Question Seagate ST8000AS0002 not turning on ?

Jul 30, 2021
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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?
 
V2 and V3 appear to be the two Vcore voltages.

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).
 
Jul 30, 2021
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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.
 
Jul 30, 2021
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using this photo


Va = 0v
Vb = 4.95v
Vc = 4.95v
Vd = 4.95v


the 8pin mosfet has 11.77v on all pins on the left.... 4.95v on the right

the 6pin mosfet has 4.95v on all the pins on top.... 4.95v on the first two pins on the bottom. the last pin has 11.78v
 
Jul 30, 2021
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the 6pin mosfet near the 5volt efuse has 4.96v on the first two pins on the left. the third pin on the left has 12.25v....... 4.97v on all pins the right side
 
Jul 30, 2021
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oh. well thanks for your help. is there any wacky things i can try doing - like unsoldering a component or adding a wire to bypass a diode - to see if the drive will work?
 
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.
 

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