This calculator has an ALPS plotter mechanism. The original pens aren't available any more, but you can buy some expensive new ones of a slightly different design. Or you can attempt to make a pen out of a holder and a chopped down ballpoint refill.
From some brass rod I machined a holder which is the same shape as the pen, with a hole at the front which will hold a ballpoint refill.
It fits in the plotter:
The refill used turns out to be critical to the functioning of the pen replacement. If the tip is too wide then it simply won't fit through the hole in the sheet spring in front of the pen holder. If it's too small then it has no spring action. The first refills were too big, the second set (0.5mm I think) were a bit small but worked.
The holder jams now and again, but does write successfully.
I now have quite a few instruments for electronics, some scopes a logic analyser and a thurlby multimeter/serial analyser/scope. the end of the workbench now has a gap after the shelves were built, and I was going to fill it in with a piece of worktop. Then I measured the instruments and found that they all fit in the gap. So, after a quick bit of wood bashing:
I have used some scrap wood and old flooring and made a simple rack for the equipment:
The rack is on wheels so can be moved about. I am hoping that the space freed up on the workbench will be more than I would have gained by filling the gap where the rack sits with more worktop. I think it will as I can have the logic analyser and scope next to something I'm working on and take up no bench space. We'll see.
As it's made of scrap wood, I could just dismantle it if it doesn't work out.
One circuit of a pod and some routing and we have a pod for the LA4800:
It's a bit big as I just wanted to see if the circuit was correct and I anticipated lots of scoping. As it turned out the only problem was the transistor pinouts and the orientation of the pod cable sockets. Neither of which is much of a problem. as the pod works.
Here's a quick trace of some signals on the Epson HX-20 IO port.
The analyser works perfectly as far as I can see, apart from the display problems, which really are a shame.
I had to solder wires on for this test as the clips I ordered haven't arrived yet, but that's fine.