Checks before applying power in a ZX spectrum computer

Those excellent video by
JoulesperCoulomb
https://m.youtube.com/watch?v=IzgCmldm2H4


If power in then supplied...


at Pleiades lab the trick used on equipment not used for some time, is on for milliseconds then off, then wait, then on for a bit more etc. This is done to give capacitors some time to reform.