meeotch
Posts: 8
Joined: Sat Jun 08, 2013 9:46 pm

D17 replacement

Sun Jun 09, 2013 7:22 am

After accidentally forgetting to change the voltage on my universal DC power supply (note to self: next time, just buy a dedicated supply, you cheap bastard), I was rewarded with a little puff of magic smoke from somewhere in the neighborhood of my Pi Rev. B. It still boots, and I haven't found any issues with it running - but the D17 TVS diode gets super hot, and its package looks like it has a hairline crack in it.

I thought I might try replacing D17, in an attempt to be green and salvage the Pi. It looks pretty easy to solder. Does this seem like the correct replacement part?

meeotch
Posts: 8
Joined: Sat Jun 08, 2013 9:46 pm

Re: D17 replacement

Sat Jun 15, 2013 2:44 am

Replying to myself, in case it helps anyone. Yup, it seems to have worked. The Pi boots, anyway, and nothing seems amiss. The replacement diode is cool as a cucumber. Will have to wait and see if I damaged anything else - I'm certainly not going to attempt overvolting it to see if the new diode is effective protection, though. Cost: just $0.45 and a little bravery - not bad.

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Tage
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Re: D17 replacement

Sat Jun 15, 2013 3:46 am

the replacement should work fine. as you already noticed. you could even have removed the old part and not bothered to add a new one unless you think you need the protection. the main function is to protect against too high voltage in cases like this.
the most sensitive part seems to be the IC2 controller which is intended for 5V voltage. I was not able to find a maximum rating but it can probably take about 7V before failing.
the main concern (if the Pi is still working and IC2 is not smoking) is that the capacitor C6 might be damaged which is uncommon as it has a 16V rating. the next possible victims are the 3.3V and 1.8V regulators RG2 and RG1. these have 20V ratings, so no worry there. RG3 is the 2.5V regulator which is more sensitive. it has 16V rating.
the other components which are subject to over voltage in this case are all ceramic capacitors and these are tough and normally can take a lot of abuse. one possible weak link is C32 which is a yellow 47uF tantalum cap. I was not able to figure out the marking on this one but my guess is the "J" stands for 6.3V rating. if it fails it would probably be cracked and shorted so the Pi would not work. I think some people would like to see a much larger capacitor for C32 to make the Pi less sensitive when plugging in USB.
if the Pi appears to be functioning there should be nothing to worry about. you could measure the voltage across C6 to make sure the F3 fuse is healthy. the voltage across C6 should be well above 4.75V.

drgeoff
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Re: D17 replacement

Sat Jun 15, 2013 1:44 pm

I wonder why the designer choose the bidirectional version of this diode. At least one person has posted here of damaging his RPi by applying reverse 5 volts (+ and - swapped over) to the micro-USB socket. The unidirectional diode would probably have saved him.

meeotch
Posts: 8
Joined: Sat Jun 08, 2013 9:46 pm

Re: D17 replacement

Sun Jun 16, 2013 12:49 am

@Tage - Thanks for the reply. I should have mentioned that the original voltage screw-up was 12V - so it sounds like most of the components you mentioned are safe. (I assume if IC2 were fried, I'd know. Not knowing its function, but judging by its size & shape that it's probably important.)

C6 shows 5.05V across with nothing attached (including SD card), 4.84V with an SD card, and 4.78V with wifi dongle. F3 is showing about 85mV drop. Seems reasonable, and so far no weird behavior.

I did manage to corrupt my filesystem while measuring the above voltages somehow - probably by yanking the power without shutting down. Sigh.

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Burngate
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Re: D17 replacement

Sun Jun 16, 2013 9:41 am

meeotch wrote:... (I assume if IC2 were fried, I'd know. Not knowing its function, but judging by its size & shape that it's probably important.)...
http://www.raspberrypi.org/wp-content/u ... .2_027.pdfI think IC2 is quite important. It's the SoC

meeotch
Posts: 8
Joined: Sat Jun 08, 2013 9:46 pm

Re: D17 replacement

Sun Jun 16, 2013 4:58 pm

I figured as much... Had to be that or IC3. Looking at the schematic now, it's interesting that IC3 is just USB/ethernet. I guess size only matters so much. That's a relief! ;-P

Magillus
Posts: 1
Joined: Sat Jul 20, 2013 10:13 pm

Re: D17 replacement

Sat Jul 20, 2013 10:16 pm

This topic helped me, I had some similar issue, I had 5V regulated connected to USB and to GPIO (same source) it burned that D17 - not sure why, voltage was 5.04 V.
I removed burned D17 diode and board works - let see how long.

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