Electricity and Electronics Courses

I'm a 68 year old with a B.Sc in Pure Mathematics and have used and donated to your excellent website.

I collect and (try to) repair vintage calculators, particularly HP & TI programmable ones. My current project is reviving a 1979 HP-97 calculator/computer which was the first machine I programmed with Business Applications. I've spent 35 years in IT but I now realise I'm lacking electrical and electronic skills to try and trace or repair faults or power on issues.

So I want to start studying Electrical and Electronics Courses so that I can trouble-shoot issues. There are a number of what look like suitable courses, but can anyone tell me the order of the courses I should take, bearing in mind I'm primarily a pure maths guy and my electrical engineering skills have not gone any further than A Level Physics taken in 1966.

I want to learn basic electricity and electronics so that I'm able to understand and write schematic diagrams and trouble-shoot vintage electronic faults in calculators.

All suggestions are welcome please.

Dennis Tuckerman