Checking that the Micral N is working properly and starting up for the first time

By Philippe Dubois, Chairman.

In this, our eighth article, we're going to get a little more to the heart of the matter, because after studying and reverse engineering the Micral N's boards and even replacing a few components, we're finally going to get our example up and running for the first time, almost 50 years later!

Indeed, the study and reverse engineering of the boards is well underway with Jean-François, Sylvain and Arthur. We've taken all the boards out of our Micral N one by one over the past few weeks to take careful photos, or even scan them in high definition, and start drawing the circuits to document them and better understand how they work. All our work will soon be referenced on a dedicated website.

Exemple d'analyse de la carte CPU de notre exemplaire de Micral N

Example of an analysis of the CPU board in our example of Micral N

We're also taking advantage of the progress we've made restoring our copy of Micral N to produce a Live on the MO5 association's Twitch channel with our friend as guest star. E-Thinkdedicated to the history of R2E and Micral N! The video is now available on our Youtube channel: Live on the history of Micral N.

Replacing faulty RAM chips

Thanks to the device that Jean François created especially for dumping ROMS and testing the very old, specific RAMs in our Micral N, we were able to determine that out of the dozens of chips in our machine, only one was defective! This is in stark contrast to the poor quality of the more modern RAM chips found in contemporary 8-bit microcomputers of the 1980s.
Les puces de RAM de notre exemplaire de Micral N sont toutes testées une par une !

The RAM chips in our copy of Micral N are all tested one by one!

Fortunately, we were able to find RAM chips from the same series on a famous auction site in the USA, which were tested when they arrived of course, and one of which will replace the defective chip in our Micral N. As a reminder, these are SRAM (static random access memory) chips of 1024 bits each, or just 128 bytes!

You can see what this historic 1972 SRAM chip looks like by following this link this link.

Les 4 puces de RAM de série 2102 reçues des Etats-Unis, toutes fonctionnelles !

The 4 2102 series RAM chips received from the USA, all functional!

The good news is that all the RAM chips we received are perfectly functional, even almost 50 years later, and we can now move ahead with the rest of the restoration of the machine.

Work session at Viveris and start-up of Micral N

We are therefore organising a new work session with our team of volunteers at our partner Viveris, who we would like to remind you is providing the association with a fantastic electronic laboratory at their premises in Rungis in the Ile de France region. We're still in full COVID mode, so masks are compulsory!

L'équipe se réunit une nouvelle fois chez Viveris pour continuer d'analyser les cartes électroniques de notre Micral N

The team meets again at Viveris to continue analysing the electronic boards of our Micral N

Most of the team will be able to continue studying and testing the various electronic cards in our Micral N, with the possibility, if we don't detect any problems, of trying to get our machine up and running again for the first time! All the members present were highly motivated, and the atmosphere was excellent. We were joined for a few moments by a manager from Viveris, who was curious to appreciate our work on the machine.

Test d'alimentation et contrôle de fonctionnement d'une des cartes électroniques de notre Micral N

Power supply test and functional check on one of the electronic boards in our Micral N

The main electronic cards that are important for the operation of the machine, at least in our current state of knowledge, are all going to be checked one by one, powered up and tested, to ensure that once they are in the chassis of the machine and powered up all together, nothing untoward happens. Jean-François and Arthur have made combs to the right size so that each card can be plugged in.

Jean-François passe à la caméra thermique les puces du Micral N afin de vérifier le bon comportement une fois alimentées

Jean-François uses a thermal camera to check that the Micral N chips behave correctly when powered up.

At the end of this project, the first piece of good news is that there are no problematic cards, and no components have suffered from being powered up again. We'll now be able to put all our cards back into the Micral N chassis so that we can look ahead to the next stage.

In the meantime, Hervé and Arthur are also busy adapting a carrying case that Arthur has brought back, which will be able to safely contain our Micral N and all its accessories: plugs, cables, power supplies, experiment boards, etc.

Hervé et Arthur découpent la mousse d'une grande mallette de transport professionnelle pour y adapter les formes de notre Micral N

Hervé and Arthur cut the foam from a large professional carrying case to fit the shapes of our Micral N.

We also took the opportunity to manufacture the power cables needed to supply the machine directly. The machine has two connectors on either side, each feeding one half of the backplane, to distribute the electrical load more evenly. This connector is very old and it's rather difficult to find one these days. Fortunately, a few have been found on the Mouser electronic components website.

Les connecteurs d'alimentation de notre Micral N sont peu conventionnels

The power connectors on our Micral N are unconventional

Our Micral N is back in action!

Here we are at last! With the laboratory power supplies fitted to Viveris, carefully adjusted to the machine's operating supply voltages, and after a final check of the electronic boards one by one, we decided to electrically connect our Micral N in order to verify its behaviour. And that's the second piece of excellent news!

Euréka ! Notre Micral N s'allume !

Eureka! Our Micral N lights up!

Our Micral N lights up! We're all very happy, and Sylvain can't wait to finally check everything we've understood so far about how this machine works and the code contained in its ROMs. With a few manipulations, we interrupt the machine's start-up cycle to arrive at its monitor, the contents of which (2 Kb) had been saved previously, as seen in the article : https://mo5.com/lecture-et-sauvegarde-des-roms-du-micral-n/

Now that we've been reassured about the Micral N's electrical operation, we can take a closer look at how to make it run programs and start programming it! But all that will be covered in a later article.

In the meantime, please don't forget to take part in the campaign to support our work! https://micral.mo5.com