FM Tuner Goes a-Wandering Once Tuned - Sanyo G 2002 Music Centre

[MyOhMy]

I've come across a Sanyo G 2002 Music Centre, nowhere near a top of the range model by any means, and it will not behave once tuned into an FM station

I've posted a video of the problem on Vimeo with this description of the problem:


Sanyo G 2002 Music Centre with faulty FM reception.

Once tuned into an FM broadcast station, the tuner gradually moves away from the station although the Tuning Indicator in the Tuner Window does not move unless turned manually. If two FM broadcast stations are close together, the radio will gradually re-tune from one station to another.

In the video the tuning moves away from the broadcast station so I then manually re-tune back to the station only for the tuner to move away from the broadcast station once more.

This is NOT an issue of or with FM signal reception strength or positioning of the radio/music centre, it is a fault with the radio mechanism and/or functionality.

I've spent 5+ hours turning the tuning knob back and forth to see if this would help to no avail, I've twice relocated the music centre within the house with no difference to the problem and I've allowed the music centre time to adjust to my home temperature/environment and this also had no effect.


On a broadcast station that covers a wider part of the bandwidth, the same problem occurs but takes proportionally longer to manifest itself.

Is this a walk-away-as-it's-too-much-hassle-for-a-low-end-item or could this potentially be an easy(ish) fix? Other wave bands do not appear to be affected.

 

[baddboybill]

Tuners are a very difficult part to repair or adjust without the right equipment. Better off taking it to someone with the knowledge and equipment.

 

[MyOhMy]

Tuners are a very difficult part to repair or adjust without the right equipment. Better off taking it to someone with the knowledge and equipment.

Many thanks for the reply, I think I'll pass on this as it sounds beyond economical repair for a non grail piece if audio.

 

[Superduper]

Mom, the problem you are having is not a mechanical but rather, a circuit issue. You likely have a problem in the local oscillator of the tuner front end. Volumes have been written on the theory of operation regarding how this works so I'll not get into that here. Essentially, what is likely happening is that the oscillator is drifting and not stable. This is possibly a symptom of a semiconductor failing (transistor, etc). If you want to know more about it, you can google "local oscillator tuner" and "superheterodyne". Bottom line is that this is not a DIY repair for the average enthusiast.

 

[MyOhMy]

Mom, the problem you are having is not a mechanical but rather, a circuit issue. You likely have a problem in the local oscillator of the tuner front end. Volumes have been written on the theory of operation regarding how this works so I'll not get into that here. Essentially, what is likely happening is that the oscillator is drifting and not stable. This is possibly a symptom of a semiconductor failing (transistor, etc). If you want to know more about it, you can google "local oscillator tuner" and "superheterodyne". Bottom line is that this is not a DIY repair for the average enthusiast.

Gotcha, you're explanation is absolutely clear and I appreciate this. One thing that perplexes me, though, is how you come to know so much about (seemingly) all things audio, you really are a walking audio encyclopaedia!

 

[Superduper]

If you study anything long enough, and with enough interest, you'll come to understand it, or more of "it" at least. Unfortunately, radio tuner theory is not an easy concept to grasp compared to more simple electronic circuits such as audio circuits. Additionally, a lot of expensive instruments are required to service tuners which aren't necessary for much of audio circuit servicing. Sure, an oscilloscope or signal injector/tracers can come in handy in audio circuit servicing if you know how to use them, but I've fixed countless audio circuits with nothing more than a digital multimeter. However, when it comes to tuners, you may need AM/FM stereo signal generators, sweep generators, oscilloscope, frequency counters, marker generators, RF probes for some circuits, etc, etc. Not every service requires those and on some service, you can do it by "feel" or ear, but it isn't very accurate and while maybe OK for pocket radios or simple boomboxes, not really an ideal way to do complicated sensitive tuners. Even if you think you got it "fixed", it might not be performing to it's potential.

Here is a video I found that describes, in a simplified way, how a simple superheterodyne system works. It's about 3 minutes long so worth a quick look. Of course when the simple flow chart is replaced with electronic circuits, it will no longer look simple. In any event, the incoming radio signal is mixed with the signal from the local oscillator. Obviously, if the frequency outputted by the oscillator is unstable and drifts, you aren't going to be able to accurately track a station. Anyone interested in tuner servicing should view this (and other tutorials first) and see if you can grasp the concept. If you have difficulty with the simplified description below, I suggest you leave tuner service to somebody else, because the curve ramps up much steeper from there on and really, life is too short to devote the time and equipment to go that path.

https://www.youtube.com/watch?v=x9hnbzF9XC8

 

[Ghettoboom767]

Thanks for this Norm,very informative.😎📻🎼🎶

 

[MyOhMy]

Thank you once more for taking the time to further explain the nature of the problem and provide a video for clarity. Most of it made complete sense although I doubt I could repeat it with absolute clarity after a decent sleep but, more specifically, this part nailed it in a few words with the support of the more lengthy description:

In any event, the incoming radio signal is mixed with the signal from the local oscillator. Obviously, if the frequency
outputted by the oscillator is unstable and drifts, you aren't going to be able to accurately track a station.

You're a Star, Sir.