I decided to build a Minimig – a clone of Amiga, it can act as Amiga 500, 500+ or 600, with up to 4MB total RAM.
The interesting thing is that it uses an actual 68000 CPU – clocked at 7 or 50MHz in Turbo mode.
Other proprietary Commodore chips are implemented in FPGA.
I also built an ARM controller board – which replaces the small PIC micro, serves as SD card interface and feeds the FPGA with initial bitstream.
I’ve also included 3 hardware mod’s – additional 2MB RAM (sitting on top of original chips), SD high speed interface and lastly – joint stereo/separate stereo switch.
This was my first time soldering such a fine pitch (and expensive) chip – wasn’t all that hard.
I finally got around and completed the USB IR Toy v3.0 I got from Dangerous Prototypes .
Took me a while, had to go over the BOM, then I realised that I looked at the 3.3v version’s BOM etc., but it’s done.
(I had to bend the UART pins because my pickit wouldn’t fit and I was lazy to look for header extension).
I was just watching an eevblog episode about VIA’s (research for my project), and I saw Dave using Saturn PCB Toolkit for various calculations.
Interestingly (and not surprisingly) the tool is only available for Windows, but I wanted it anyway, so I decided to give it a try under WINE.
It wouldn’t install, throwing a few errors, but then I did manage to install it on my Windows and copy the .exe file over to my mac,
and – voila, the thing works, it should also work on Linux…
First part here
3 days later, my mouser order arrived to Japan (this is super fast), I got the relays, desoldered the bad one (proper desoldering tool is very useful here).
(Right is new replaced, left is the old one for comparison, didn’t take it apart though).
Soldered the replacement and couple of screws later, I had the multimeter repaired, reassembled and ready to test.
(Don’t forget to note colors of the internal cables connected to the rear panel posts)
First I realised that once or twice another test had failed (500.2), and also 600.1 and 601.2 (which was definitely a change from original 600.1,600.2,601.1).
When the test process asks for 4-wire short I literally used a 4-wire kelvin clips shorted, and this seems to be the reason why error 500.1 came up, and likely the 600.x ones now were because I shorted HI to LOW instead of AMPS.
Now, for 4-wire short I used pomona banana leads (I think 12-ich ones) to get as close to a “real” Keithley 4-wire short brace (it’s literally a brace with 4 banana plugs that snaps right into the posts).
After the change of leads – all of the tests succeed. Voila, I repaired the multimeter (but I think I will someday make a a 4-wire short brace for reliable testing).