Finding a hard drive PCB chip (TVS)

[lasergecko]

I've got a seagate hard drive with a bad PCB, I think the TVS (transient voltage suppressor) was overloaded so now it is a short. When I plug the drive into a computer power supply the whole computer will not turn on. When I plug the drive into an enclosure, the enclosure does not turn on.

On advice from a HD expert, they said to remove the TVS chip and then try it. I'd like if possible to replace the chip. The chip is labeled as ON (in circle) 645 LEM. Anyone know where I can find such a chip? My attempts at finding one via google weren't successful.

Thanks in Advance.

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Moved to gen Hardware
AnandTech Moderator Evadman

 

[rivan]

This might go better in general hardware, but I'll make the assertion that it might be easier to find a whole new hard drive, the same model, and take the whole control board from it.

 

[Arkaign]

Per my experience, it's actually better to buy an IDENTICAL used hdd off of ebay, and transplant the whole PCB, than to try to mess with individual chips. I assume the data on the drive is the valuable thing you're looking for here (worth the price of a used HDD).

 

[lasergecko]

I was able to buy some drives that have the same firmware and model number but it seems like they use different chips. So when I put the new PCB on the drive it doesn't seem to work. (The bios seems to think something is there but the drive doesn't respond in time.)

It was suggested that I remove the chip which seems like it could be a better solution.

 

[PottedMeat]

The circle 'ON' is the manufacturer's logo - On Semiconductor.

http://www.onsemi.com/PowerSol.../parametrics.do?id=824

I'd just remove the TVS, dump the data, get rid of the drive.

 

[compuwiz1]

With storage so cheap now, why fuck with it?

Or maybe you need whatever is stored on it. Try finding a used exact same drive somewhere and pillage from it.

 

[nineball9]

Many transient voltage supressors are just zener diodes. If you have a meter with a resistance range that uses 0.2V or there abouts, you can measure the TVS. (Some meters will have a single resistance range with a diode marked on it. The other ranges use higher voltages to measure resistance.)

If it's a silicon zener, it will most likely short if bad, so if you measure it with a low-voltage resistance range, you will get a low reading. If it's good, you will get infinite reading measuring in both directions with a low-voltage resistance range. With a higher voltage range, (over 0.7V), your meter will bias the diode. Measuring in one direction will be infinite (or high, zeners are funny as you will be reverse biasing the diode which is how it works). In the other direction you should get a reading, 800 - 2,000 ohms; it varies.

In the unlikely chance it's a germanium zener, it will most likely open if it fails. If it's bad, all resistance measurements will read infinite. If it's a good germanium zener, you need to know the voltage used by your meter for resistance measurements as germanium diodes will usually forward conduct at 0.2V, though with experience, you can get an idea of its condition by measuring in both directions.

If the TVS is just a zener, it probably clamps to ground, in which case you could remove it (and lose circuit protection.)

You could also do voltage measurements, but I suspect you are simply guessing the TVS is bad. Real troubleshooting doesn't work very well by guessing unless you've been troubleshooting for years.

Good luck

 

[lenjack]

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