Ok so I adjusted the teleprinter’s transmitter to the correct tolerances and made matters worse! It was at least trying to send characters out in response to key presses even though they were all wrong. Now it sends fewer, i.e. some keys send nothing at all, but still equally wrong! I can’t see how I made it worse by correcting it.
But it’s interesting delving into this beast. The transmitter itself is simply a series of contacts. The selector mechanism pushes on pins which push or leave the code bits, and these are then read by another set of contacts which fire in sequence to send the relevant word. But it would be nice if it worked…
So I thought it might be an idea to get a meter on to each code contact to see if it was connected to mark or space when a key was pressed and the mechanism moved appropriately. Nothing. Ok… take the transmitter out again. It does not match the wiring in the book. The book / manual says that each code contact comes out on pins A1 to 5 but they aren’t. There is no wire on A5 and in each case the code tongue is wired directly to the associated readout contact. There should be 18 wires on the plug – there are only 10. However, the change to the wiring should still work as the interconnections are essentially the same as would have occurred if wired according to the diagram.
Update: after a lot more adjustment, taking it somewhat outside the design specification I can now semi-reliably generate the correct codes per key press. The machine skips sometimes, which needs sorting and it does not always generate a character, but when it does manage it is generally the correct one. So, some progress. Turning the machine by hand and checking each code contact does reliably get it right, just not at speed under motor control. Some further adjustment should cure this but I am concerned that the clearances are now a bit off from spec, as when in spec nothing worked at all.
I am going to concentrate on why it will not receive properly when given a decent signal. At least that way if I can eliminate at least one of the two faults I’ll be happier. Meanwhile the machine continues to migrate between the shack and the workshop, which is a trip of two flights of stairs and three doorways. But I am getting some exercise so no bad thing!