The only way to find what was wrong with the tab interposer operation was to get access. I had to remove the mainspring and other parts yesterday, but that had to continue to take off the entire return/escapement pulley assembly with its large plate that sat in the way of everything.
|Improved access. The green oval indicates the CR and index latches, the red oval is for space, bs and tab.|
|Bent spring for tab interposer is visible in the center|
I was able to extract the old spring and work out where the substitute will connect. It will be challenging but possible. I began looking through my 17 plastic parts bins and several large boxes of typewriter parts, but a first look didn't turn up the right spring. I need something with about 18 tight turns, good tension and perhaps 5/8" or 3/4" loose length.
I found a suitable spring and invested an hour trying to hook the far end into the interposer eyehole deep inside the mass of levers, brackets and springs. It will be relatively easy to hook the near end, but it is contingent of first attaching the far end.
I did more work on the carrier return mechanism and now have it springing back to full rest position when it is released. Tentatively, the problems are corrected, although to be sure I have two tests to perform - CRs from the Return button while under power, and CRs initiated by a program. In the same way, I will need to verify tab, space, index and backspace by program control and the Tab and Space buttons as well.
I tried for another thirty minutes as night arrived, but still haven't hooked the far end of the spring on the tab interposer.