Why some HD:s wont work when the case is opened

[Zenator]

So, i've been playing around with some hard drives and i stumbled upon this mystery i want to solve:

I opened my friends external seagate hd (3,5") because the actuator arm was stuck. I could plug in the hd with case opened (so i can see the platters) and it was working fine.

The next day i took ordinary 5,25"(Seagate Barracuda) totally working hdd, opened and tried to run it but it won't read the data, just makes weird noise. But when i close the case again, it runs normally and i can access the data again. I've seen this happen before with other hdd:s as well.

Can someone explain why some of the drive's wont work when the case is open?

 

[WyomingKnott]

Please forgive me if you are serious, but my first reaction to this post is that you are trying to start a big fight.

The answer is that any HDD that has been opened under less than ideal clean-room conditions has a miniscule chance of running ever again. Tiny airborne particulates can crash heads and destroy the media, the slightest force on actuator arms or spinning platters will misalign things permanently. The surprising thing is that the first drive works, not that the second doesn't.

 

[Zenator]

Please forgive me if you are serious, but my first reaction to this post is that you are trying to start a big fight.

The answer is that any HDD that has been opened under less than ideal clean-room conditions has a miniscule chance of running ever again. Tiny airborne particulates can crash heads and destroy the media, the slightest force on actuator arms or spinning platters will misalign things permanently. The surprising thing is that the first drive works, not that the second doesn't.

Thank you for your reply and no, im not here to start a fight.

I do know that it's not a good idea to open the casing in normal room condition, however the thing im trying to find out why doesn't the hdd try to read the data when the case was open, but the data was fully accessable after the casing was closed again? If it was the "dirt" flying around and crashed the head, i wouldn't acces the data nomore afterwards right?

 

[WyomingKnott]

I still think it's freak good luck that the first one works at all. So I don't have anything to contribute on why one might work and one might not.