It started with an experimental 6502 computer on a breadboard working perfectly well on my desk but nowhere else in the room.
It turned out I had forgotten to connect the RAM and ROM ICs to VCC, with proper connections it worked everywhere, but why did it work in the first place?
Then I teached myself Verilog by coding a PAL composite output, which didn’t work until I mistakenly held my hand 5 cm above the breadboard...
While building my H5 I faced also a lot of unexplained issue (some linked to my soldering skills, ok) which would happens regularly for a few hours, then disappear without me doing any change.
Last week, I had this audio connection on a 600xl motherboard not producing any sound, so I gave up, unsoldered the wire, but when I removed it sound finally came out... from a jack not connected! The wire was 1cm from the jack, but I had sound..moving the wire closer or further would just turn off the sound!
This week it was problems with a gotek, troubleshooting write failures, just to have it working without any changes a few hours later...
So conclusion, my desk might be haunted...
But I think I finally found the ghost and killed it:
I was experimenting since last night with an Arduino and a RF433 receiver to decode the signal from my projector’s screen remote without success. There was so much noise in the signal that I couldn’t decode anything. Noise is pretty common on these kind of RF receiver, so I tried to analyze a bit more and used the scope. There was a lot of noise, but actually a very regular one, a very nice square wave at....50hz.
At some point, I forgot to plug the jumper to the RF receiver but the Arduino was still getting signal from just the jumper wire, enough voltage to go high at 50hz.
I started unplugging every device on my desk one by one and measuring each time, and when I reached the last, the 50hz signal finally disappeared.
A very simple Anker 6 USB port charger seems to be leaking radio wave all around the place and is now sitting in a drawer.
I tested my 6502 computer, and it doesn’t work at all when I unplug the ram and rom from VCC, my FPGA video circuit is running smoothly, and I expect to face a bit less issues overall.
Conclusion, be careful about the RF generated by poorly shielded equipments, it can really waste a lot of your time on unexplainable issues...
