jmtd → log → amiga → Amiga floppy recovery project, part 3: preliminaries

This is the third part in a series of blog posts, following Amiga floppy recovery project, part 2. The next part is Amiga/Gotek boot test. The whole series is available here: Amiga.

The first step for my Amiga project was to recover the hardware from my loft and check it all worked.

When we originally bought the A500 (in, I think, 1991) we bought a RAM expansion at the same time. The base model had a whole 512KiB of RAM, but it was common for people to buy a RAM expander that doubled the amount of memory to a whopping 1 MiB. The official RAM expander was the Amiga 501, which fit into a slot on the underside of the Amiga, behind a trapdoor.

The 501 also featured a real-time clock (RTC), which was powered by a backup NiCad battery soldered onto the circuit board. These batteries are notorious for leaking over a long enough time-frame, and our Amiga had been in a loft for at least 20 years. I had heard about this problem when I first dug the machine back out in 2015, and had a vague memory that I checked the board at the time and could find no sign of leakage, but reading around the subject more recently made me nervous, so I double-checked.

AMRAM-NC-issue 2 RAM expansion

Lo and behold, we don't have an official Commodore RAM expander: we were sold a third-party one, an "AMRAM-NC-issue 2". It contains the 512KiB RAM and a DIP switch, but no RTC or corresponding battery, so no leakage. The DIP switch was used to enable and disable the RAM expansion. Curiously it is currently flicked to "disable". I wonder if we ever actually had it switched on?

The follow-on Amiga models A500+ and A600 featured the RTC and battery directly on the machine's mainboard. I wonder if that has resulted in more of those units being irrevocably damaged from leaking batteries, compared to the A500. My neighbours had an A600, but they got rid of it at some point in the intervening decades. If I were looking to buy an Amiga model today, I'd be quite tempted by the A600, due to its low profile, lacking the numpad, and integrated composite video output and RF modulator.

Kickstart 1.3 (firmware) prompt

I wasn't sure whether I was going to have to rescue my old Philips CRT monitor from the loft. It would have been a struggle to find somewhere to house the Amiga and the monitor combined, as my desk at home is already a bit cramped. Our A500 was supplied with a Commodore A520 RF adapter which we never used in the machine's heyday. Over the Christmas break I tested it and it works, meaning I can use the A500 with my trusty 15" TFT TV (which has proven very useful for testing old equipment, far outlasting many monitors I've had since I bought it).

A520 RF modulator and external FDD

Finally I recovered my old Amiga external floppy disk drive. From what I recall this had very light usage in the past, so hopefully it still works, although I haven't yet verified it. I had partially disassembled this back in 2015, intending to re-purpose the drive into the Amiga. Now I have the Gotek, my plans have changed, so I carefully re-assembled it. Compared to enclosures I've used for PC equipment, it's built like a tank!

The next step is to remove the faulty internal floppy disk drive from the A500 and wire up the Gotek. I was thwarted from attempting this over the Christmas break. The Amiga enclosure's top part is screwed on with T9 Torx screws, and I lacked the right screwdriver part to remove it. I've now obtained the right screwdriver bit and can proceed.