Hey everybody.I have an FM radio (Nakamichi NQ711B) on my car.And i face a trouble about fm band.When i use Bluetooth or usb function, there is not any faults.Only using FM is problematic.

-The problem is while i listen fm radio channels after a while, the unit boosts the volume to the highest point randomly.As long as i do not touch volume knob, it stays at the highest.Once i try to change the volume it turns to normal level.

-The unit has
PT2313L for 4-Channel Audio Process
SL4745-CO-GM for AM/FM tuner
АС1751АР1А344 as processor
YD7388 for audio amplifier (This is a clone of TDA7388 i think)

So, i am not sure where should i start to track the source of the problem.This is my first time i need to work on an audio device.So Can you help me please by giving some ideas?Thank you.

 

Is this a real volume potentiometer or is it an encoder wheel? An real volume control would have limited motion and would always have the same level in the same position. An encoder wheel would keep turning through a full circle, usually with some clicks you could feel as you turn it.

 

Is this a real volume potentiometer or is it an encoder wheel? An real volume control would have limited motion and would always have the same level in the same position. An encoder wheel would keep turning through a full circle, usually with some clicks you could feel as you turn it.

Yes it is an encoder wheel i think.İt turns step by step and i can hear clicking when i turn that and it turns forever, there is not a limited motion.I think you asked that because you think the fault might be caused by that right?But if that is that faulty part, would not it have caused the same problem when i use the unit in usb or bluetooth mode?As i mentioned before i face that fault when i use only in fm mode.

 

Then the problem is likely a software glitch in a microcontroller that handles the encoder wheel. I suspect the program is going awry, and accidentally setting the volume high. When it sees the input from the encoder, it updates the stored value and sets the volume correctly.

Probably not something you can fix.

 

did the radio worked properly in the past?

 

Sounds like whatever selects the FM function isn't initialising a microcontroller correctly. Is the selection via a button press, mechanical switch operation, or touch screen?

 

did the radio worked properly in the past?

No i have been facing this issue since i installed it.

Sounds like whatever selects the FM function isn't initialising a microcontroller correctly. Is the selection via a button press, mechanical switch operation, or touch screen?

As i understand from you wrote, it might be volume knob.Right?Because there is no issue when i try to select fm.The problem is about the volume level only

 

Because there is no issue when i try to select fm

There clearly is an issue if the initial FM volume setting is wrong.
How do you select FM?

 

There clearly is an issue if the initial FM volume setting is wrong.
How do you select FM?

There is a button which is used both for power on/off and source change.I use that to change modes among FM/Bluetooth/USB/Aux.

 

If that knob is for an encoder wheel then I agree with Bob (post #4), that the fault is likely a software glitch.

 

I sometimes drive a Ford bus that has a similar problem; when I turn up the volume, it immediately goes back to zero, unless I turn it far enough. Maybe it's dirt or corrosion in the encoder, and cleaning it would help. If it was my bus I'd just get a better factory radio from a wrecking yard, or install an aftermarket radio.