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The Cabin >> Raspberry and Other Pies >> Got Them Fixed!
http://www.hondosackett.com/yabb/YaBB.pl?num=1413739839

Message started by Fernando on Oct 19^th, 2014, 1:30pm

Title: Got Them Fixed!
Post by Fernando on Oct 19^th, 2014, 1:30pm

Not too long ago, I threw my hat into the ring on an ebay auction for a pair of Model B Raspberry Pi's (aka R-Pi's) with broken USB Ports. I won that auction at $42 + S/H, making the R-Pi's less than $25 a piece. At the same time I bought some replacement Dual USB Ports at $1 a piece in an attempt to fix these R-Pi's and both arrived at about the same time - Wednesday (10/15/14).

That night I attempted to remove the broken USB Ports off one of them, and replace it. Well, I did not take color into consideration, as the R-Pi's USB Ports are Black and the USB ports I got are White. I also did not have all the proper tools to desolder, so it look almost 2 hours to get the job done. Eventually I replaced that USB Port on the first R-Pi, and success, it works!

Then I tried to do the same with the second R-Pi, and it did not worked. I may have used too much solder and shorted out one of the USB Pins, as the boot logs kept saying "Over Voltage on Port 2 (USB Port). So I put it aside and got the desoldering tools on Saturday (10/18/14) and then unsoldered the port off the board very cleanly and professionally. Today (10/19) I looked over the R-Pi again, checking the traces with a magnifying glass and a multi-meter, finding them OK. I took the same Dual USB Port I replaced and then removed an put it back in, being stingy with the solder this time. It now works!

So now I got two fixed R-Pi's with White USB Ports! I'll post pictures later.

Title: Re: Got Them Fixed!
Post by Fernando on Oct 19^th, 2014, 5:00pm

The one on the left is a normal working R-Pi, the middle one is the fixed R-Pi and the one on the right is the broke R-Pi before repairs; the fixed R-Pi was in the same condition as this broken one.
http://www.hondosackett.com/Fernando/R-Pis-USBs.jpg

Title: Re: Got Them Fixed!
Post by Hondo I. Sackett on Oct 19^th, 2014, 11:30pm

Awesome, Jefe! Good thinkin' addin' a board for the pi's an' such. Will try to post some of my own stuff when I get 'round to messin' with it.

~ Hondo

Title: Re: Got Them Fixed!
Post by Fernando on Nov 5^th, 2014, 11:31pm

Fernando wrote:

The third Raspberry Pi was slated as "Dead, Red LED turns On But Does Not Boot." I noticed that this Raspberry Pi was very sensitive to Under/Over Voltage but it does turn on and boot. I also noticed that it also gets very hot to the point of smelling something being burned. Voltage testing on this Pi shows that its running under voltage even though other Raspberry Pi's measured perfectly with the same power supply. It sounds to me that one or more of its voltage regulators may have been blown or shorted.

Replacing the Voltage Regulators

The repair is to find the voltage regulators that failed and replace them.

I found this article online, which explains what are the causes for a very hot Raspberry Pi, and how to test it and eventually fix it:
http://www.petervis.com/Raspberry_PI/dead-raspberry-pi/dead-raspberry-pi.html

More detailed information from his site:
Main Regulator - NCP1117-3V3 in a DPAK case 369C
http://www.petervis.com/Raspberry_PI/dead-raspberry-pi/NCP1117-3V3-pinout-RG2-pinout.html

1st Secondary regulator - NCP1117-1V8 comes in a SOT-223 case
http://www.petervis.com/Raspberry_PI/dead-raspberry-pi/NCP1117-1V8-pinout-RG1-pinout.html

2nd Secondary regulator - LP2980-2V5 is a SOT-23 regulator in a DBV0005A style package
http://www.petervis.com/Raspberry_PI/dead-raspberry-pi/LP2980-2V5-RG3-pinout.html

I seen that Mouser.com has these regulators at relatively inexpensive prices. I need to search digikiey.com and newark.com to see if they have them and for how much. If replacing these three regulators fixes the over heating problem as per the article's description, then I have solve the issue and could possibly fix more Raspberry Pi's.

In seeing this, I can speculate that replacing all three regulators at once would be the best option, though replacing the main regulator should fix it.

The point is this as I see it, if the Raspberry Pi turns on with a red LED but does not boot with a known working SD and a known working power supply, then its voltage regulators need to be replaced.

I'll see about getting these voltage regulators and fixing this one Raspberry Pi that gets very hot as soon as I can and post my results here.

It's been 2 weeks and yes, I did get the voltage regulators for the R-Pi. I found that Regulator 3 (the tiny one) fell apart when I put the desoldering iron to it, while Regulator 2 (the largest one) had problems trying to remove it off the board since it's back was soldered to the board. In replacing Regulator 2 it was either damaged from the factory or I damaged it soldering it to the board; either way it was replaced again.

Now the R-Pi runs cooler than before but it still heats up, and something is pulling it's main voltage down. I'm eyeing Capacitor C5 (on the board, C6 on the Schematics) as possibly shorted out. Replacing that should fix it.

R-Pi with regulators removed and replacement regulators RG-1 and RG-2 ready to go in:
http://www.hondosackett.com/yabb/R-Pis/IMAG0128.jpg

R-Pi with regulator RG-1 (the medium sized one by the GPIO) soldered in:
http://www.hondosackett.com/yabb/R-Pis/IMAG0131.jpg

R-Pi with regulator RG-2 (the large sized one by the capacitor and micro USB Power Port) soldered in:
http://www.hondosackett.com/yabb/R-Pis/IMAG0133.jpg

Title: Re: Got Them Fixed!
Post by Hondo I. Sackett on Nov 9^th, 2014, 11:55am

nice, likin' the hardware issue tips an' fixes I'm learnin' from this.

Title: Re: Got Them Fixed!
Post by Fernando on Nov 11^th, 2014, 9:46pm

The weak point with the Raspberry Pi's is the GPIO. In the GPIO are 5V and 3.3V lines for added boards. But at the same time some boards have their own power supplies, most of the time unregulated. Then connected to the Raspberry Pi and both had power, would create a surge within the Raspberry Pi and fry it. In the last case the regulators went out and a couple of capacitors (which are yet to be replaced). This is because the Power Supply Unit in the Raspberry Pi is Linear, not Switching.

The Model B+ has a better Switching PSU, but the GPIO is still a weak point where added voltage can surge through the R-Pi.