As stated on:
http://www.hondosackett.com/yabb/YaBB.pl?num=1413989311/5#5 Quote:Issues Continued - Voltage on Model B.
Recently I obtained another Raspberry Pi from ebay. Its former owner stated that the green light would flash and not boot. I read that this might be problems with the SD Card holder, so I ordered a couple of those as well to fix the Raspberry Pi.
So I tried it, it would not boot. The green LED turn on and stays on, but the red LED flashes. According to the pattern of flashes, it could mean file corruption or file(s) missing from the SD. But at least it turns on and flashes. With a multimeter I checked out traces and connections and they were fine. But then I checked for voltage, it failed. Putting the multi-meter on 10 volts, I measured across T1 and T2 to get a voltage (see pics) and I got 3.25 volts. The normal is supposed to be between 4.75 volts and 5.25 volts. I did a few check and then turned on the Raspberry Pi. It eventually turned on and booted with a low voltage. I then connected it to my monitor with the HDMI adapter, and it failed - back to that flashing red LED.
http://elinux.org/images/thumb/8/8c/Voltmeter.JPG/250px-Voltmeter.JPG http://elinux.org/images/thumb/d/d1/RPI_Test_Points.JPG/400px-RPI_Test_Points.JP
G I thought about it for a while. I'm using an USB extension cable on top of the tiny 3ft USB cable with the micro connector to make it reach to my monitor cable. Also, the HDMI adapter steals power in order to do the conversion to VGA. So I managed to shift a few things around to get the cable to reach, barely. It manages to turn on and boot. But plugging in an Apple Mouse got me a dead mouse. Plugging in a small PC Mouse I bought for the PIs, it works. Measuring the voltage across T1 and T2 gave me 4.5 volts, just failing but just barely.
This Model B works, despite what the person who sold it to me said on ebay. It's that it is sensitive to under voltage. Once the voltage goes under 4.5 volts, there is problems. I also noticed that it gets hot, a sign of under voltage/amperage. The Model B needs a steady 5 volts at 1 amp minimum. But over voltage or over amperage would damage the Raspberry Pi.
I'll continue on seeking a solution to this problem though the solution is to have a rock-stable power supply and proper wiring. Thin USB Cables can cause problems as it can limit the flow (amperage) to the Raspberry Pi from the Powersupply.
I just got a 5ft USB to USB Micro cable, which happens to be a bit thicker than the 3ft cable I got with the Power Supply with the Raspberry Pi. As first thought, it works, though I still need about 6 or more feet of cable, it being thick allows more current and more power the Raspberry Pi.
With the 3ft cable, I see the power LED flicker, dim and brighten. With this new 5ft cable, the power LED is bright and steady. With the "Broken Pi" it turns on and boots with no issues, though I felt the heat sinks on it get hot. There might be a short on the board or some other issue I have to investigate. But it runs without problems!
Right now I'm transferring ROMs to PiMAME on one of the Raspberry Pi's with a repaired USB Port, using a 1-to-4 USB Hub and a USB Drive. No other issues seem to be apparent. After testing the ROMs, the next test is to test the Raspberry Pi with an Apple Keyboard and Mouse and see if it still works or crashes. But thus far things seem to be OK.
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Power Issue on Raspberry Pi Model B's (Read 400 times)
