Well I fiddled with the teleprinter some more, wondering if I could at least get it to print with just 30-0-30VDC – it needs 80-0-80. Nothing. I tried connecting directly to the relevant pins for the receiving relay but could not feel any resistance when this was applied. Odd, because I could measure its resistance with a multimeter, so what’s up.
Strangely the next time I tried I could no longer measure the resistance. Might have been me. Then it occurred to me that on the 444 everything comes out on the 50-way D connector and you can get directly at the receiver coil, and I can see the relevant ohms. So, re-wiring the lash-up and still with 30-0-30V and with a resistor in series just in case and it burst into life. Almost.
It did print, or rather tried. It got most of the letters wrong, but is at least trying. Most likely the voltage is just not quite enough, or my lash-up resistor is denying it sufficient current but I’d rather not risk the coil right now.
However, and more of a concern was that although it went through the motions, the carriage did not move. It was stuck fast and no amount of fiddling would move it. After pouring over the workshop manual there seemed to be a lever in the wrong position. Moving this freed it up and it does now move with keypresses, even though the letters are wrong.
Nearly there then… the ribbon is not rotating but there is at least one broken spring so hopefully that’s an easy fix. All I need now is a proper TU.