Jump to content



Photo

Sharp GF-5454 tuner problem


  • This topic is locked This topic is locked
2 replies to this topic

#1 HRmeteohub

HRmeteohub
  • Members (SA)
  • 122 posts
  • LocationCroatia

Posted 12 November 2017 - 12:18 AM

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:

Attached File  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.

Attached File  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.



#2 Superduper

Superduper
  • Boomus Fidelis
  • 6,877 posts
  • LocationSomewhere over the rainbow, USA

Posted 12 November 2017 - 01:16 PM

It just sounds like tuner has drifted out of alignment. You already have the alignment instructions which are as close to step-by-step as you can get. Align as prescribed and you should be good.

#3 HRmeteohub

HRmeteohub
  • Members (SA)
  • 122 posts
  • LocationCroatia

Posted 10 May 2018 - 12:33 PM

Thank you Superduper for nice advice!

 

I just had to trim a core of T2 VF transformer, for about 1/2 of turn and everything works OK.

 

I could not find/get FM sweep generator, so I have started preparing to build one. Then I got stupid/brave and just tried my luck. First I marked position of T1 and T2, then tried turning in steps of 1/4 of turn to each side. Adjusting the core of T1 did little good, but T2 made all the difference. I sure would like to see "S" curve on my scope, as described in service manual, but that will have to wait for now.

 

This Sharp is such a nice device. There are about dozen of screws to remove on the back, open the tape door, and the front clicks off. On opening I have once or twice pulled the counter reset key with the front cover, but that is not a problem.

Inside on the left, speakers are connected with one connector to main board. PSU is neatly tucked in corner, tuner is separate board. Most parts are easily accessible and the board is of good quality. It takes just 4 screws more to remove from the back case, and they are easily visible or marked.

Although GF-5454 is made of plastic, build quality is very good. I like its brown color, and there are only couple scratches on the front. Thanx to Superduper, this was an easy fix, and it needs just a little bit more cleaning, testing and then it will be put it in good use. Sound is rather good for only 3W from LA 4192 amp. The LED VU meter is also a nice touch, despite fake doubling the number of LEDs by "splitting" each one LED to look like two.

 

This one was built in mid-1983.

Attached File  SharpGF-5454-front.jpg   87.07K   5 downloads

Attached File  SharpGF-5454-back.jpg   95.87K   1 downloads

Attached File  SharpGF-5454-left.jpg   38.27K   4 downloads

Attached File  SharpGF-5454-inside.jpg   130.77K   5 downloads

Attached File  SharpGF-5454-VUmeterStereoIndicator.jpg   39.76K   4 downloads