Just an FYI on powering up or repairing older audio gear. Of the 50+ capacitors I just replaced in a vintage 1979-80 era Sansui integrated amp, they were all sill within capacitance specs except a few of the very small 1uf caps, all the larger caps (25-470uf) in the power supply & signal path sections tested within spec. The smaller ones that were off a little still allowed the unit to function ok and didnt trip the protection relay which indicated they were still functional. Other specs for caps like ESR & V-loss were within acceptable range but slightly higher than the new caps. Point is, good quality older caps will usually function ok but are at the end of their life and should be replaced, for speaker crossovers or electrical gear.
Electrolytic caps will almost always show signs of swelling, expanding or leaking fluid before a catastrophic failure. Pull the cover and visually inspect the caps & boards for signs of leaking or swelling or other signs of overheating from resistors etc before powering up. If it worked Ok before being stored away with no problems, it will most likely power up & work ok now... but again it always a good idea to have some type of protection, whether thats on board fuses or an external one in the power line or a device like a dim bulb tester shown above that is specifically for protecting things like this that may be in unknown condition.
Before the recap on the sansui when I was repairing a bad left channel, I asked about replacing the caps first, every experienced tech I asked said the same thing about caps, that they were most likely not the cause or reason for the problem and its always best to find the problem before just replacing things that probably are not bad, kind of the same approach for cars, always best to diagnose & find the actual problem first before just guessing & throwing parts at it.
Sorry for the long boring posts on capacitors... stereos & related electronics are like cars & oil to me.
