Uh Oh.Electron inbound

[alexh]

Out of curiosity what expansion(s) do you use with your Acorn Electron?

[rubber_jonnie]

Out of curiosity what expansion(s) do you use with your Acorn Electron?

I have an ELK SD64.

[stephen_usher]

Here's a video on the Mogway Elk ULA

[rubber_jonnie]

Here's a video on the Mogway Elk ULA

Interesting watch, looking forward to getting mine.

[rubber_jonnie]

How exciting! Mogwaay's ULA replacement is nearly here and should arrive tomorrow

I'll also start getting together the parts for Budgies ULA replacement soon too now that I have the main IC, but that's a slightly harder project.

Should be interesting

[stephen_usher]

[rubber_jonnie]

OK, so the ULA replacement from mogwaay arrived today. I opted for a partial build and once again had to deal with components the size of a speck of dust!!

This is what I received:

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And after fighting with the really small things for a bit, I got all the necessary parts including the main IC installed. I'm pretty happy, the IC went on first time in the right place

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After a check of the pins, only one pin hadn't soldered down so I quickly fixed that with my iron and it all looks good. The bottom board passed all its tests and now I just need to join the boards together, but I'll do that once I've checked the main IC for shorts across the pins.

[stephen_usher]

I hope that you don't have hay fever at the moment with those tiny resistors.

[rubber_jonnie]

I hope that you don't have hay fever at the moment with those tiny resistors.

No, I was fine today despite the high pollen count!!!

I think because the board is quite thick, I had a lot of problems using the technique I used on my Analog V2's, which was solder one end then settle the resistor down before soldering the other, but the thermal mass just seem too much, so in the end I tinned the pads, used thick flux to hold the parts in place and used hot air at a slow speed to solder them down. That worked a treat in the end.

I've been through and checked for shorts on the main IC and there are none, and no loose pins, so the whole thing is assembled now and awaiting flashing. I managed to get the harness for the serial adapter built too:

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But I need to figure out how to flash it as I can't see any pre-made firmware. Too tired to try and figure it out now, so a job for tomorrow I think.

[rubber_jonnie]

OK, so this Elk is finally fixed!!!

And no, it wasn't the ULA after all, but the ROM!!!

Having built and programmed the ULA replacement, the machine still didn't work, so I pulled the ROM and socketed it, and when I swapped in the ROM from my spare issue 4 board, this happened:

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OK then, so I tried with my ElkSD attached and got this:

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And this:

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All using this:

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Putting back the original ULA:

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It all worked just fine:

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So on to the culprits:

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First off, the CPU was one I'd fitted previously and as it was new, I expected it to work, it didn't. Then the 2 RAM ICs I found bad after removal and replacement with known good.

Finally the ROM. Mask ROMs rarely go bad, but this one did. I was able to read the working ROM from the iss 4 machine with my TL866, though I had to disable chip ID and pin detection for it to work, but it read as a 27C256.

I then wrote that to a replacement 27C256 and that works perfectly in the Elk

I did read the faulty ROM, but all it came back with was 80s and 00s, so no wonder it didn't work!!!

Whew, that was quite the journey.