New project: Repro Camputers Lynx

[stephen_usher]

The sockets have arrived, so I can finish that part off.

[stephen_usher]

OK, this is as far as I can get without new supplies...

IMG_5019.jpeg

Second smoke test done and it's fine. Pulling about 500mA.

I tested the reset circuit and the first part of the clock generator by injecting a 5MHz square wave into the 74LS04 which runs the crystal oscillator and that gets as far as the 74LS161 socket. Seeing as I don't have a chip for that it can't get any further. :-)

[PhilC]

All good progress @stephen_usher. You'll be finished before you know it.

[stephen_usher]

All good progress @stephen_usher. You'll be finished before you know it.

I'll need to work out where a bodge wire is supposed to go. According to the author of Github repository he can't remember where it goes and the image of the PCB on the site is too low resolution to find out precisely. Similarly the image of an original machine on Binary Dinosaurs' site is far too low resolution to see where that particular factory bodge went.

[PhilC]

All good progress @stephen_usher. You'll be finished before you know it.

I'll need to work out where a bodge wire is supposed to go. According to the author of Github repository he can't remember where it goes and the image of the PCB on the site is too low resolution to find out precisely. Similarly the image of an original machine on Binary Dinosaurs' site is far too low resolution to see where that particular factory bodge went.

Ah, well good luck with that then. Shame that's a different layout board being the 128k version.

[HigashiJun]

OK, this is as far as I can get without new supplies...

The populated purple PCB looks awesome.

Can't wait to see the final result.

[rubber_jonnie]

Looking fabulous, I'll be happy to see it powered up :)

Funny that they got to a MK2 when the original wasn't successful.

[stephen_usher]

I think that they may have been thinking to push into a slightly more premium market with the 96K and 128K machines which, with the addition of a floppy interface, could run CP/M. 96K and 128K memory sizes were rare in '83. I'm pretty sure that they saw that the low-end was being eaten by the ZX Spectrum and they couldn't compete using a discrete chipped machine without a ULA so reduce the chip count and save production costs.

[peters]

There 128k Laureate was planned early on and I saw it at the Manchester show complete with 5 1/4 floppy drive.

I have my Lynx UG magazines as well.

[stephen_usher]

This morning I thought I'd do a bit more testing, so I put bodge wires across from the input of the LS161 to the four outputs, just to get clocks out on the other lines.

I hooked up the Owon portable 'scope as a signal generator and set it up to output a 4MHz square wave and injected that into the last stage of the LS04 on the main clock generator circuit.

Powering on the CPU didn't do anything initially until I manually shorted the reset pin... Hmm.. reset's not working... Looked at the schematic and it uses IC59, an LS09 which... isn't installed! Checked the schematic and the output of IC59 doesn't actually need to be open collector so I stuffed an LS08 in there instead and the CPU sprang to life after power on.

IMG_5020.jpeg

It's obviously now trying to run code and the ROM and RAM is being selected. However, as the chip to generate the /RAS signal isn't installed the RAM won't work, though the RAS pulses from the CPU refresh are getting through.

Anyway, looks like it's trying to work.

Increasing the clock to 6MHz, which is what the CPU is supposed to run at in the Lynx doesn't seem to work at the moment, but given how the other clocks will be very wrong without the LS161 it could be some other conflict.

Anyway, it's just a waiting game now to wait for the other chips to arrive.