Bear with me here as I have tried everything I can think of.
The left channel just crackles with faint music coming thru.
I have replaced the output transistors with ones that tested good on my scope (octopus sweep). Replaced the volume control. replaced ALL the 2SC871 transistors. In both the preamp section and the tone board. I can swap the amp boards back and forth and the problem stays with the left so its not those. I have replaced the electrolytic in the ripple board. and a few of the channel specfic film caps. things that were not unique to the left channel I didn't look at too closely. I get a beatuiful sine wave out of the hi low filter board. But the output transistor gates on the left are an ugly square wave but it stays with the left side if I swap amp boards. I have probably done something else that I am forgetting but this is is drving me nuts.
The left channel just crackles with faint music coming thru.
I have replaced the output transistors with ones that tested good on my scope (octopus sweep). Replaced the volume control. replaced ALL the 2SC871 transistors. In both the preamp section and the tone board. I can swap the amp boards back and forth and the problem stays with the left so its not those. I have replaced the electrolytic in the ripple board. and a few of the channel specfic film caps. things that were not unique to the left channel I didn't look at too closely. I get a beatuiful sine wave out of the hi low filter board. But the output transistor gates on the left are an ugly square wave but it stays with the left side if I swap amp boards. I have probably done something else that I am forgetting but this is is drving me nuts.
If you are getting a square wave at the base ( not gate as in FET ) of the left-hand BJT,s then you are overrunning the signal .
As MJF says what type of signal is at the power amplifier section input ?
As MJF says what type of signal is at the power amplifier section input ?
The problem you are describing, crackles and faint music, is usually dirty volume pots and or Balance pots. When you spray the pots with DeOxit you should turn the Potentiometers fully back and forth about 20 to 30 times. Clean the rest of the pots and switches while you are at it. Good Luck.
If you have a sine wave appeared at the filter board out, F-1186,
and you have try swapping the two power amp boards,
and problems remain...
It left the section from output stage to the speaker connectors to be examined.
check the output capacitor, resistors, cables, connectors for errors.
As one of our members advised
A good visual check is always good first.
Dry joints, unsoldered joints, bad connectors, (open or short).
dodgy pots, bad relay etc.
Bad zeners, bad transistors, old caps, .
and you have try swapping the two power amp boards,
and problems remain...
It left the section from output stage to the speaker connectors to be examined.
check the output capacitor, resistors, cables, connectors for errors.
As one of our members advised
A good visual check is always good first.
Dry joints, unsoldered joints, bad connectors, (open or short).
dodgy pots, bad relay etc.
Bad zeners, bad transistors, old caps, .
Sansui was kind of famous for dry joints.
Do a blanket reflow after checking components.
Clean boards with soapy water, rinse, that will remove years of accumulated junk, dry thoroughly.
Use alcohol to flush out dirt from mechanical parts if dirty.
Put contact cleaner after thorough blowing and drying in pots, switches, cable joints (ribbon or round cables may be on PCB connectors, those can corrode).
Work the pots and switches after spraying.
And then reflow each and every joint.
Then start from the power supply with a series bulb.
Mostly it will be a silly fault, bad solder, or resistor pulling signal to ground, making it low.
Overall Sansui used good components. Finding the fault on an old set needs patience and caution.
Have fun.
Do a blanket reflow after checking components.
Clean boards with soapy water, rinse, that will remove years of accumulated junk, dry thoroughly.
Use alcohol to flush out dirt from mechanical parts if dirty.
Put contact cleaner after thorough blowing and drying in pots, switches, cable joints (ribbon or round cables may be on PCB connectors, those can corrode).
Work the pots and switches after spraying.
And then reflow each and every joint.
Then start from the power supply with a series bulb.
Mostly it will be a silly fault, bad solder, or resistor pulling signal to ground, making it low.
Overall Sansui used good components. Finding the fault on an old set needs patience and caution.
Have fun.
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When did this problem with the left channel begin? You said that you replaced the volume control so a reflow of your soldering on the left pot channel may fix it? Same with the 2SC871 transistors you replaced, a visual check with a magnifying glass to check that no 2SC871 transistors were put in back to front and all soldering is Ok? Also, check to see that no pins have been popped from above breaking the solder joints on resistors, capacitors, transistors, etc...they break from moving an electro cap, resistor, etc... on the component side, look along the solder side edgewise to see any that have popped. By the way! What did you substitute the 2SC871s with?
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