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 Post subject: Inside knowledge of preamp design, etc
PostPosted: January 4th, 2021, 15:59 
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See the posts by "free_electron" in the following thread:

https://www.eevblog.com/forum/beginners/what-to-do-with-a-hdd-motor/msg129452/#msg129452

He makes some contentious statements about head crashes, but his posts are very informative.

This part is particularly interesting:

Quote:
The heads are so sensitive to static discharge that they contain a built in fuse to short the terminals. Once the heads are mounted on the arms , and the arms have been mated with the control chip a special command is sent to the read/write chip to blow the fuses. A verification process makes sure all electrical connections are ok and then the fuses are blown.

Replacement optical pickup units in CD/DVD players are shipped with a solder blob to protect the laser from ESD. Obviously this has to be desoldered. I had no idea that headstacks had similar protection.

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 4th, 2021, 18:28 
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Wow, interesting reading!

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 5th, 2021, 13:17 
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Nice one

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 6:46 
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the 80GB of tables is BS as well, but yeah, informative. For those not knowing it already...
A lot of stuff can be read on doomer's page somewhere, with more precise terminology.
pepe

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 14:14 
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The author claims that the Bernoulli Effect is responsible for the air bearing, but someone pointed out that this would cause the head to be pushed toward the platter. Instead the reason that the head flies is due to aerodynamic lift.

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 16:11 
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From the above he must be talking about “Trimming” (blowing fuses) is used to compensate for process variations- Trimming uses fuse circuitry to address the variations.

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 16:25 
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guru wrote:
From the above he must be talking about “Trimming” (blowing fuses) is used to compensate for process variations- Trimming uses fuse circuitry to address the variations.

free_electron wrote:
i make the chips that sit on the drives :)

I did the preamps ( the read/write amplifier that sits on the arm with the heads ) for about 2 years.

I would hope that he knows what he is talking about. If he meant trimming, then I would think that he would have said so.

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 17:03 
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He makes the chips :)) Not trimming then

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 17:44 
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Those posts were from 2012. I would image things have changed quite considerable since then.

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 18:31 
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Seen reference here https://patentimages.storage.googleapis ... 119995.pdf

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 Post subject: Re: Inside knowledge of preamp design, etc
PostPosted: January 6th, 2021, 18:48 
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This is "trimming" by another name:

Quote:
In another embodiment, the transducing head includes a shunt electrically connected with the sensor element in parallel. The shunt includes a plurality of removable resistive elements, each resistive element having an element resistance, and an adjustable transducing head resistance defined by the sensor resistance and the element resistances. Sequential removal of some or all of the resistive elements establishes a desired transducing head resistance.

It could be said that the head resistance is being trimmed.

The patent also refers to "laser trimming", but in a different context.

So that one patent deals with two processes -- ESD protection and head resistance trimming.

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