New project: Repro Camputers Lynx

[stephen_usher]

I'm using photographs for reference plus the PCBs then designing the case to be as close to the original as I can.

Sounds good. There's someone selling replacement case badges on eBay if you've not seen it already?

I think I'll make my own custom version with "BF Edition" added, as it's a Board Folk recreation.

[stephen_usher]

Well, the print of the top case worked.

IMG_5050.jpeg

It doesn't look too bad and dimensionally it fits the lower case correctly.

IMG_5053.jpeg

However, as expected, there are issues and this is what this first print was meant to show.

The cut-out for the keyboard isn't quite right. I've had to use a razor saw to hack it a bit to get the keyboard in. I also need to increase the height of the "skirt" as the connector at the bottom of the keyboard is fowling the chips on the PCB.

On the whole though it's not too bad at all.

IMG_5055.jpeg

The reason for the top being brown is that I've effectively run out of grey as the top case print takes about a quarter of a reel of filament.

[rubber_jonnie]

Looks good :)

How close is that to the original case in terms of dimensions and shape?

[stephen_usher]

The dimensions are based upon the PCB, which is a recreation of the original. Everything else is purely based upon pictures so it’s pretty well guesswork.

[rubber_jonnie]

The dimensions are based upon the PCB, which is a recreation of the original. Everything else is purely based upon pictures so it’s pretty well guesswork.

Gotcha :)

[HigashiJun]

Well done !

You just have to fine-tune your 3D print now.

[peters]

This reminds me. I should try kiri engineer for 3D scanning things you see if it can produce anything useful.

[stephen_usher]

The 74S03 chips arrived in the post today. They were on my door mat when I arrived home this evening.

I quickly swapped IC77, which is part of the VCAS, VRAS and SINGLESTEP circuits.

The results:

BASIC programs don't seem to corrupt any longer. Well, at least during the relatively short time of testing.

If the machine is left in the "mon" debugger the machine crashes in a similar fashion to before and after a similar period of inactivity.

So, a definite improvement.

[stephen_usher]

This morning I rejigged the CAD design, fixing the keyboard cut-out, adding supports for the keyboard posts so that the slicer doesn't generate huge supports. I also added the "vent" detail on the rear. Unfortunately I couldn't add height to the "skirt as if I did the whole model went up the creek! It doesn't really matter as the problem with clearance I was having was due to trying to use a 2 row IDC connector, the original having used a soldered cable instead.

The new print is on its way, in black this time. i don't expect the "vents" to look great as I turned off supports for the vanes so as to bring the print time down from > 12h to around 9h. This is just a test print after all.

Oh, and the swapping out of the 74LS03 with a 74S03 at IC77 has made a world of difference. BASIC programs take about half an hour to corrupt now rather than the earlier 30 seconds.

[stephen_usher]

The rest of the 74Sxxx chips arrived yesterday and I had about an hour yesterday evening to do some testing....

They've made things worse rather than better as the nearly stable system using 80ns 41256 RAM is as unstable as with 4164 chips now. Also there's a new display artefact with red "ghosting" which varies across the screen changing every 8 characters.

I'm wondering if there's some sort of capacitative coupling going on somewhere on the board, a bit like the phantom short on one of the RAM sockets which went away with IPA and a slight brush. I've noticed on some of the signals they seem to be picking up about a 0.5V echo of another signal. No idea if this is just cross-talk or something more sinister.