by AltairClone » September 30th, 2017, 9:15 am
Looking at the settings sheet you posted earlier, I think I know what the problem is.
The converter regulates the 9v power input down to 5v. The receive opto uses the sending device (in this case, the Teletype's output to the converter) to provide a low impedance path to ground which allows current to flow from the 5v supply, through a resistor, through the LED in the opto, to then produce a logic transition on the output side of the opto.
However, the output of the Teletype is not a low impedance output. Between the knife-edge/wire contacts on the keyboard and the carbon wiper on the distributor, resistance in the 10's of ohms is not uncommon. This, in turn, means much less current flows through the opto LED than designed for, so the output of the opto is not triggered.
The original design of the 88-SIO board used 5v to read from the Teletype, but was later changed to over 30v (+16v to -16v) to improve reliability. 5v can be used with a different circuit design than your converter uses, but the teletype output side has too much resistance to work reliably with your converter's design.
If you can wait, I am committing to making the RS-232 adapter that simply plugs onto the J2 connector this fall/winter. No wiring, no screw terminals, no AC adapters required - just plug it in and go.
Mike