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I'm trying to trouble shoot PCB issue on this Maxtor DiamondMax Plus 9 120GB... Drive is not spinning up at all, no power. I think there is a short on the PCB. I've taken readings with multi-meter in diode mode as shown below, measurements are in uF...

That was an era of drive where the Smooth MCU chip would frequently fry. I tend to swap the board, if I can, just to avoid the rabbit trail.

I'm got a bunch of cases to keep my busy right now, but will see if I can find a working board on our shelf to compare readings.

CrazyTeeka wrote: ↑Tue Nov 28, 2023 4:53 pmI've taken readings with multi-meter in diode mode as shown below, measurements are in uF...

This doesn't make sense. uF is a unit of capacitance.

I would identify the power supplies and measure the resistance between output and ground, or measure the voltages.

Q501 (near 4-pin Molex connector) appears to be the pass transistor in a linear regulator.

VR400 (near SATA power) is an LDO regulator.

VR300 (between SDRAM and MCU) appears to be another pass transistor in a linear regulator.

The anode of the diode in Q500 would be the -5V (?) supply for the preamp.

Datasheet for BA18BC0 (VR400, 1.8V LDO):
https://www.farnell.com/datasheets/2100306.pdf

Datasheet for 2SD1758 (Q501, NPN transistor):
https://www.mouser.com/datasheet/2/348/ ... 201467.pdf

... or FJD3076 (Q501, NPN transistor):
https://www.mouser.com/datasheet/2/308/ ... 123972.pdf

Datasheet for FSS139 (VR300, P-channel MOSFET):
https://digchip.com/datasheets/download ... ber=FSS139

Datasheet for FW503 (Q500, MOSFET + diode):
http://datasheet.digchip.com/413/413-3502-FW503.pdf

Your PCB may have different ICs, but they would be functionally equivalent.

Other photos:

https://cdn10.bigcommerce.com/s-9c16le9 ... 80.JPG?c=2
https://datarecoverydonors.com/cdn/shop ... 1619636581
https://ae01.alicdn.com/kf/S6e61a994c9f ... pal-IC.jpg

I know I can figure this out, with a little hand holding. I checked the resistances (Ohms) from different points to ground. Does this help identify where the problem is?

Well as far as I can tell there appears to be a problem around the Q500 area.

If you really are measuring 8.6 ohms and 12.9 ohms at the power connector, then something is seriously wrong right there.

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.

The readings are correct so something is defiantly wrong with this PCB. What should the readings look like on a working PCB?

I could measure the resistances across each component instead of over the circuit. If that helps?

The L7250 motor controller is powered from both 12V and 5V supplies.

https://pdf.dzsc.com/L72/L7250.pdf

If this chip is responsible for your low readings, then it would be cooking.

Found problem area, many things appear to have blown...

Seems like you are narrowing in on the Smooth MCU that I mentioned previously.