DIY Read Channel Shorting Tool

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sebykos

New member
Hi guys,
My "famous" ST3000DM001 failed last week, and since then, I'm reading every forum and watching lots of data recovery videos (many thanks Jared, for your responses on YouTube :) ), and I'm begging to get quite a good picture regarding the recovery process. The subject started to captivate me, and it would make a nice learning experience.

Most likely the drive is stuck in the BUSY state. Spins up, the heads seek a few times, no strange noise, but the computer POST takes a lot of time, then the computer finally boots from an SSD, but the case HDD led remains ON permanently(I guess this is a cheapo way to confirm the issue, without professional tools like pc3k)

Now I was considering to try shorting the read channel. If I succeed this operation, will the drive be accessible from the SATA port as well? or only from the serial terminal connection? I understand that this is not a permanent fix and it will be required to be done every time I power on the drive... but can it work?

Meanwhile, I have removed the PCB, and I'm trying to identify the read channel.
I couldn't find pictures with exactly the same PCB model, but it seems to be very close to the one in the video above, with the shorting foil https://www.youtube.com/watch?v=_Mrvo87WvF8

Can you please confirm that I have identified them correctly here? Or is it the reverse?
I know I should search for the controller datasheet, but I don't want to ruin that thermal pad.




I need to mention that I have successfully cleaned the black residue surrounding the holes using a bit of scotch tape, they are now gold and shiny :))
 

Jared

Administrator
Staff member
I don't have a picture of that exact PCB number, but here's a very similar one with the read channel circled:
100664987.jpg
 

sebykos

New member
Hi Jared, thanks a lot for your kindness, indeed the PCB is very similar, however I found another similar board on HDDguru, and they point to the other pair, also in the video linked by michael chiklis there is a similar model and he shorts the other pair https://www.youtube.com/watch?v=_Mrvo87WvF8
Then to make things even more complicated, there is page 26 in this document from MRT http://en.mrtlab.com/wp-content/uploads ... ircuit.pdf containing an obvious mistake, because they circle the left pins in both pictures, and they should be always in the reversed side when flipping the board.

In conclusion, if I accidentally short the Write channel, is it riskier than the read channel?

Also from my previous post:
"f I succeed this operation, will the drive be accessible from the SATA port as well? or only from the serial terminal connection? "
 

Jared

Administrator
Staff member
The only risk is you might burn out the PCB. I think I had that happen once to me.

My picture might be wrong, I'm not 100% sure. I probably took an educated guess, shorted there, and it happened to work. Maybe it was the wrong one.

It's been a long time since I've actually had to short a read channel. Usually, my other methods almost always work.
 

LarrySabo

Member
This post by fzabkar should help you to identify which is the read channel and which is the write channel.

How to identify the Read Channel when no terminators

Post by fzabkar » Sat Aug 17, 2013 8:53 pm
Some newer PCBs have no visible termination resistors on either the read or write differential pair. In such cases it may be possible to identify the read channel by measuring the two signal pairs both on and off the HDA.

The write channel is driven by the MCU whereas the read channel is driven from the preamp. When the PCB is off the drive, the voltage on the read channel test points will be 0V with respect to ground whereas the write test points will be 1V or thereabouts (possibly 1.8V). When the PCB is on the drive, the read channel test points will now rise to around 1V or so, and the write channel will settle into a similar range.

I'm not certain if the above observation is applicable to all drives, but I have verified it on a Hitachi.
 

sebykos

New member
Thanks guys for the tips.
I have measured today the voltages on those points:
With the PCB mounted, they are around 1.28V-1.32V on all 4 points.
With the PCB removed from the disk the 2 points on the left stay at about 0.25V , the 3rd point is at 0.75V and the 4th one 1.5V.
This would mean that the ones on the left are the Read channel if I understood correctly.

I have attached an image for clarity, notice the shiny contacts cleaned with scotch tape

[glow=red]SPAM Link Removed by Moderator[/glow]
 

sebykos

New member
Hi, that's strange, I used the same image host as in my previous post. I don't even read poems... I guess you were getting some ads/pop-ups

Anyway, I now used the direct link to my picture, with the voltages I measured:
20201005-234141e.jpg
 

Jared

Administrator
Staff member
sebykos":2t10cfeu said:
Hi, that's strange, I used the same image host as in my previous post. I don't even read poems... I guess you were getting some ads/pop-ups

Anyway, I now used the direct link to my picture, with the voltages I measured:

No, it was definitely a link spammed in your post which I manually deleted out. The image I may have accidentally deleted when I was deleting the SPAM link.
 
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