 LED light presently (right before this I had no LED lights). This revive/restore is messing with the bootup sequence. I did also retry the restore, but it got stuck. I had it hooked up for over an hour, it just stayed on the 4/4 steps. The revive also took a while, but took about 30 minutes before giving me that above error about DFU to DFU.
Would flashing the ROM chip help?
PP2V5_NAND_SSD0: .392
PPVCCQ_ANI_SSD0: .359
PP0V9_SSD0: .362
PP1V8_VCCQIO_SSD0: .360
PP1V8_SSD0_S4E1_PCI_AVDD_H: .361
PP1V8_SSD0_S4E1_AVDD18_PLL: .361
PP0V9_SSD0_S4E1_VDD_PLL: .366

Erase SoC ROM and try DFU again.
Don't forget to make backup first...

Guess what!? I just tried DFU restore with the screen plugged in and it took the restore! I had the screen plugged in though too previously and it never worked out. Anyhow, I got it doing an internet recovery now. Thank you again so very much!

I saw T2 machines which complete DFU after several tries.
Sometime need to waste days with them...