Fun fact: Very early Macintoshes were quite hackable, and plans for hacks like this were frequently done. There was even a kit someone made that added SCSI to the original Macintosh (basically duplicating circuitry from the Macintosh SE). That kit required soldering wires directly onto the CPU pins.
It is worth mentioning that hacking those machines is much more accessible today than it was 30 years ago. While Adrian's modification was mostly period correct (down to the schematics that he was using), he stumbled across an error in the schematics that he was able to verify with a modern oscilloscope. While equipment with similar specifications would have existed back in the day, it wouldn't have been affordable to a hobbiest (even a semi-professional one) working from their basement.
Old electronics is fun simply because what was once cutting edge is now available to a wider audience.
He only used the scope to look for activity on the pins; he did not really rely on any of its "modern" features. His mod was well within the capabilities of the home hobbyist at the time. Swapping DRAM chips around was a well trodden path.
I think it's probably more important to note that a 4MB SIMM would have run close to $200 at the time this was all current hardware.
Perhaps there were other ways to see whether there was activity on the bus, but I was thinking of having a scope that was useful for the 8 MHz bus speed. Yes, they existed. On the other hand, they were not affordable for most people.
And yes, memory was expensive back then. I remember spending several hundred dollars to get 16 MB in 1992. That purchasing decision biases my computer purchases to this day. I still over provision RAM after reaping the benefits of it over 30 years ago.
There are a number of ways to probe a data bus for the presence of a signal. You don't need a scope capable of fully characterizing it to know it's there.
And furthermore it wasn't difficult or expensive to get ahold of a 10 year old scope in the 90's; it just took slightly more effort.
I think as well about people who created accelerator boards, and recreated the functions of the logic board at various levels of sophistication. There are (I think) 68030 upgrades to the original Macintosh Plus, for example, that add RAM way beyond the wildest dreams of any owner back then.
I think the greatest achievement here was was the Radius Rocket Stage II, which was essentially an entire logic board on a NuBus card that claimed to System 7 to be a Quadra 950, but was essentially a diskless, portless Mac that could
be run independently of the host system!
Just to be clear (and this is also said in the video): the Mac classic could of course be equipped with 4M RAM through an expansion card. What was done here though is a direct replacement of the soldered-on RAM chips on the board itself with bigger ones, and this can be made to work by actually removing the CAS PAL and a few botch wires (though the soldering of these RAM chips is not for the faint of heart, so this only really makes sense if the PAL chip has a defect and needs to be removed anyway, or if you want to build a Mac classic with 4M and a very small footprint).
In this case it was because of a defective 74LS174 chip. To be more accurate, he was experimenting with a doner board since it's 74LS174 was used to repair another machine.
I think the actual application in this case was education, likely for himself but interesting enough for his audience.
Adrian Black's channel has gone through interesting transitions through the years. He went from an everyday hobbiest who made simple, but common, repairs to someone who tries to understand how the electronics works to diagnose problems and make targeted repairs. While the host of some channels will say, "old caps, let's replace them," Adrian will see if the caps are actually source of the problem before replacing them (unless they are of a type guaranteed to leak or explode). Rather than swapping chips, he will look at the signals generated by the chips to see whether they (or surrounding circuitry) are the source of the problem.
Why is experimentation like this valuable? I would suggest there are two reasons. First of all, people should be encouraged to experiment with what they have. While Adrian has a lot more than most people, his resources appear to be limited (and a lot of his more exotic stuff appears to be the product of goodwill, since people appreciate what he does). Second, it lays the foundations for projects that may have more utility. For example: much of this particular journey would be applicable to expanding the memory on machines that don't have an integrated way to expand memory. (Say you wanted to upgrade the RAM on a Macintosh 128k.)
I was confused by the headline, because my own Macintosh Classic has 4MB with the expansion card. I seem to remember reading about people swapping or piggybacking RAM chips to upgrade earlier compact Macs where RAM was sorely lacking.
No, it'll be DIY made from scratch at home first. The ultra processed crap in a blue box with the letters KRAFT on it don't have enough resources to be able to do this
