Having now had a chance to take a closer look at the Creed to see why when Y is sent by the TDMS it prints as Z it is clear why! The following shows why… the TDMS is sending a continual stream of Y’s and then R’s:
This is the system between characters, all is well, but…
…this should be a Y, i.e. MSMSM (M = mark, S = space), but prints a Z, i.e. MSSSM.
And the R? This should be SMSMS, not SMSSS as shown. SMSSS is carriage return, no wonder then why the typehead remains firmly at the left of the platen.
But, checking the waveform output from the TDMS shows it is indeed sending a Y, and with a good square wave. This gets rather mangled when the teleprinter receive coil is connected but still has sufficient peaks to drive the thing. So the issue is between the input to the teleprinter and the selectors.
One item to note though is the three photos above are from a video recorded on my iPhone in ‘slo-mo’ – which proved to be really very useful here!
Time to read the manual more closely…