peterbayrealty wrote:
I haven't read through all the suggestions, but when I have a blown board, I do not try to fix it because of the simple reason that many other IC's are also blown when the "fuse" blew. The fuse acts too slow to prevent the other components from being damaged!
The only jub of this fuse is to prevent fire on the board! I had this happen many times in the last 20 years in the PC business.
The good intentions of others are admirable, but all the help they suggest will just lead to frustration and maybe loss of all data after you think you have the correct component.
The only practical and only real solution is to buy another identical knows working drive (ebay, craigs list, etc.) and swap the board.
Sometimes this didn't fix the problem either, because there is a read/write head pre-amp inside the drive itself which was also blown. This is another tiny circuit board with electronics on it inside the cover. There's no way you can replace this yourself.
If you try another board and it doesn't work, your only solution is to send it to someone that specializes in data recovery. The actually remove the platters in a clean room environment and install it in a known good drive to recover the data.
Trust me, fooling around with replacing components is useless. I've been there and done that many times, and never was able to fix a board. Swapping it with a know good one is the only solution.
It is not the fuse that protects the circuits, its the TVS. And it is blazingly fast.
Look what I found:
http://www.semtech.com/pc/downloadDocument.do?id=509 (pdf)
It says there that TVS are designed to short-circuit at a certain voltage keeping the voltage over the protected element at that limit.
They work extremely fast so you can stay assured, when they worked, the PCB and all the chips on it did not get overvolted and fried.
The fact that it takes a while for the jumper to blow doesnt affect that. All the time the jumper heats up before it blows, the TVS keeps the current flowing through itself, protecting the vital circuits. The jumper's role is to blow before the TVS does.
Pretty neat, eh?
Of course this protects the drive mostly only from external over-voltage, such as a surge, a faulty psu, or mixing up the 12 and 5 volt lines.
Its a different matter if the fault happens inside the 'safe zone' protected by the TVS.
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