Definitely something flakey with the I2C on Netduino. It seems to stop (SCL/SDA locked high) at the drop of a hat.
I can reproduce this simply by connecting my Fluke DVM or Scope probe (1M, 100pF) onto the SCL line (it survives SDA probing). Hooking SDA/SCL into a P82B715 also kills it.
I love my netduino but I need reliable I2C. May need to change hardware if there is no fix for this soon (Hope its not a Netduino board hardware layout issue!).
@Tony,
I've also experienced this where SCL/SDA are locked high.BTW, which Netduino board are you using?
Currenlty I don't have the possibility to send a photo but, I'm using a breadboard to test all and the 'cables' are about 10 cm (cables used to connect the SDA/SCL to the PCF8574, all others connections are made with breadboard jumper).
I have used two 4.7 Kohm resistors (pull-ups to +5V) connected the SDA/SCL of the PCF8574N. All the connections are made on a breadboard and I'm using the +5V directly from the Netduino.
Edit: I have added a sketch of my test condition:
@Gigios, do you have a scope?(you can use an arduino as a basic scope and/or logic analyzer). Also, at the very least, when your device doesn't work, can you put a multi-meter on the SDA/SCL lines and see if they are high or low?