Back in the late 80s and early 90s, when the Amiga was relevant as a technical revolution, I was never able to lay my hands on anything beyond an 68000 with 7.14MHz. Years later, around 1997, I acquired an Amiga 3000 with 25MHz as part of one of my university side gigs of porting software from various UNIXes (in this case SCO Unix) to Linux. But a 040 or even 060 was far out of reach until I was well into my first full time job at SUSE Linux when I got a Cyberstorm MK1 that – as we know – doesn’t fit into the A3000. Long story short, the first time I actually ever ran an Amiga with something faster than the 68030 @ 25 was around …. Christmas 2019.
As life happens, and we sometimes overcompensate for our youth’s desires as we grow older, I added one of Chucky’s A3660 rev 1.1 to my collection, (built by Nicolas Baumgardt who lives in Switzerland, but only few miles from where I grew up and hacked on the Amiga back in 1987) that so far consisted of the A3640 that screamed for pad replacements and recaps.
Along the way I learned that the Amiga CPU local bus is really a 68030 bus, so memory access on everything above a 030 has to be translated and is then slightly slower than with an actual 68030. Ouch.
I also learned that the Zorro III slot is not really all that great. Well, Super Buster is not in its current implementation. While the theoretical maximum of Zorro III beats the first PCI standard, the actual implementation is stuck at 8-10MB/s memory access speed. We need an update Dave Haynie! Then our BigRAM+es could be really super awesome!
But back to … back to the 68060. Once I tasted the sweet excess of the Motorola flagship’s raw CPU power, and when I got my beautiful Hakko soldering station, I had to upgrade my 3640 to a 060 processor as well.
To do that, you need an adapter that converts from one CPU pinout to the other (similar to the overdrive CPUs in the 90s)
And here comes the journey. I did make the mistake (a beautiful purple mistake) of ordering three PCBs for the a1k.org 68040 to 68060 adapter from OSHpark for USD43. As I found out later, PCBway would only charge me USD5 for 10 PCBs.
The assembly is a game of patience. Because I had the PCBs produced with the standard width of 1.6mm it was unfeasible to solder on 68040 or 68060 sockets onto them. So off to Ebay to grab pin headers and extract the pins from them, as there does not seem to be a place that sells pins at a reasonable price.
The whole concoction consists of two boards, the 68040 part and the 68060 part. The top part converts the current from 5V to 3V. Since most pins are identical on both processors, they are directly passed through between the two boards. Not all of them, however, and these pins will have to be cut on the top board. The PCB I used had little circles around the pins that needed cutting, to make the process almost fool-proof.
To keep the pins from falling out, or from slightly shifting when soldering, I used a 68040/060 socket on top to hold them in place. I also soldered one line of pins at a time, and cut the pins right after finishing each line, as this would get to be a nightmare, as XXXXXX (name redacted) a dear friend of mine had to find out shortly before dumping his version of the adapter into the trash 🙂
Now I always prefer SMD components to through hole stuff, but in this case the through hole portion is mind bendingly annoying. Mind you, it requires soldering about 400 pins in a very tight space. It is very easy to either use too much or too little solder, keeping the pins wiggling or put solder on the tip of the pins, which will need annoying reworks later as the whole thing is a tight, tight fit. Nothing that can’t be solved with overzealous flux use.
Last, bring out the toothbrush and the flux remover, and give both parts a good rub, and it’s time for a test.
Yippie! It works.
As I had another PCB and the project seemed easy enough, I sold the first version on Ebay after several hours of testing and started working on the second one. This one is completely assembled, but after all this time still not working. The story continues….
I also got another batch of sockets and PCBs… This time I made the PCBs 0.8mm thick (half the normal size), so I can just use normal PGA sockets instead of going down the pin craziness again.
But even now, things are not as easy as I had hoped. Turns out, my sockets have 5 rows of substrate, of which the 68040 uses 3 and the 68060 uses 4. Unfortunately the PCB design places some components right under the inner substrate and the 10uF caps I am using are just a tad too high.
No problem! That’s what dremels are for.
My fellow Amigan Adam Polkosnik suggested to use an intermediate socket to avoid cutting the pins all together. That makes for a nice and clean solution and cuts some build time off the adapter too. Very elegant and clever.
And along the way I ran out of diodes to build the next adapter. I hope that having a third adapter will allow me to debug which of the two halves of my second adapter is buggy.
To be continued…