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Sony str-6055 enigma

Chriswashere

Chriswashere

Active Member
Well, instead of finishing projects to the very end, I've been jumping to some old ones that never would reveal their problems.

Of all the units here, this Sony str-6055 is the one that has caused the most interesting problems. Upon getting it 4 years ago, it was dead. According to my notes the diode bridge was blown, and the fuse for the power supply was removed. After replacing the diode bridge with an equivalent (Rs205), replacing all the power supply caps, and inspecting all parts on that board, the unit actually worked. For a few days I slowly kept creeping up the voltage on the Variac. Every few days the voltage would get raised, and the unit would sound better and better. Then at 70 vAC it died, giving off a horrid hum and blowing the fuse. After that, it has never recovered. I replaced the caps again (those little green 0.022 ones), inspected all parts, etc. And nothing.

So, a few moments ago I threw it onto the variac after sitting dormant for a few years, and got some very interesting results. My Variac is only putting out 5.0 VAC. That's it! At 5 VAC this unit is humming extremely loud and the diode bridge (Rs 205, formally 5b4 or something), heated up enough to cause burns if someone dared to touch it.

Any ideas? I just like messing with the stuff and am far from the professional level. It's just a hobby that I have very limited time for. Any help would be great.
 
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You may have a couple of things going on here. The unit may be humming and protesting because there is still something wrong with it, regardless of the voltage you are giving it.

Even if the unit was fully functional, it may not like getting voltage this low, and you would probably still get some strange noises etc going on.

Have you pulled and tested the outputs?
 
I can agree that something is wrong with it. It just should not be sending that loud of a hum through the speakers. When the voltage is raised, the humming increases and then smoke comes off the power supply if I recall correctly.

According to my notes, the outputs were all pulled and tested good.
 
Of course never trust old notes. The top left output ended up being bad, but could that be causing all these issues?
 
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