Using open collector as regular 5v output
Typical open collector led setup would be:







simulate this circuit &ndash; Schematic created using CircuitLab

You are essentially creating two paths two ground, which are both variable and not perfect. There is a C-E voltage drop as well. If you measure the output pin voltage compared to ground, when the output pin should be Low (open-collector active), what do you get? The datasheets list that max would be 0.8v. U2-U5, are they buffers? What voltage level activates the buffers? And what part number?