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 Post subject: PCB Read Channel
PostPosted: March 22nd, 2014, 15:02 
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Joined: June 11th, 2013, 17:01
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I am trying to find the read channel for the attached PCB. I presume the read and write channels are the ones I have marked. But both give a readout of 0V either when connected to the HDA or not. I have just tried a matching board with the same results, so I presume I have the wrong ones.


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 Post subject: Re: PCB Read Channel
PostPosted: March 22nd, 2014, 15:15 
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Joined: September 8th, 2009, 18:21
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ISTM that you have correctly identified the R/W differential pairs. Are you measuring 0V between each signal and ground, or 0V between each of the pairs?

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 Post subject: Re: PCB Read Channel
PostPosted: March 22nd, 2014, 15:21 
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fzabkar wrote:
ISTM that you have correctly identified the R/W differential pairs. Are you measuring 0V between each signal and ground, or 0V between each of the pairs?

Each the pairs......... How do I test against ground?

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 Post subject: Re: PCB Read Channel
PostPosted: March 22nd, 2014, 15:28 
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ddrecovery wrote:
fzabkar wrote:
ISTM that you have correctly identified the R/W differential pairs. Are you measuring 0V between each signal and ground, or 0V between each of the pairs?

Each the pairs......... How do I test against ground?

Just to clarify, I am testing the channels with a multi-meter. ie one probe on one side of the read channel pair, one probe on the other side of the read channel pair.

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 Post subject: Re: PCB Read Channel
PostPosted: March 22nd, 2014, 15:33 
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ddrecovery wrote:
ddrecovery wrote:
fzabkar wrote:
ISTM that you have correctly identified the R/W differential pairs. Are you measuring 0V between each signal and ground, or 0V between each of the pairs?

Each the pairs......... How do I test against ground?

Just to clarify, I am testing the channels with a multi-meter. ie one probe on one side of the read channel pair, one probe on the other side of the read channel pair.

The DC voltage between each side of the pair will always be zero. You need to measure the voltage between each side of the pair and ground.

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 Post subject: Re: PCB Read Channel
PostPosted: March 22nd, 2014, 15:39 
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Joined: June 11th, 2013, 17:01
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Location: USA
fzabkar wrote:
ddrecovery wrote:
ddrecovery wrote:
fzabkar wrote:
ISTM that you have correctly identified the R/W differential pairs. Are you measuring 0V between each signal and ground, or 0V between each of the pairs?

Each the pairs......... How do I test against ground?

Just to clarify, I am testing the channels with a multi-meter. ie one probe on one side of the read channel pair, one probe on the other side of the read channel pair.

The DC voltage between each side of the pair will always be zero. You need to measure the voltage between each side of the pair and ground.

Sorry to be dumb, but how do I do that. Put one probe on one side of the pair and touch the computer chassis?

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 Post subject: Re: PCB Read Channel
PostPosted: March 22nd, 2014, 15:43 
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ddrecovery wrote:
Sorry to be dumb, but how do I do that. Put one probe on one side of the pair and touch the computer chassis?

That's one way, but you could use SATA power ground or a screw hole as your ground reference.

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 Post subject: Re: PCB Read Channel
PostPosted: March 22nd, 2014, 15:45 
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Joined: June 11th, 2013, 17:01
Posts: 839
Location: USA
fzabkar wrote:
ddrecovery wrote:
Sorry to be dumb, but how do I do that. Put one probe on one side of the pair and touch the computer chassis?

That's one way, but you could use SATA power ground or a screw hole as your ground reference.

Worked a treat, thanks Fzabkar. Learning a lot :)

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