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Yamaha AX-500 treble and bass knobs does not work

K

kapuchahaha

New Member
In my Yamaha AX 500 amplifier, when I turn the bass or treble knob, nothing happens. I wonder if it's the fault of the potentiometers, but I think it may be the fault of the 'Tone Bypass' button. When I click the tone bypass button, nothing happens, there is no noise or any signal distortion. CD Direct, Loudness, Balance etc. they work. Is it most likely that the tone bypass switch is broken/dirty? If I want to clean it, do I have to desolder it from the PCB and can I use isopropanol instead of Deoxit? Thanks in advance for any help
 
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kapuchahaha said:
If I want to clean it, do I have to desolder it from the PCB and can I use isopropanol instead of Deoxit?
Click to expand...
To do it right. Yes. I used to use a Pentel drafting eraser to clean the contacts. Then give the contacts a light coat of D100 before reassembly. Now I use and ultrasonic cleaner. But still give it a light coat of D100 before reassembly.
 
Welcome to AK! Sounds like you checked to make sure Pure Direct mode or CD Direct Amp are not engaged. Also, I believe that engaging the Loudnesss control in either direction will initiate its own EQ curve that bypasses the tone controls--I'll have to check this to verify when I get a chance. Make sure that the jumpers on the Accessories Send/Receive are in good working order. You might be on the right track with the Tone Bypass switch. I doubt whether the problem is with the potentiometers. It's suspicious that neither are working.
 
I will try to clean the switch tone bypass soon with a contact cleaner and see if the treble and bass work. Do potentiometers always crackle when they are damaged/dirty? If so, I think that their damage can certainly be ruled out because there are no any bad sounds, simply adjusting the bass and treble knobs has no effect.
 
kapuchahaha said:
I will try to clean the switch tone bypass soon with a contact cleaner and see if the treble and bass work. Do potentiometers always crackle when they are damaged/dirty? If so, I think that their damage can certainly be ruled out because there are no any bad sounds, simply adjusting the bass and treble knobs has no effect.
Click to expand...
It's difficult but not impossible to physically damage pots thru normal use. The more common issue is the build up of dust, oxidation, and corrosion, especially if they don't get much use. Add in a little heat from the unit and the pot's wipers can become deformed or glued in place from oxidation. If they are physically broken, you probably won't hear scratching noises that dirty pots make.

Also, tone controls will have capacitors inline which can fail over time. The in/out switch for the tone bypass is where I would start. Deoxit. Turn it off and on a hundred times and see if it starts making contact Good luck!
 
kapuchahaha said:
In my Yamaha AX 500 amplifier, when I turn the bass or treble knob, nothing happens. I wonder if it's the fault of the potentiometers, but I think it may be the fault of the 'Tone Bypass' button. When I click the tone bypass button, nothing happens, there is no noise or any signal distortion. CD Direct, Loudness, Balance etc. they work. Is it most likely that the tone bypass switch is broken/dirty? If I want to clean it, do I have to desolder it from the PCB and can I use isopropanol instead of Deoxit? Thanks in advance for any help
Click to expand...
Is there a tone control defeat switch on that amp that could be possibly ON?
 
egellings said:
Is there a tone control defeat switch on that amp that could be possibly ON?
Click to expand...
There is a Tone Bypas switch. With several AX-500 and AX-700 that I have worked on this switch is the single most troublesome switch in the amps. OP contacted me by private chat and I answered that in the past I have removed, disassembled and cleaned the switch. Getting it back together correctly is a pain.

When removing the switch one has to be careful because Yamaha bends 2 of the leads 90° flat against the board and they are easy to break off when straightening them. This goes for the A-520 also.

In the future I will try what Avionic suggested and use an ultrasonic cleaner.

:beerchug:,
James
 
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