This is definitely a boundary issue. Tell her in a nice way that you're happy to fix whatever she's having a problem with after your show is over/after you've finished whatever you're doing/etc. She may feel that it's always urgent but that's probably not the case. People will take advantage of you for as long as you will let them, so the key is to set realistic healthy boundaries. You're not saying you won't ever help, but you're doing it at a time that is more convenient for you.

If it's a faulty cord that is the issue, remind her that she needs to replace the cord. So the convo would go something like: "come fix this!"
you: "mom, i've told you the cord is the issue. This will keep happening until you buy a new one. I will be happy to come look at it for you once this program is over."
mom: "No come look now."
you: "I'm watching this program right now but I will look at it as soon as it is over."
Just keep repeating yourself until she gets the message. People often don't like when we start to set boundaries because you're setting limits. It benefits her to impose upon you, so she might not take it well at first. Eventually she will get the message, you just have to stick with the boundary.

I hope this helps!

DD