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Very loud popping on 1 channel

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dica_455

New Member
Hi guys

I'm trying to restore my father's old Sony STR 6045. The left channel sounds OK (but a little underpowered). The right channel produces very loud static and popping, with a low hum. This happens with the volume all the way down. I've tried to deoxit but made no difference. I suspect bad transistor(s), but not sure where to start. Would the amplifier board make sense? And without unsoldering the transistors, would I be able to test these with a multimeter. Any suggestions on where to start would be greatly appreciated.

Tks
 
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dica_455 said:
OK. Tks for that. Those are transistors?
Click to expand...
They are. At this point in time there are some known transistors that degrade/corrode and no longer function properly. Really common problem nowadays on a lot of gear, but a relatively easy fix if that's the problem. Marantz receivers have some nasty transistors on the tone board as well that often need replacing, don't know about your Sony.
 
In your case I would say that since you are hearing this noise with the volume all the way down and there is a hum as well this indicates you have blown out put transistors on that channel. The hummus caused by the shorted output transistors basically placing the power supply voltage right on the speaker. Do not try and listen to this thing on speakers until it has been repaired. Look on the internet and read about how to test transistors. You will need a multimeter with a diode range.
 
With the volume down, the pops, would, should be in the power amp section.
A output transistor being bad there should trip circuit protection.
I would suspect a small transistor.
A telltale sign is black tarnish climbing up the legs of the transistor and making it's way into the die.
Bad output transistors for me have caused a total failure of the channel or extremely muted, muddy, distorted sound from that channel. Pops have been caused by small predriver etc. , tarnished, or just failed transistors.
Either way they should be removed for testing.
Removing them is very quick once access to the board is obtained. And then I would just replace with a modern substitute.
Myself I also have to do both channels.
To me it's like changing 1 windshield wiper or waring 2 different shoes
 
Agree with the issue being in the output section. This receiver has no protection circuit, but it does have fuses on the outputs, shown on the schematic right before the speaker selector switch. And there's a possibility that if one of those fuses blew on the bad channel, a previous owner may have installed a larger fuse to prevent it from blowing.

Whether that's the case or not, it's always a good idea to check fuses in used vintage gear for just this reason.
 
Tks Jimbo40. I appreciate the feedback. Looking to find modern transistor replacements now. I'll update when I get further with this little project...
 
Good luck, I do believe you'll find the problem there. I've had a few receivers where they'd switch between low random static to full-throttle noise even with the volume set to nil. Problematic transistors every time.
I'm about to change out a few I missed in a larger Marantz unit; I can hear low-level static randomly so it's only a matter of time now. Cheers.
 
Thread is few months old, but I restored one of these back in febuary of this year and it had the same problems. As people have pointed out the transistors in the tone board were causing the popping and crackling. I forget the exact replacements but shouldnt be hard to find on here. Also had the hum(not very loud but noticable) which took me forever to track down but it was a 8.4v diode in the power supply board (D801 I think) which i replaced with a 8.2v diode which works fine. Also recapped everything and replaced a few out of spec resistors. Hope this helps, you might have different components failing possibly though.
 
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