Oscilloscope or logic analyzer can't connect to SCL line of sensor MPU650 GY521


I have a gyroscope (MPU-650 on GY-521) connected with an Arduino Uno. The sensors works fine and I wanted to "sniff" the I2C data using a logic analyzer (ScanaQuad 100). This works if I only attach a probe on the SDA line and connect to GND. When I try to connect the SCL probe the sensor stops working.

For error searching I used an oscilloscope. Connecting to GND and SDA line works perfectly and I can see digital signals and measure 3.3V. Also there I have same problem that when I connect a probe on SCL line, the voltage drops to mVolts and stops working.

As an electronics newbie I would appriciate some advice on how to deal with this and possible explanations. I bought the logic analyzer and oscilloscope to learn more about electronics and to aid in error searching. Now these tools are part of my "challenge" and learning curve.

Best regards,


There must be something wrong with the clock-line. Try both A4,A5 as digital outputs and send alternating 1/0. If your scope still ruins the signal, a pin may be damaged.

... To check for current : toggle them slowly with a LED and 220R connected. Try LED with anode/cathode switched

Have you got pull up resistors on those I2C lines? It sounds like you may not have.

I tried testing the pins as suggested and it turns out that the board is the problem. After some hours the Uno "died" and I couldn't upload sketches anymore. I also tried to see if I could reach it using an Atmel ICE programmer but there the deviceID can't even be read anymore and a got a failure telling that it wasn't able to set it in programmer mode.

Thanks for the tips!