Fixing and upgrading an Enterprise 64

[PhilC]

I've just replaced the video oscillator for one I took out of a spectrum PCB that's on the spares pile. Now to get the video sync to work correctly I have to set a VPP of around 0.8V on C43.

I think the stuttering may actually be video related and not CPU related as I had thought earlier.

I think I'll need to check the LM1886 & 9 datasheets to see what it's expecting. but so far on the boot screen its rock solid (did I speak too soon again?)

[PhilC]

It does seem to be working a lot better now since I've changed the video crystal. It's now actually quite difficult to measure the VPP on C43 as doing so with my oscilloscope even on 10x causes the sync to distort due to adding the little bit of extra capacitance. You can also do the same by sticking your fingers on the clock pins so I've just tweaked it by"eye" shall we say and so far it seems to be working. Before it would have started glitching after about 10 mins runtime. So far we've gone 30 mins.

[stephen_usher]

Fingers crossed!

[PhilC]

And 90 mins later it's still working, so I am now more than happy to build the ram and floppy boards when they arrive, knowing that any new faults will be due to them (hopefully none).

@stephen_usher fingers crossed for the upgrades as well. Will have to pinch your hotel &floppy STL file too soon then

[stephen_usher]

I'll package up and publish the designs next week.

[PhilC]

I'll package up and publish the designs next week.

Cool, thanks very much.

[PhilC]

And it worked straight away when tried earlier, so I've tempted fate and put the screws back in the case and it back on the shelf till the PCBs arrive

[PhilC]

The ram and floppy interface PCBs have arrived today.

PXL_20260805_200008359.jpg (240.09 KiB) Viewed 32 times

I should have all the parts to build both boards but will likely start building the ram board first.

[PhilC]

And that's the ram upgrade installed.

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It was actually pretty easy to install. I'd initially joined everything up with headers but due to space constraints I've soldered the EXP2 connections directly to the headers on the ram board and used round pin headers for the ram board to EXP1 connection, which is removable if required.

Next up is to build and test the floppy board but that's going to take a bit longer.

If anyone is interested, I used this ram board.

https://github.com/StupidHumansInc/EP_RAM

[PhilC]

And finally the screws are back in and the 3d printed heatsink cover is fitted.

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I used my new FDM printer for it rather than the resin one, so far so good, other than it being a little too shiny black.