Little help on WD PCB diagnosis, please

[deftrue]

Hello community,

Please I need some help on giving a diagnostic to this PCB, coming from a WD TrailXLS drive. There's defenitely something wrong with it, since the spindle's behavior is quite erratic (random moves, strange noises, sometimes spinning slowly forward and backwards) and using a different PCB from a different drive the spindle goes fine AFAICS. I don't have another PCB like this one right now to compare.

The only (maybe) strange thing I've seen so far is that R15 and its companion measure 735 ohm, whilst R16 is measuring 705 ohm more or less (the three of them marked as 222, which is not very consistent in SMD notation with the values measured as for my understanding, although I guess I should put them apart for a good measure).

Any ideas on what could be going on and how to test it deeply?

Thank you in advance.

Attachments

Western Digital TrailXLS PCB 2

Western Digital TrailXLS PCB

[lcoughey]

Save your time tracing the PCB and order in another and just swap the U12. I'd order an entire drive, just in case I need it for a hot swap or heads.

[fzabkar]

"222" is 2200 ohms. The last "2" is the multiplier.

FWIW, your measurement of 735 ohms is what you would expect if all three resistors were connected in parallel (2200 / 3 = 733). I can see that at least two of the resistors are connected together, so perhaps they all share a common connection. The other end of each resistor is connected to each of the motor's three phases. What resistances do you measure between the motor terminals?

BTW, you might find the datasheet for the L7250 SMOOTH IC useful.

[deftrue]

Thanks, both of you!

A new PCB is on the way since I couldn't get to the actual problem...