Dead harddrive...

[cs.dk]

One of my friends have a toasted harddrive.

A diode on the input is dead, he tried a pcb from a similar disc, but it did not work. The discs were not exactly same ones by partnumber, the drive was spinning up, but BIOS could not see it.

Why is the diode toasted? - I could swap the diode from the other pcb, which have a similar one, but will the "smoke" get out of it? This is the last chance to save something from the drive. The data is not that important, so Ontrack, and similar company's is not an option.

Thanks

EDIT: Forgot the pics!!

[SeanB]

Reverse current and overvoltage zener diode. Either the power supply is dying and giving high voltage or spikes or the diode died from an internal degradation. Just remove it and try again. Very common to see that failure.

[free_electron]

Overvoltage protection diodes.  Buy new power supply and new drive , then Desolder them , get data off drive on new drive.

[SeanB]

Still have a few drives running with those diodes removed ( not my computer, and anyway the only thing on there is a XP install with a networked docs folder and a install of Office 2003 that will be upgraded to 2010 with the new hardware ( and win7) when this one finally dies) and a new cheapie power supply to replace the 5 year old one that did it in. If the users keep data not backed up it is their problem.......

[cs.dk]

Thanks alot.
Will try to remove or replace the diode to get the data off the drive.

[Falcon69]

I blew the same diode.  I had my harddrive in one of those External cases.  DIdn't realize before it was too late that the plug for my laptop, also fit the same jack for the external harddrive.  I sent 12 volts to the drive, instead of the 5volts. Popped the diode right away.  I simply did alittle research on the net, found the part number for the diode, ordered it, and soldered on the new one. Drive worked again.  Got rid of the external enclosure.  The risk was too high, being that the power plugs for both the external enclosure and the laptop were the same size plug.

[peter.mitchell]

I blew the same diode.  I had my harddrive in one of those External cases.  DIdn't realize before it was too late that the plug for my laptop, also fit the same jack for the external harddrive.  I sent 12 volts to the drive, instead of the 5volts. Popped the diode right away.  I simply did alittle research on the net, found the part number for the diode, ordered it, and soldered on the new one. Drive worked again.  Got rid of the external enclosure.  The risk was too high, being that the power plugs for both the external enclosure and the laptop were the same size plug.

How to solve that problem? Solder the plugpack to the drive - that way you never lose the plugpack either.

[cs.dk]

Reverse current and overvoltage zener diode. Either the power supply is dying and giving high voltage or spikes or the diode died from an internal degradation. Just remove it and try again. Very common to see that failure.

You vere absolutely right - Removed the diode, and the drive spins again. All data is off the disc now. 
I just don't get it - When i remove the diode, the is a "open circiut", how can the drive spin without it?

[c4757p]

The diode doesn't pass the power through it, it shorts out the power if the voltage goes too high or backwards.

[digsys]

Reverse current and overvoltage zener diode.... Just remove it and try again. Very common to see that failure. 

You vere absolutely right - Removed the diode, and the drive spins again. .... I just don't get it - When i remove the diode, the is a "open circiut",
how can the drive spin without it? 

It's a protection device that sits ACROSS the Power rails, ie in parallel. For most it's life it will never be needed. People RARELY use series diodes.
That creates lots of other problems.

[elliott]

The diode doesn't pass the power through it, it shorts out the power if the voltage goes too high or backwards.

This would be referred to as a crowbar circuit, right?

[c4757p]

Well, I suppose, a crowbar diode. Don't call him a circuit... he gets a bit arrogant and smug when he hears that...

[digsys]

  This would be referred to as a crowbar circuit, right? 

Depends. Some devices are act as ZENERS. They simply maintain a max votage (and short cct a reverse voltage). Other devices,
ie TVS (Transorbs) Gas arresters etc will SHORT everything as soon as they reach trigger point. Plus you can have UNI / BI directional types.
Each has a purpose.

[c4757p]

Good point. A Zener diode will just absorb a transient, but many protection devices will happily completely crowbar the power supply if the voltage goes a bit high for a microsecond.

[Psi]

Some devices are act as ZENERS. They simply maintain a max votage (and short cct a reverse voltage). Other devices, ie TVS (Transorbs) will SHORT everything as soon as they reach trigger point.

You sure about that? it doesn't sound correct from what i understand of TVS diodes.

[digsys]

  You sure about that? it doesn't sound correct from what i understand of TVS diodes. 

I may have them mixed up :-)  I was too lazy to x-check. There are sooo many different types of protection devices with different behaviours.
Sure is hard to let things get past in here :-)

[c4757p]

Normal TVS diodes behave like Zeners. There is the "Trisil" (not sure if there's a generic name for it), which behaves like a thyristor.

[Psi]

Yeah, thats what i thought, TVS are just zeners designed to handle high energy pulses.

You could use a TVS to make a voltage regulator, it just wouldn't regulate very well due to having such a wide voltage range between conducting and clamping.

Conversely you could use a zener to absorb voltage spikes but it couldn't handle anywhere near the energy levels of a TVS.