*this instructable takes for granted that you can solder, understand basic electronics, and have fixed electronic gear before.*
so you acquired an old stereo receiver but it has issues. there are many things that can go wrong with an old stereo receiver but one of the common issues can be blown outputs. sometimes the cost of parts is prohibitive, making it not worth the effort of trying to fix a piece back to its original design.
what to do? junk it? NO..
this instructable is intended to be an option for those that have a piece not worth fixing. vintage stereo gear can be valuable, even broken so don't just dive in till you know what you have. you may regret your actions later if by chance you had something quite valuable, even if broken. finally, this instructable is focused on transistorized stereo gear from the 70's and 80's. old tube gear is a totally different animal and not covered here. throughout this instructable an effort will be made at trying to solve some of the common ailments of old stereo gear. there's always a chance you might get lucky and what ails your unit is covered here and you are able to fix it instead of mod it.
with that out of the way, let's see what's up with this old marantz.
Step 1: a little diagnoses
time to hook it up and see what happens.
first thing, inspect the power cord. any signs of damage to the cord where you may be exposed to bare wire are a bad thing and need to be addressed before applying power. if cord is all good let's move on to powering it up.
what can happen? smoke, fire, sparks, or nothing at all. find somewhere safe to work in case something goes VERY wrong with your stereo. turn the volume knob down all the way, plug the power cord in, hit the power switch and watch.
smoke = bad
sparks = bad
fire = very bad
does nothing = not so bad
powered up and seems to be acting normal = doing good
if you got smoke, fire, or sparks, we are done here and that is beyond the scope of this instructable. your unit may have a catastrophic failure but may still be valuable to someone for parts. don't just trash it. put it up on craigs or something and let somebody else take a crack at it if it's beyond your abilities.
before we proceed keep in mind there are dangerous voltages inside old stereo gear. you can die if you touch the wrong thing inside an old stereo while its plugged in. if you are unfamiliar with proper safety procedures, you should seek the help of someone who is trained in working with high voltages.