Shorted hard drive diode - Page 1
Forum section: electronics / projects

author: viktor18
author_rank: Regular Contributor
timestamp: June 11, 2017, 07:51:10 pm
content: So my uncle gave me a external hard drive with around 1000ish photos on which he hopes that I can repair.. (Yeah, yeah, I could switch the PCB which would maybe be easier and make more sence, but what's the fun in that?)It seems like this hard drive has been damaged from the AC adapter, which had burned resistors, probably due to a lightning strike.. So, I decided to test another adapter and the darn thing still don't know, in fact when I plugged it into my external hard drive cable on my PC, my PC immediately shutoff and went into a sort of protection mode.So it seems like the hard drive is shorted.So, I took of the PCB and measure around the PCB, and not so surprised, I found a shorted diode directly across one of the input pins. Photo belowThe shorted diode is ON 825. Don't worry about the weird solder, that's just me doing some mess.Anyway, I tried to find what type of diode this is and could find two possible options. So I'm looking for help for someone experienced with electronics or maybe someone who has repaired hard drive before who can tell what type of diode that would be.My options are:http://pdf1.alldatasheet.com/datasheet-pdf/view/156284/LITEON/SMB18A.htmlorhttp://www.onsemi.com/pub/Collateral/1SMA5913BT3-D.PDF

author: theatrus
author_rank: Frequent Contributor
timestamp: June 11, 2017, 09:24:16 pm
content: The part marking should be ON Semi, so I think its an older (non-B suffix) 10v Zener diode. I'd trace out where its connected to - is it just to protect the power input? Or is it a terrible 12->2V power regulator?

author: viktor18
author_rank: Regular Contributor
timestamp: June 12, 2017, 08:46:59 am
content: I managed to find out that it's a TVS diode, and I found a replacement for it. However, there seems to be two other defect diodes as well, having struggle to find the part for both.Pictures below:S3 86A is the problematic diodeSK 34 is the problematic diode

author: bktemp
author_rank: Super Contributor
timestamp: June 12, 2017, 09:00:30 am
content: S3 -> SS13http://www.vishay.com/docs/88746/ss12.pdfBut when the diode on a buck converter fails due to overvoltage, most likely there is also much more damage to other parts connected to the output voltage.

author: viktor18
author_rank: Regular Contributor
timestamp: June 12, 2017, 09:18:40 am
content: Thanks for your reply! Yeah, I'm aware that other components could be damaged as well, but with some luck it could work! Otherwise I'll just switch PCB, as there will be too much troubleshooting for what it's actually worth.. This was more of a "it'll be fun to give it a try project"Anyhow, I found a close replacement for that part now! Only need to decipher the SK 34 diode now

author: bktemp
author_rank: Super Contributor
timestamp: June 12, 2017, 09:26:29 am
content: SK34 = SK34?http://www.smc-diodes.com/propdf/SK34%20N0102%20REV.-.pdfhttp://diotec.com/tl_files/diotec/files/pdf/datasheets/sk32

author: viktor18
author_rank: Regular Contributor
timestamp: June 12, 2017, 09:36:50 am
content: The size of those diodes doesn't fit the one that I have

author: bktemp
author_rank: Super Contributor
timestamp: June 12, 2017, 09:56:09 am
content: Where is the SK34 diode? I can't see it on your picture.If it is a smaller package, SK34 is also available in SMA, often named SK34M.

author: viktor18
author_rank: Regular Contributor
timestamp: June 12, 2017, 10:01:45 am
content: Oh sorry.. I must have uploaded the same pictures twice.. I'll link it below. It's an external hard drive so this is the unit "before the hard drive" and the input is 12vhttp://i67.tinypic.com/68f1xy.jpg

author: bktemp
author_rank: Super Contributor
timestamp: June 12, 2017, 10:10:49 am
content: Yes, looks like SK34 in SMA.Search for SK34, SK34M or SS34 with package SMA (or its other name DO-214AC).They are all very similiar, only different manufacturer.

author: viktor18
author_rank: Regular Contributor
timestamp: June 12, 2017, 10:13:00 am
content: Yeah, the length was correct, but the width on the replacement is a little smaller and that's no issue. So basically found replacement for all diodes, so it's time to order them and give it a try. I can't thank you enough for your help!!

author: BradC
author_rank: Super Contributor
timestamp: June 12, 2017, 12:45:20 pm
content: Quote from: viktor18 on June 12, 2017, 09:18:40 amYou say that like it'll be easy. You'll need a board from the same drive with as close to the same batch number and firmware as you can find. You'll then need to swap over the flash that stores the adaptives, or if its internal to the mcu then you are probably completely sol unless you can find someone who has the gear to read them out providing it's not dead already.20 years ago you could just swap a board. There's a bit more to it these days. The boards have enough firmware to use the adaptives to adjust for the mechanics on the disk to read the main firmware from the service area. Without the right data all you'll get is repeated clicking as it tries to find the service area.Jump on hddguru.com and ask the experts there, you'll get a detailed rundown on what is and isn't possible, how to do it if you *can* do it yourself and probably some available nearby expert help should you want to avail yourself of it.Don't go in guns blazing and expect a positive outcome. Shorted TVS are common. Further damage isn't, and if that's what you have tread carefully.