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Pi T-Cobbler, 3v3 pins reading 1.6v

by linuxelf on Thu Jan 17, 2013 10:22 pm

I was just playing around with my spiffy new Pi T-Cobbler board, and noticed that the voltage drop between either of the two 3v3 pins and ground was reading only 1.6v. the 5v pins both read 5v, but the 3v3 pins only read 1.6v. I pulled the ribbon cable off, and tested voltages on the raspberry pi directly, and sure enough, there was 3.3v on both of those pins. I did a connectivity test on the various pins on the cobbler, and found that the two 3v3 pins were connected to each other, (This appears to be by design, as there are traces on the PCB connecting those pins) and I noticed that there was connectivity between all 5 ground pins (also apparently by design) but no other pins were connected to each other, and all other pins had good connectivity from the ribbon cable connection through to the breadboard connection. Can anyone help me track down what would cause the voltages to be low?
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Re: Pi T-Cobbler, 3v3 pins reading 1.6v

by adafruit_support_bill on Fri Jan 18, 2013 5:31 am

It could be a marginal solder joint on the cobbler. These can be hard to diagnose since poking them with a multimeter probe often makes them conductive. If you post some clear photos of the soldering, we'll check it over.
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Re: Pi T-Cobbler, 3v3 pins reading 1.6v

by linuxelf on Fri Jan 18, 2013 7:57 am

Oh, ok, so if it's making a very weak connection, simply attaching the probe could be enough to make the connection stronger. Makes sense. I'll go over the soldering and if I can't find what I may have done wrong, I'll post some pics. Thanks!
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Re: Pi T-Cobbler, 3v3 pins reading 1.6v

by linuxelf on Thu Jan 24, 2013 6:25 pm

I'm taking the hit for being an idiot, only because I want to spare others from this silly mistake. The problem, that was causing the 5V line to read 5V and the 3v3 line to read 1.6v with this breakout board was that the ribbon cable was attached to the Pi in the wrong direction. So, just in case you hear this symptom again, have them try reversing the ribbon cable. :oops:
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Re: Pi T-Cobbler, 3v3 pins reading 1.6v

by adafruit_support_bill on Fri Jan 25, 2013 5:53 am

Thanks for the follow up. Glad it worked out in the end :)
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