two diferent WD 2500JS with problems

[MAD1974]

I have two hard disks WD2500JS, one turns and stops.
The other will not start. The PCB This shorted.
Some help please.Sorry for my English, use the google translator

[fzabkar]

Could we see a detailed photo of the shorted PCB?

[MAD1974]

This is the PCB.

Attachments

[fzabkar]

The +3.3V Vio supply is down. If this is due to a short circuit, then U12 must be suspect. I would confirm the resistance between pins 8 and 4. If the resistance is not close to zero, then I would measure the voltages at the 3 pins of transistor Q8 near the preamp contacts. I would also measure the voltages at the anode of diode D4 (-5V) and resistor R050 (~ 1.2V).

If U12 is OK, then you could transfer it to your good (?) PCB.

Here is a similar layout:
http://malthus.zapto.org/download/file. ... &mode=view

[MAD1974]

R between pin 8 and 4 is 0.1 ohm , V in Q8 , 5v 5v 0v , V in D4 0.2v and 5.1v

[fzabkar]

R between pin 8 and 4 is 0.1 ohm , V in Q8 , 5v 5v 0v , V in D4 0.2v and 5.1v

There is definitely a short on the Vio supply. Assuming the negative supply is -5.1V, then that's OK. It is tellling us that the motor controller is probably functional. The fact that the base-emitter voltage at Q8 is 5V means that Q8 has failed, probably due to the short. The motor controller is still driving the base, though, so this is further confirmation that it is probably OK.

Now you need to determine which component is responsible for the short on Vio. It could be any or all of the MCU, SDRAM or the serial flash memory (U12). Carefully desolder pin #8 of U12 and retest for shorts. If U12 is OK, then transfer it to a known good PCB, or try to read it with a chip reader.