I bought a Goldstar 7020a on craigslist. before I bought it I plugged it in and connected one of the leads up to the test squarewave generator and everything seemed fine (the trace was very bright) but a few days later when I turned it on the trace was only bright for a few seconds after being powered on (
https://photos.app.goo.gl/uCln92dJtA1ySQxf2)
do you know what could be wrong with it?