Couple days ago I got the GF-5454 with unusual tuner problem. The tuner tracking seems all right, because the stations are found (kind-of) where I expect them, but when the station seems tuned, the audio signal is very low, and stereo works only when it is tuned slightly off the station, but with expected noise.
So, when the station is tuned, the output is like this:
Sharp_GF5454-tuner-signal-onstation1.jpg 85K 7 downloads
Now, in the middle of the scale, the strange noise is rather constant. Even the strongest stations have problems with it.
Sharp_GF5454-tuner-signal1.jpg 113.73K 2 downloads
Also, some strong stations seem to show in many places along the scale.
I am not an expert on tuner repairs, but this seems something like a problem with the mixer or first IF in tuner? The GF-5454 uses TA7335 for "FM front end" (IC1), AN7223 for FM/AM IF (IC2) and TA7343 for FM stereo (MPX, IC3). If I understand things correctly, this malfunction indicates problems with either IC1 or IC2, or perhaps 10.7MHz ceramic filter? Could it be that the oscillator in IC1 is slightly off and that gives IF not correctly on 10.7 MHz, making problems for other parts? Or is it CF bad, not filtering +/- 10.7Mhz correctly? Or is the IC2 bad, but just the FM section? I see IC3 as function normally, since the problems are same from mono/stereo setting.
All AM bands are working rather nicely. Quite sensitive tuner, I must say. Also, judging by the service manuals, the GF-5454 i very similar to GF-4646 (besides placement of knobs). I would like to upload the sm's, but the forum will not allow uploading.