Mysterious component found on most HDD PCBs - Page 1
Forum section: electronics / beginners

author: tchicago
author_rank: Regular Contributor
timestamp: December 26, 2019, 05:17:15 am
content: Hi, All,I'm curious what is that rectangular glassy whitish component that most of the HDD PCBs have? Attached is a compilation of the various HDD PCBs with that component shown.Some facts about it:- It is positionally marked like MT1 or SK1- It is definitely polar, sometimes the PCB has "+" next to positive terminal- Sometimes there are several of them on one PCB- It is usually installed at a strange angle to the PCB, if there are several of them then they can be at an angle to each other- Sometimes each of them has a dedicated IC next to it. Especially noticeable if there are several of them on different corners of the PCB- Sometimes this component has a guard trace around it, like protecting a high impedance component from the noise.Is it a vibration or acceleration sensor? Or a shock sensor that voids the warranty?

author: LateLesley
author_rank: Frequent Contributor
timestamp: December 26, 2019, 06:11:56 am
content: I did a bit of googling, and it does seem that they may be some type of piezoelectric shock sensor. Here's an example datasheet.http://www1.futureelectronics.com/doc/MURATA/PKGS-00LD-R.pdf

author: Jwillis
author_rank: Super Contributor
timestamp: December 26, 2019, 06:59:25 am
content: They're to detect sudden changes in acceleration ,rotation or impact. The signal from the sensor tells the hard drive to park the head in an instant to prevent the heads from crashing (Head Crash)onto the platter preventing permanent damage to the head and /or magnetic media on the platter surface.

author: tchicago
author_rank: Regular Contributor
timestamp: December 27, 2019, 12:43:24 am
content: Thanks! Really interesting. I guess my next step would be to take some unneeded HDD apart and see how this feature works and how effective it is. Maybe Dave would have made an interesting educational video out of this

author: JustMeHere
author_rank: Frequent Contributor
timestamp: December 27, 2019, 01:40:57 am
content: Free fall sensors have been there for years and have been used to protect the HDD manufacturers from bogus drop claims.

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 27, 2019, 02:20:00 am
content: It would be interesting to take the lid off a HDD and film it being dropped to see what happens.

author: TheGeologist
author_rank: Contributor
timestamp: December 27, 2019, 02:39:38 am
content: Has anyone pulled one of these off to play with? Are they useful for other things such as collision detection?Have many old motherboards and always interested to make use of them before I run out of space and have to dispose of them.

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: December 27, 2019, 04:46:09 am
content: Quote from: tchicago on December 27, 2019, 12:43:24 amYou can also test it on a working drive by performing a data transfer and monitoring it as you simulate freefall. I recall from playing around with this about 10 years ago that from the OS's perspective, the disk appears to freeze, but does come back after a few seconds. Tape a microphone to the drive and you should be able to clearly hear it park and unpark.You can of course film a disk performing this feature, and that would make for good YouTube fodder, but be sure to set everything up 100% before opening the disk because it will start malfunctioning almost immediately due to dust.

author: tchicago
author_rank: Regular Contributor
timestamp: December 27, 2019, 06:13:49 pm
content: Quote from: I wanted a rude username on December 27, 2019, 04:46:09 amI've operated the old HDDs with cover removed countless number of times, writing and reading data, random seeks, etc. They operate for amount of time sufficient for getting bored of watching it work, i.e. at least half an hour. Did it mostly for fun, but also studied the effect of a strong magnetic field using a strong magnet from other hard drive. I does not appear to be affecting the performance of HDD unless the magnet physically touches the surface of the rotating platter. That is probably because the magnetic head operates on a strong and very local magnetic field changing with the high frequency, so adding a significant external "DC" component to that field does not affect head's operation at all.I don't have any good video filming setup, lighting, mic and stuff though, so it could be an interesting to watch if Dave can set it up. With a bonus of poking around with oscilloscope and seeing the output from those piezo sensors.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 27, 2019, 10:36:01 pm
content: Very interesting... glad I'm a magpie and don't throw things away, these could be useful toysAnd their days are numbered, one impact they can't withstand is the growing ubiquity of SSDs, so salvage them while you can!