amp left channel not working

[Bartelsh]

i own a pretty old philips amplifier. it has served well for 30(!) years with hardly any trouble. but now when i turn it on and play music, the left channel will stop working after about 5 minutes. when i play music louder it will be shorter than 5 minutes and when i play music softer it will be longer than 5 minutes. i dont know what that indicates but maybe it is helpfull for you guys. this problem is solved by turning the amp off and on again but it is annoying to have to do that every couple of minutes.

I really like this amp, it is the masterpiece of my collection and i would hate to have to replace it. any suggestion would help!

[Bartelsh]

If you can open it take a look at capacitors... 30 years is a lot, degration may be the issue...

capacitors  look fine, wouldnt explain why it does work in the beginning

[Bartelsh]

any inflated? if those circuits work in negative logic degradated capacitors may provide more voltage and may take that as "0"

sounds logical, get it, but i dont see any inflated capacitors. maybe a capacitor is a little bit degraded? that would explain why it stops after 5 minutes

[Bartelsh]

yep, the problem is; how many capacitors are there? do you've a multimeter?

quite a lot, but not all are relevant because most are for the display etc. yes i do

[Bartelsh]

ok, put in to measure resistance, an check every capacitor (don't forget the polarity). a good capacitor will show low resistance and will increase to infinite if you keep measuring it. In a digital multimeter will show numbers for a moment and then open line

low resistance and infinite sounds like two opposites. can you explain? i checked a couple capacitors already and one of them was infinite, what does that mean? 

[Bartelsh]

well that's for analogic it'll go from low to infinite

in digital it it shows in the range of 10(tens)-100(hundreds) Kohm it's ok, if it shows 0 ohm or something over Mohm it may be broken

so 62 Kohm is ok. how can you know for sure if it is broken?