What is a oscilloscope for in data recovery?

[zed]

Hi All,

I have heard on this forum that people use a oscilloscope, what do you use it for? I do not own one or never used one. What is it useful for regarding hard disks?

Thanks for your help.
Zed

[BlackST]

How can do without? Unless you rely only on diag by software... I trust only hw.

[rchadwick]

An Oscilloscope plots a voltage over time. This lets you see what a voltage is doing. A Volltmeter will only tell you what the voltage is at the moment, and is often inaccurate with fluctuating voltages. Basically, if you want to measure a battery, or a supply voltage, a DMM is great. If you want to see a fluctuating voltage, like the drive to a spindle motor, or the ripple in a power supply's output, a scope is the way to go. If you don't have a decent electronics background, you likely won't know what you're looking at, or how to set an oscilloscope to produce a waveform.

[craig6928]

checking that the preamp head is getting a signal
and allso doing motor checks.

[rameez]

Also for measuring frequency of oscilators .

[zed]

Thanks all for the reply - where would you place the probes to best use for hard drive pre-amp or motor diagnostics? I have never used one and have read on wikipedia how it can be used for many uses.

e.g In many cases i get a hard disk with a burnt motor controller chip. I order a new PCB and only find the disk is clicking with a new pcb (confirmed compatible pcb) then find out the pre-amp is also damaged once the drive is powered up. So i'm trying to find a way to test the pre-amp before i buy the donor drive so i can give my customer an accurate quote, not 1 price then later increase the price when i find the disk has a damaged pre-amp too.

Thanks to all for replying so far.
Zed.

[shaun]

If you ask where to place the probes, you obviously do not have the knowledge in electronics necessary to interprete what you see on the scope screen. To check whether the motor is driven, you place the probes at the motor connector of course. With the appropriate knowledge you will be able to decide whether the signals you see are the right ones to drive a BLDC motor, and with some more experience you can also say what the motor is doing from the back EMF portion of the curve that can be seen on the phase leg not driven at a specific time.
Same with the head amp, the multiplexed outputs are accessible on test points on some drives. But what will you do when you see the one or the other waveform? No waveform while the disk spins, the preamp is powered and enabled is of course a sign of malfunction.

[zed]

Thanks shaun, my plan was to examine several working drives with a oscilloscope to learn what a working drive looks like compared to that of many faulty disks i have in here which i have been collecting for furthur research.

Thanks for your tips.

[N.C.]

Thanks shaun, my plan was to examine several working drives with a oscilloscope to learn what a working drive looks like compared to that of many faulty disks i have in here which i have been collecting for furthur research.

Thanks for your tips.

Hi,

I am affraid, the case is much much more complicated.
The signals, what you waiting for, sometimes comes only from a division of 1 second!
Sometimes the perfectly skilled persons can't catch them also on first time!

I think, you will have a really hard lesson to use the scope first on hard drives.
You need much more electronic knowledge before run for the measuring hard drives....

Anyway, good luck!

Janos

[BlackST]

...or need a digital storage scope for signal analysis. I have also found other use too: paperweight, door lock... LOL

[N.C.]

Yes, a little bit easyer to use an digital sore oscilloscope.

[zed]

Actually, i was looking to purchase this one - do you think this is a good one to buy considering i may not use it often and it won't take up too much space? + it's portable for using on-site at clients locations if needed.

http://cgi.ebay.com/Uni-T-HANDHELD-Digi ... .m14.l1318

[TerraNova]

Not good enough Zed, you need a digital oscilloscope with high bandwidth like few hundreds Mhz.

[rchadwick]

That one's cute. It's a nice, low cost handheld unit. One might also call it a toy. It's limited by a few things:

1) Likely low resolution screen will limit it's ability to see trace details
2) 8MHz bandwidth is tiny. It will let you see the basics, but forget about looking at the signal from the heads.
3) Not that it matters too much because of the 8MHz bandwidth, but it doesn't even have BNC connectors for real scope probes.
4) It's a single channel. Real scopes have 2 to 4 channels. Sooner or later you'll need to look at 2 things at once, and you'll wish you had a dual trace scope.
5) I've never heard of Uni-T. Most professionals are drawn to name brand equipment, as weird quirks get old fast.


It might be a nice beginner scope, but you probably won't get much out of it. A better first scope would be one with an analog display, and old fashioned knobs to turn. If you don't deeply understand scope usage, a digital unit can be confusing. For DR work, I'd recommend a 60MHz to 100MHz scope with a CRT, and a waveform storage function. If you're looking for a beginner's scope, an analog 20MHz unit would be great. Getting a cheap scope, then the right scope, is a lot cheaper than an expensive mistake, then the right scope.

Also, don't be afraid of used equipment. A well maintained scope can and does last 20 years or more. A 20 year old scope with good specs might be cheaper than the handheld unit, and much better.

[shaun]

Agree, but 100MHz seem a little bit too low for head signals. Even a 400MHz is at its end when it just comes to verify the data from the head amp as data rates reach 600MBit/s per channel with recent PR heads and not much less for traditional GMR. I was quite happy with a two channel 200MS/s HP DSO when hard disks had about 2GB, but now I'm often guessing around with a 100MHz analog scope. I definitely need something bigger (not only for HDD jobs, but mainly for electronics development), for the last projects I used the university's LeCroy and R&S with up to 20GS/s, far beyond the price I'm able to pay of course.