i have a few seagate archive 8tb drives that don't seem to get any power. a board swap will allow them to power on, but of course they will click a few times before turning back off. i think i have checked the e-fuses correctly. is there any other things i can check to resurrect these drives?
Can you check the resistance between V3 and ground on each PCB? This will tell us if the MCU core is shorted. Be aware that the inductor pins may be coated with PCB lacquer, so you may need to scrape them with your probe tip to make sure they are making proper contact.
I expect that the core resistance will be around 100 ohms.
It looks like the motor controller IC is not generating the second Vcore supply. That's either because it is faulty, or because it is not being told to turn it on.
The drive does have a terminal port which outputs diagnostic messages, but you would need to purchase a 1.8V TTL-USB adapter.
There are three other ICs (MOSFETs) which perform voltage switching. If you can locate the 3 motor pins (connector J7), there are two ICs nearby, one 8-pin and one 6-pin. Measure the voltages at each pin. Many pins will be connected together, so you only need to measure one from each group. You should measure +5V or +12V (I don't know which).
There is another 6-pin MOSFET to the left of the 5V e-fuse. Measure its pins also. Be careful not to short pin #3 to its adjacent pin. Likewise for the other two MOSFETs.
There is a small white shock sensor near one of the screw holes. There is an inductor nearby, and above it is a diode. Measure the voltage between the anode of the diode (non-striped end) and ground. If this voltage is being turned on, it will probably be -5V (or maybe -3V).
thank you for all your help. i have to leave soon. i will check those voltages later tonight. in your opinion, is it worth checking the voltages, or would it be more beneficial to buy the ttl-usb adapter?
One other remote possibility is that the drive is configured to Power Up In Standby (PUIS). However,I don't know if any voltage would normally be missing under such circumstances. In any case you should still see something in BIOS.
You can wake up a PUIS-enabled drive using HDAT2, or you could boot into Linux.
The missing Vcore supply is generated within the motor controller IC. The only really wacky thing you could try would be to connect V2 and V3 with a wire. Then you would have a single Vcore voltage powering both cores. But it would only be something I would try if I had nothing to lose.
If you want your data, I would purchase a replacement PCB and transfer the "ROM" chip.
By the way, do all your PCBs have the same "fault"? If they do, then the missing Vcore may be a symptom rather than a root cause.