An all in one stereo like the one you are having troubles with likely isn't worth repair if you look at things purely from a financial standpoint. If you know someone that might do the service on the side of you really care about not perpetuating the throw away society, these are the only reasons to consider service.
I have been 2 channel HiFi hobbyist since the late 70's and I did audio repair in the mid 80's for a time when I got out of electronics school.
"Affordable" HiFi components peaked in the US in the early 80's. By about 1985 many of the HiFi manufacturers were starting what I call the "MidFi slide". Basically we saw a parting of the waters where the companies that made decent gear in the late 70's to early 80's all slid down into the lower MidFi market. The true audiophile gear of that time started to slide yet further upscale, getting far higher priced and more limited in choices. This was a result of all the manufacturers trying to simply capture the most lucrative part of the market as people's tastes moved from quality into portability and convenience. Home theater multichannel audio and MP3's and portable audio would greatly increase the HiFi gap in the years that followed.
Indeed there is a lot of good vintage gear to be had on ebay, CL and local estate/garage sales. The only rub is that much of the 70's to 80's vintage equipment will require a bit of TLC due to age. Some components, mostly electrolytic capacitors will have aged to the point of being non-usable in some cases today. The various controls on the components have likely gone noisy from dirt, oxidation and non-use. All these problems are fairly easily put right but if it a DIY project one has to know which end of the soldering iron to hold etc.
I tend to be a fan of early 80's gear from Yamaha, Sony and NAD and some of the separate components from Hafler and Adcom are great deals today. I dabble in a lot of yet older vacuum tube audio too but this requires someone that is willing to do the work. Just like an old car they WILL require work.
The one part of vintage HiFi that I'm not a fan of is old speakers. Yes many of the old JBL and EV and Klispch speakers were very efficient and played LOUD, but age hasn't helped them. One can replace surrounds and spiders and even the cones themselves, but design of those days were pretty hit and miss. Modern speaker labs have much better instrumentation and design tools so todays speakers do sound better. But note that this only applies to ones that are high quality, most of the modern low cost stuff on the market is junk today, and I would take an old pair of AR-2's over that in a heartbeat! Note I say this owning a number of old Alnico magnet JBL's that are used a musical instrument speakers!
Bottom line is to figure out what your needs are and if the music makes you happy then you are set. Nobody else can tell you otherwise
