HP97 The journey begins

[teenix]

Hi all,

Well, I thought the light at the end of the tunnel was glowing but it faded again.

I was assembling the 2 circuit boards as would be done when closing the 2 case halves together to check the alignment of the connector pins, and they mated quite well. Unfortunately, the print head ribbon where it plugs into the socket was interfering with the side of the case, only by a millimeter or two, but enough to cause a problem. On looking closer at the original printer ribbon connecter, it is indeed a bit narrower than the one I sourced. The circuit board is only about 5mm wide here so there is not much wiggle room, but with a bit of fiddling, I was able to get around it.

After that I could close the two halves further but not the full way. Also, I noticed that the ribbon cable that attaches the keyboard to the CPU board needs to be a certain length, or the display connecters contact the key board traces and cause shorts. My new ribbon cable is a bit longer, but I was able to adjust it to match the original.

I thought clearing these hurdles would finally allow the halves to close properly, but no. I'm really getting a feeling for what the engineers were dealing with when working out the construction details for this little beastie.

I used surface mount parts on the board which are much smaller than the original, most notably in height above the circuit board. This, I thought, would provide ample clearance for final assembly, but (of course) nope.

If you look at an original CPU board in the image, you'll see there are no parts on the lower end of the board. This is probably not something that anyone would notice, I certainly didn't, but there lies the problem. Even with the surface mount parts, the two calculator case halves will not quite fit together, that's how tight the space is in there, mostly because of the bottom of the battery compartment and there are also a few tiny protrusions molded in as well adding to the problem. The case can be closed but the last few mm needs a small amount of pressure which I don't like.

Unfortunately, this means another board re-design :-(

Some good news, I sorted out some printer code issues which now seem ok. I still haven't switched the head driver code on, leaving that till last, but I can see the motor speed ramps up after the characters are "printed" as the head continues on and homes. I bought some new paper rolls, but they were too wide. I didn't notice the 37mm rolls referred to the diameter not the width - sheesh.

I was also able to run a program which loaded new program and data files from memory during execution. The battery-less Continuous Memory is also working.

So close this time....

cheers

Tony