Why not use flux remover for removing flux, the clue is in the name 😉 WD40 is definitely a bad choice for electronics, its a mix of many hydrocarbons including waxes designed for repelling water from engines! It will make surfaces sticky and collect dust and grot that can eventually conduct... Meths can have all sorts of additives depending on the brand, again unwise choice. IPA is a relatively safe solvent commonly used for cleaning electronics though it might not be the best for fluxes its compatible with most electronics.
Rosin flux on old circuits can go dark with time (and heat), its not very chemically stable being full of unsaturated polyterpenes which can oxidize over time, or react in the presence of mild acids. But fluxes have a lot of different formulations, if you know which specific flux is involved you may be able to find recommended flux remover for it.
Rosin flux on old circuits can go dark with time (and heat), its not very chemically stable being full of unsaturated polyterpenes which can oxidize over time, or react in the presence of mild acids. But fluxes have a lot of different formulations, if you know which specific flux is involved you may be able to find recommended flux remover for it.
Your output relay is defective. You burned the contacts with your oscillaton experiments. If the problem occurs, tap the relay and it will go away for a while. This will show you the contacts are unreliabel.
I am a professional hand typesetter. The best way to clean flux residue is to dip your card in 99% alcohol produced for cleaning and wait until it dissolves. Then shorten the bristles of a paintbrush. Shortened bristles harden and brush well. Then hold compressed air. Repeat the same process one more time with new alcohol. Bingo is spotless.
There's an idea! 🙂
Chemtronics Flux-Off and MG Chemicals Flux Remover are excellent. Flux-Off comes with an ESD-safe cleaning brush that attaches to the can.
You can also help yourself by using aqueous flux, i.e., water-soluble flux. That can be removed with hot water (60 ºC).
Tom
Compressed air can generate static, I wouldn't risk it (and most don't have it!).