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Re: Potentiometer and output transistors
Try sony for the transistors, they use them too, but expect a handling and delivery charge from all suppliers these days. It sounds like a standard 330 ohm preset pot by your descriptions. There are more than a dozen varients to chose from. You will need to compare the lead setup and pitch to get the correct replacement. I use Farnell electronics to mix and match odd replacements. Good luck
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Your volume potentiometer is dirty and not tracking properly. Clean it by turning unit completely off and then turning the volume control from full clockwise position to full counterclockwise.-- Repeat this for about fifty times or so. The motion of the wiper should have cleaned off the pot surface and restore operation.
Possible that the analogue to digital converter is faulty, possible failure of the potentiometer and the motor drive.If the volume does increase with the remote then it is possible that the POT or the circuit to it is faulty. check this D/A converter.
The problem is that the potentiometer that the knob is connected to is dirty. This is a common problem with age, or quality of installed potentiometer. (potentiometer is the name of the component that the knob attaches to. It usually looks like a 1/2" long cylinder)
There are multiple solutions to this problem. The first is free & anyone can do. While the unit is off. Twist the knob back and forth quickly and rapidly numerous times. Roughly 10-15 times will do. This sometimes allows for the connections within the potentiometer to reconnect, and remove the crackle.
The second solution involves some handy work. The unit's case will have to be disassembled, and the potentiometer that the knob is attached to must be found. There is usually a relief hole somewhere on the housing. Within this relief hole one can spray contact cleaner. This cleans the contact within the potentiometer which is the cause of the crackle. Once the pot has been sprayed, rotate the knob like in step 1.
If steps 1 & 2 do not work, the potentiometer will need to be replaced. This work usually needs a professional. If you are handy with a soldering iron, it can be accomplished. Look for any particular part #'s on the crackly potentiometer, and then copy these into a online parts catalog. Mouser.com and Digikey.com are excellent resources for finding parts. Upon finding a replacement, it can be swapped out, and provide the user with a crackle free knob.
As always, make sure power to the unit is disconnected. If you are unsure of electronics, please use caution, as dangerous voltages may reside that can cause personal injury.
The knobs are usually connected to a potentiometer; basically a variable resistor circuit with a long shaft that the knob attaches to. The knob could be secured to the shaft with a plastic grommet, which can be stripped. It could be attached by a small screw on the knob, and tightening that would fix it. Or, it's possible that the potentiometer itself broke, and would need to be replaced.
If the "pot" is broken, a repair shop should be able to fix it for less than $50. If you're handy with tools, you can take the 7100A apart; hopefully read the specs from the potentiometer; and buy a new one. Replacing it shouldn't take more than a few screwdrivers, some pliers, and a soldering iron...
The potentiometer doesn't need to be replace, it has collected dust inside causing the intermittent operation. Buy a contact cleaner/conditioner to spray inside it and move the potentiometer clockwise and counter clockwise a few times until the dust inside it is gone. Check this link to find a contact/conditioner cleaner or you can try spraying rubbing alcohol but this could because alcohol doesn't not lubricants properties.
Let me know if you require further assistance.
If the receiver is a new one (a couple of years) I suggest you don't replace the balance potentiometer. It's a potentiometer with rare use so the inner carbon film can't be destroyed. I suggest you to open the case and use a contact cleaner spray (clear, without oil) and spray direct at the potentiometer. Turn it all the way from left to right many times. When it will come dry you will see the diference. As far as the suggestion for clear (without oil) contact cleaner spray, I insist on that because the lubricating oil will cause a trap for the dust and will ask for cleaning again and again. Also for potentiometers with rare use there is no need for lubricating oil.
I think that this solution is much easier than chanching a potentiometer, since the device is not too old.
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This sounds like a power supply problem. The high voltage for the tubes is not right. Either you are missing an amplification stage because this or one of the coupling caps is faulty. I'd have to see the unit itself to give you any more details.