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An old stereo/radio system that hooks up to speaker system for surround system

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It has a weird buzz like a blown speaker but it isn't the speakers

The mixer is broken and a couple other items but that's not my issue..... my issue is as of now an hour ago i turned it on and it started buzzing and i know it's not my speakers because i switched them out for new ones to make sure and the same name came through. It is 40 yrs. old but it hasn’t had any major issues through it’s lifetime. Help!

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It fluctuates with the song currently playing but if i can i will post a audio recording it started this morning after i turned it off for an hour

and i hooked it into an outlet by itself

for example if i'm playing Highway to !&&* by AC/DC the bass works but I can't hear the lyrics and if i can they're very very light like a radio station you get a bad reception for

Following the principal of firstly checking the easily diagnosed and easily fixed things, take the covers off and look for bad electrolytic capacitors. See https://wiki.restarters.net/Basic_electr...

I've looked at it closely and looked for bulging or sideways capacitors and they all look reletivley new keep in mind this one is 40 yrs. old so there is a bit of dust and rust but everything mostly works

I did find a rusty fuse with a deformity but it isn't burned through

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Is this a mains frequency buzz? If so, I'd suspect a bad electrolytic capacitor in the power supply. If not, perhaps you could make a recording and post it. Is it a constant frequency, loudness and timbre?

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It sounds a bit like a problem I had with a large sound mixer a couple of months ago. At some (low) volume levels the monitor output was distorted, probably clipped. It turned out to be a CMOS analogue switch (type CD4066 I think, or similar) used instead of a multipole mechanical switch to switch the signal path. Someone had removed it and bent one of the pins in reinserting it in its socket, resulting in it not being properly biased.

The preamp stages probably are supplied by both positive and negative rails allowing the signal to rest at 0V when quiet. Possibly one of the rails was failing causing asymetrical power, and if the unit is now completely dead, perhaps that rail has now died completely.

Firstly, check the positive and negative rails, and if they seem ok then identify the ICs, most of which may be operational amplifiers such as TL084 or the older LM741. Find the datasheet online and hence identify which pins are the positive and negative supply. Check the voltages.

In the end, it's still quite likely to be a bad electrolytic capacitor - if it looks good that's no guarantee that it is. The component analyser pictured in the Restarters Wiki article will tell you definitely, or you can just change all the larger ones anyway.

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