Nakamichi PA-7 Stasis Hum

My dad was very much into his stereo, and put together a nice Nakamichi system with KEF 107 speakers. He passed away in 2001, and the stereo doesn't see much use anymore, but for Christmas, or whenever my mom wants to watch a movie on the big screen. Unfortunately, the PA-7 has developed a very loud and annoying hum, and the left channel "warning light" lights up as soon as the amp is powered up. My first thought was that amp was always more than those speakers could handle (couldn't turn the volume up more than half way without those warning lights starting to flash), so why not just replace it with a less expensive one? After reading a bit on what it takes to properly supply those speakers with power, I'm now leaning towards getting the PA-7 repaired, but I don't know a thing about it, really. Is it worth it to get the PA-7 repaired, or could the same money be better spent investing towards another power amp? Keep in mind I don't have a lot of cash, and expensive stereos aren't the most important thing to me or my mother. I understand that's not the case with you folks, and I respect that, I'm just asking for you to keep it in mind when offering suggestions to us.
Thanks for your time,
Thanks guys. I'd say $500 would be the upper end of what we'd be willing to spend. I've also contacted the store the system was bought at (30 years ago now), just to see what their take on it is.
Appreciate the insight.
Make sure you try a new pair of Interconnects between the Pre amp and Power amp first
Or just swap in the good right channel interconnect into the left ch and see if the hum noise is gone .
I'm checking into getting the amp repaired, in the meanwhile, what amps costing $500 or less could drive those KEF 107s?
Thanks again!