My Gigatron build

A place to eternalise your Gigatron build photos. From box to BASIC.
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james7780
Posts: 6
Joined: 11 Jul 2021, 18:43

My Gigatron build

Post by james7780 »

Here are some pictures of my Gigatron TTL build I just finished this weekend.

When the Gigatron first came out, I found it vaguely interesting, watched a few youtube videos, but never intended to build one.

But then 2 years ago I ended up with a BasicEngine kit, built that, and then this year I also built a clone Jupiter ACE (Cees Meijer's version), and then recently a friend gifted/traded me a Gigatron PCB, and it's bad form to waste an empty PCB :)

All the components were sourced locally (Cape Town). Here are the specs of my board (mostly based on which components I had already):

Clock 6.5 MHz (extra from the Jupiter ACE build).
Most IC's are 74LS. The clock "conditioning" IC (U1) is 74HCT04 and also using 74HCT377s.
Power consumption: 430mA ?

Surprisingly it worked first time when I first powered it up! However after a few minutes it locked up and now only runs for a few seconds before crashing.
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jbailey
Posts: 28
Joined: 20 Nov 2018, 08:54

Re: My Gigatron build

Post by jbailey »

Congratulation... very nice case you built too.
giobbi
Posts: 30
Joined: 11 Jul 2021, 22:12

Re: My Gigatron build

Post by giobbi »

did you find what was wrong with it?
james7780
Posts: 6
Joined: 11 Jul 2021, 18:43

Re: My Gigatron build

Post by james7780 »

jbailey wrote: 11 Jul 2021, 21:24 Congratulation... very nice case you built too.
Thanks - the case was a lot of work, but came out well.
james7780
Posts: 6
Joined: 11 Jul 2021, 18:43

Re: My Gigatron build

Post by james7780 »

giobbi wrote: 16 Jul 2021, 23:19 did you find what was wrong with it?
I actually only came right with it today, after spending weeks trying to diagnose what was wrong. I even borrowed a real Gigatron from a friend so that I could compare signals/voltages/etc.

Basically I removed all the chips, washed the board thoroughly in warm soapy water, then rinsed the board, shook the water off, forgot to rinse with IPA, and dried it with a hairdryer. Then the next day I very carefully re-inserted all the chips, making 100% sure they were properly seated in the cheap sockets.

Powered it on and it now seems to run reliably :) (I hope it stays like that).

My McPluggyFace did not work with a keyboard, so I dumped the code/data/fuse from my friend's ATTINY85 and wrote it to my ATTINY85, now it works fine :)

The only thing left to fix is the DAC (for some reason I just assumed it was a simple resistor array), cannot find that part locally.
bmwtcu
Posts: 60
Joined: 01 Nov 2018, 12:02

Re: My Gigatron build

Post by bmwtcu »

The audio DAC is an R2R resistor ladder and isn't a simple resistor array, but you can literally copy the symbol on the Gigatron schematic and build one from 10k/20k resistors. In my experience, unactivated flux is conductive, so perhaps that was the original problem you had.
james7780
Posts: 6
Joined: 11 Jul 2021, 18:43

Re: My Gigatron build

Post by james7780 »

My Gigatron is now 100% complete, here are some more pictures:
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The top of the case is a sliding acrylic panel:
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DIY ladder DAC:
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lb3361
Posts: 81
Joined: 17 Feb 2021, 23:07

Re: My Gigatron build

Post by lb3361 »

"DIY ladder DAC" :-)
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