By Philippe Dubois, President. Translation by Sébastien Marty.
In this eighth article, we are going to get a little more into the heart of the matter. After having studied, reverse-engineered the Micral N’s boards and even replaced some components, we are finally about to restart our unit for the first time after almost 50 years!
Indeed, the study and reverse-engineering of the boards are going well with the help of Jean-François, Sylvain and Arthur. We took out all the boards from our Micral N one by one over the past few weeks to carefully photograph and even scan them in high definition, and began to draw the circuits to document them and better understand how they work. All our work will soon be listed on a dedicated site
Analysis example of the CPU board from our Micral N
We also took the opportunity of our progress on the restoration of our unit to produce a live broadcast on the MO5 association’s Twitch channel with our friend E-Penser as a guest star, dedicated to the history of R2E and of the Micral N! The video is now available on our Youtube channel (french only) : Live sur l’histoire du Micral N.
Replacing faulty RAM chips
The RAM chips in our Micral N unit were all tested one by one!
Fortunately, we were able to find RAM chips of the same series on a famous auction site in the United States, which of course were tested on arrival. One of them will therefore replace the defective chip in our Micral N. As a reminder, these are SRAM chips (static random access memory) of 1024 bits each, so that’s only 128 bytes in total!
You can see what this historical SRAM chip from 1972 looks like by following this link.
The four 2102 series RAM chips received from the USA are all in working order!
This is good news indeed: the RAM chips we received are all working perfectly, even nearly 50 years after they were made, so we can now confidently move forward to the next steps of the restoration process.
Work session at Viveris and starting up the Micral N
We therefore organized another working session with our team of volunteers at our partner Viveris which, remember, provides the association with a fantastic electronic laboratory at their premises in Rungis near Paris. We were still in the middle of COVID, hence the mandatory mask!
The team met again at Viveris to continue analyzing the electronic boards of our Micral N
Most of the team will be able to continue studying and testing the various electronic boards of our Micral N, with the possibility, if we don’t detect any problem, to try and restart our machine for the first time! All the members present are very motivated, the atmosphere is excellent. We were joined for a few moments by a Viveris manager, curious to witness our work on the machine.
Power supply test and operation check of one of the electronic boards of our Micral N
The main electronic boards critical to the operation of the machine, at least according to our current state of knowledge, will all be checked, powered and tested one by one in order to ensure that once installed inside the frame and switched on all together, no unfortunate event occurs. Jean-François and Arthur assembled combs of the right size so as to be able to plug in each board.
Jean-François scans the chips of the Micral N with a thermal camera to check if they behave well once powered
At the end of this project, the first good news awaits us: there doesn’t seem to be any faulty board, and no component has apparently suffered from being powered up. We can put all our boards back in the Micral N’s frame and consider what’s next.
Meanwhile, Hervé and Arthur are also busy adapting a carrying case that Arthur brought, which will be large enough to safely contain our Micral N and all its accessories (plugs, cables, power supplies, experimentation boards, etc.).
Hervé and Arthur cut the foam from a large professional carrying case to fit the shape of our Micral N
We also take the opportunity to build the power cables needed to power the machine directly. It has two connectors, one on either side supplying power to half of the backplane, in order to better distribute the electrical load. This type of connector is very old and rather difficult to find these days. Luckily, we were able to find a few on the Mouser Electronics online store.
The power connectors of our Micral N are quite unusual
Restarting our Micral N!
Here we are finally! Using the laboratory power supplies available at Viveris, precisely adjusted to the operating voltages of the machine, and after we had checked one last time each electronic board individually, we decided to connect our Micral N to the mains in order to check its behavior. And there a second excellent news awaited us!
Eureka! Our Micral N powers up!
Our Micral N powers up! We are all very happy, and Sylvain is eager to confirm at last what we understood so far about the operation of this machine and the code contained in its read-only memories (ROMs). With a few manipulations, we interrupt the start-up cycle of the machine to land in its monitor, the contents of which (2 KB) was saved previously as explained in this article : https://mo5.com/en/reading-and-saving-micral-n-roms/
Since we are now relieved about the electrical start-up of our Micral N, we will be able to study very precisely how to make it run programs and start programming it! But all this will be discussed in a future article.
Until then, please don’t forget to take part in the campaign to support our work! https://micral.mo5.com
