Recovery Force® Data Recovery Forum

lcoughey wrote: ↑Thu Nov 30, 2023 12:30 pm Seems like you are narrowing in on the Smooth MCU that I mentioned previously.

Yes I am. I do want to check out the other areas. But I can see why just swapping the PCB is easier. I don't fancy trying to replace all those tiny components myself. Its a messy rabbit trail.

fzabkar wrote: ↑Wed Nov 29, 2023 7:02 pm If you really are measuring 8.6 ohms and 12.9 ohms at the power connector, then something is seriously wrong right there.

Remove the PCB and retest these two resistances.

Power = Voltage squared / Resistance.

P12 = 12 x 12 / 8.6 = 16.7 watts !!!

P5 = 5 x 5 / 12.9 = 1.9 watts

With the PCB removed off the drive I get this...

P12 = 12 x 12 / 8.6 = 16.7 watts (Same)
P5 = 5 x 5 / 18.7 = 1.3 watts (Changed)

Let Rp be the resistance of the preamp's 5V rail.

18.7 x Rp / (18.7 + Rp) = 12.9
18.7 x Rp = 12.9 x (18.7 + Rp) = 12.9 x 18.7 + 12.9 x Rp
5.8 x Rp = 12.9 x 18.7

Rp = 12.9 x 18.7 / 5.8 = 41.6 ohms

If that's correct, then the preamp is dead.

That said, if the 12V supply is dissipating 16W, something should be on fire.

In short, I don't trust your measurements.

Edit:

Doh!

It would have been far simpler to have subtracted 1.3W from 1.9W, in which case the preamp would be dissipating an improbable 0.6W.

With the PCB removed from drive...

On the molex connector I measured the resistance from 12v rail to ground and got 8.6 ohms, that's correct.
On the molex connector I measured the resistance from 5v rail to ground and got 18.7 ohms, that's correct.

Your equation 12 x 12 / 8.6 is what says 16 watts on the 12v rail.

The only reason why nothings on fire is because the RapidSpar cut the power before anything could go on fire.

Is the preamp inside the drive, would explain why things change when PCB is taken off drive?

So let me know if I'm measuring in the right place or the wrong place?

The preamp is on the headstack inside the drive.

https://hddscan.com/doc/HDD_from_inside.html

Would you mind indulging me by measuring some known resistor values using the same measuring technique?

What do you measure at R519 (near the coil)? I think the marking is "2000".

What about R222 / R223 / R224 (near U200). What is the marking?

What about the 1R00 resistors near Q501?

If the preamp is dead too. Then it's not looking good for this drive.

fzabkar wrote: ↑Thu Nov 30, 2023 8:16 pm Would you mind indulging me by measuring some known resistor values using the same measuring technique?

What do you measure at R519 (near the coil)? I think the marking is "2000".

What about R222 / R223 / R224 (near U200). What is the marking?

What about the 1R00 resistors near Q501?

OK, Standby.

The other PCB photos have a CR201 diode near the power Molex, whereas your PCB doesn't appear to have one. Is there anything under your "Ground" label? That's normally where a 12V would be located. However, that wouldn't account for the low resistance on the 5V side.