COMX-35: Part 4 (Final mods & loading software)
13Finally I get around to loading some software. But I make you sit through me rambling about replacing capacitors for a while.
First, I fiddled a bit more. Ended up replacing all of the capacitors bar one (I didn't have a 0.33µF electrolytic handy). Full list of replaced capacitors below:
1 x 1µF 25V
2 x 10µF 16V
2 x 47µF 10V
1 x 220µF 16V
4 x 20pF (20 or 200)
2 x 120pF (121)
22 x 100nF (104), including one on keyboard
plus the 0.33µF 50V I didn't replace.
I removed one 47µF capacitor during the RF-to-composite video conversion, so I only replaced two instead of three.
Reading the technical manual it appears that the reason for the electrolytic on the LM386 is to reduce power line hum (50 or 60Hz).
Surprisingly it was still working. However I did notice some small wavering in the text displayed on the screen that I don't think was there earlier - not sure - there was a 120pF capacitor used to combine the chroma & luma outputs ... ?
Anyway, finally loaded some software. First I wrote a program and then saved it, capturing the audio on my Mac Mini (Server) using Audacity. To get it to re-load I had to increase the gain by +12dB.
To load some archived software (stored as .comx files) I used the Emma 02 emulator to generate a WAV file - result is a mono, 32bit float, 22.05kHz output. As it was it didn't load, so I similarly decreased the gain by 12dB ... and it was happy! The documentation for the COMIX-35 clone also has some hints about loading software.
I tried Happiehap 2 (kinda-like Pac Man) and Get Your Gadget ... digitised speech!
Next time ... starting on the COMIX-35 homebrew clone ... and maybe also getting one of the newer BASIC versions to work in the real COMX-35.
The emulator includes a lot of software so you don't need to go hunting around for it.
Emma 02 emulator for CDP1802 systems (BASIC ROMs & software):
https://emma02.hobby-site.com/
COMX-35 software archive:
https://archive.org/details/comx-35roms
COMIX-35 homebrew clone:
https://github.com/schlae/comix-35
And various home brew projects using the RCA 1802:
http://www.sunrise-ev.com/1802.htm
Discussion forum on the 1802 processor (and COMX-35):
https://groups.io/g/cosmacelf/topics
Assembly Programming on the 1802:
https://tomswan.com/pub/collections/
Data sheets for the CDP1870, etc.:
http://www.cosmacelf.com/publications/data-sheets/
#comx35 #comix35