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reverse polarity diode

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dnolan747

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Hello members,, i am new here and i need a little help with an external hard drive that was brought in to me... the hard drive was being run on a 12v universal plug and my customer reversed the polarity and the reverse polarity diode took the hit,,, my problem is i cannot find anything on this circuit board so i can change the diode, does anyone have or know anything about this circuit board????? Board number is Western Digital Galaxy 1U CR SATA 4061-705002 and diode location is L20,,,


any sugestions would be greatly appreciated
thanks
Dean Nolan
 
Hello members,, i am new here and i need a little help with an external hard drive that was brought in to me... the hard drive was being run on a 12v universal plug and my customer reversed the polarity and the reverse polarity diode took the hit,,, my problem is i cannot find anything on this circuit board so i can change the diode, does anyone have or know anything about this circuit board????? Board number is Western Digital Galaxy 1U CR SATA 4061-705002 and diode location is L20,,,


any sugestions would be greatly appreciated
thanks
Dean Nolan
If the device is under warranty, I believe WD would replace it.
if you know that there is one reverse polarity diode, you should be able to locate one. I fear, the circuits' components would have fried.
 
the hard drive is not under waranty anymore.... and the only component i see that is bad is that diode but i do not have the schematics to know what size diode to use. ... oh by the way it is a surface mount diode
 
the hard drive is not under waranty anymore.... and the only component i see that is bad is that diode but i do not have the schematics to know what size diode to use. ... oh by the way it is a surface mount diode

I don't know what size diodes come in SMD but I'm sure if you can find one rated at 3 amps and 50v or more it should work fine. Most drives don't draw more then a amp or so but maybe a little extra at spin-up.


Lefty
 
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the hard drive is not under waranty anymore.... and the only component i see that is bad is that diode but i do not have the schematics to know what size diode to use. ... oh by the way it is a surface mount diode
you can at least indicate the diode part code found on the component and even perhaps upload a well focused close shot photo of the location so that some one may come up helping you. BTW, if the diode is in shunt path, you my well remove it and then test the drive. if it is in series and now open, you may by pass and test the drive. While doing so, you should not connect a reverse supply !!!

PS: L20 cant be a diode?
please check it might be an inductor.
 
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I had this same problem with one of my external HDDs, I had several 12v PSUs all terminating in 2.1mm power plugs and typically one was reversed polarity. The solution was to put a germanium diode in series with the supply on each HDD so they don't power up with the wrong connector. Or colour code cables if you have very similar ones. The shunt diode blowing voided the warranty of my Freecom HDD as 'it was my fault for using the wrong PSU'.
I don't think having the shunt diode is a good idea as if you are mistake prone (like me) you will be forever replacing it (and eventually destroy the device due to current spikes)
 
I had this same problem with one of my external HDDs, I had several 12v PSUs all terminating in 2.1mm power plugs and typically one was reversed polarity. The solution was to put a germanium diode in series with the supply on each HDD so they don't power up with the wrong connector. Or colour code cables if you have very similar ones. The shunt diode blowing voided the warranty of my Freecom HDD as 'it was my fault for using the wrong PSU'.
I don't think having the shunt diode is a good idea as if you are mistake prone (like me) you will be forever replacing it (and eventually destroy the device due to current spikes)
Worse than that - if the shunt diode blows, and the power supply does not, it applies reverse voltage to the rest of the circuitry. What's the point of a shunt diode that does not blow the fuse (trip the breaker) on the power supply?

EDIT:If it was a series diode, it should not have been damaged by reverse polarity.
 
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Worse than that - if the shunt diode blows, and the power supply does not, it applies reverse voltage to the rest of the circuitry. What's the point of a shunt diode that does not blow the fuse (trip the breaker) on the power supply?

EDIT:If it was a series diode, it should not have been damaged by reverse polarity.

Then comes the issue of Voltage drop across it. we have to have a fuse in series before the diode of suitable rating for the shunt diode to be effective.
 
That's my point. After a couple of times of the shunt diode being forward biased across the supply and the PSU hiccupping until you disconnect the HDD, I changed the way the protection works. The way to do it, I believe is to use a resettable or auto-recovery circuit that 'knows' when you have reversed the input.
 
ooooooppppppsssss my bad

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Quote:
Originally Posted by dnolan747
the hard drive is not under waranty anymore.... and the only component i see that is bad is that diode but i do not have the schematics to know what size diode to use. ... oh by the way it is a surface mount diode

you can at least indicate the diode part code found on the component and even perhaps upload a well focused close shot photo of the location so that some one may come up helping you. BTW, if the diode is in shunt path, you my well remove it and then test the drive. if it is in series and now open, you may by pass and test the drive. While doing so, you should not connect a reverse supply !!!

PS: L20 cant be a diode?
please check it might be an inductor.
__________________
Regards,
Sarma.

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Sarma,,,,, I think you are right I dont know what i was thinking L20 would be an inductor,,,, DUH,,,, i just assumed (and you know where assumptions can get you lol) that it was a reverse polarity diode because of the location right behind the AC plug and it being have been plugged in backwards,,, but this component was fried to a crisp and was broken in half so i could not see any markings on the component.... now that i have been put back on track i will see what can be done...

thanks Dean
 
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If the device is under warranty, I believe WD would replace it.
I doubt it, abuse such as reverse polarity normally voids any warranty - they'd say "hard luck it's not our fault the customer connected it up backwards."
 
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