HP97 The journey begins

[teenix]

Hi all,

I've been plodding away at the software and have made some gains.

I was purposely steering clear of the printer because it will be the first time I will have connected the print head to the driver. This is a bit worrisome because if the software fails and a head pixel stays on it will probably burn out fairly quickly.

I have monitored the output with a scope and all seems well, so then I connected some LEDs and they flashed while the line was "printed" and they all went off when the end of line marker was encountered. The motor sped up and homed the print head.

It all seemed to work so it was time to test with the head connected. The printer is a horrible thing to try and bench test with all the connections and I don't want to keep fiddling while the ribbon cable is floating around. I turned everything on, no smoke. I pressed PRx and the printer fired up but nothing legible was printed. I fiddled with the software to delay the character print start position on the paper but aside from the positioning, not much changed. I printed a long number and the printout was wider but still not legible.

I have the bench power supply current limited to hopefully avoid a mishap but should be enough to drive the heads. It may be the paper roll that is not well. Hard to say.

Anyway, I have the latest boards coming soon so that should allow me to assemble everything back into the calculator and have the printer fixed in position and lessen the chance of damage.

The new 19C CPU circuitry is much the same as for the Spice CPU board but the constant memory save at switch off was giving problems. It took a couple of frustrating days to find the culprit which was a capacitor in the print motor drive circuit. Once this issue was addressed, it started to work.

Not much to do now except wait for the boards, populate them and fingers crossed all over again :-)

cheers

Tony