Posted by Evan Slatyer on October 6, 2014 at 9:04pm
A curious problem here. I'm not getting any power on the PX4IO ACC_POWER_5V rail, which is necessary for powering the 3DR radio.Here's the system setup:PX4FMU v1.7PX4IO v1.33DR GPS + compass module (GPS plugged into FMU GPS port, compass plugged into FMU_I2C3 port on the PX4IO)3DR 900MHz radio (plugged into FMU_USART2 port on the PX4IO)Sparkfun MAX3232 breakout to talk to another onboard computer wired into FMU_USART1 TX/RX, GND, and 3.3V on the expansion connectorUS Digital MA3 encoder wired to FMU_USART2_RTS, GND, and 5V on the expansion connector (code modified to use the FMU_USART2_RTS pin as PWM input)Honeywell HSCDRRN001ND2A5 pressure sensor wired to FMU I2C3_SDA/SCL, GND, and 5V on the expansion connector, via a Sparkfun bidirectional I2C level shifterPower via a 15V bench power supply for now.This was all fine last week. However, today I found the 3DR radio unresponsive - no lights when power was supplied. Everything else was fine, and when the radio was plugged into a computer via USB it was fine too. A bit of checking showed that the 5V supply for the 3DR radio was not working, and I traced that back to U5 on the PX4IO (the current limiter for 5V accessories).What I've tested:VDD_5V at the expansion connector: 5VInput to ground on U5: 5VOutput to ground on U5: 0.05VEnable to ground on U5: 5VOvercurrent to ground on U5: 3.14VAs far as I can tell, this means that it's getting power, enabled, not over the current limit (the overcurrent pin output is open drain) and not outputting anything. Removing the PX4FMU, 3DR radio, and compass (so the only things plugged into the PX4IO were the power supply and arming LED/button) did not change the results.I thought it might be one of my modifications, but those were all done on the FMU (there's nothing unusual plugged into the PX4IO) and the ACC_POWER_5V rail is not connected to the FMU.Any ideas? At the moment I'm planning to try to swap the failed chip with one of the other AP2151 chips (that supply the never-used accessory power ports), but there's not much point doing that if I'll blow the new one up too.Cheers,Evan
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