SX-1050 tuner problem

Stevescivic

Active Member
Hey folks,

This morning I was setting up some LPs to have a listening session when I noticed that when I turned on my receiver that I could hear a reed relay clicking back and forth like crazy on my tuner board. I know it is a reed relay b/c that's the only type that would make such a distinct sound akin to a fluorescent lamp that can't "light" properly.

This is when the tuner is tuned into a specific station with good signal strength and the tuning needle is centred and the stereo light is illuminated.

I only hear the reed relay clicking back and forth when in in aux mode. The moment I flip to FM mode then the clicking stops. If I tune away from the station that was tuned to then the clicking stops. It is almost as if the relay is for the PLL quartz lock or something. It seems like this problem occurs on random FM stations with decent signal. I went as far as swapping my antenna with. a larger one so I could pick up more stations and stations with signal levels of 2.5 or greater seem to have this reed relay clicking problem whenever I switch away from FM mode. Going to Phono 1/2, AM or Aux causes the clicking to start.

What on earth is causing this and is this a result of bad electrolytics on the tuner board? When I purchased the 1050 from a supposed collector he had it stored in a damp basement so the tuner chip legs and the adjoining ceramic capacitor legs did have some green corrosion on them which I promptly cleaned up with some IPA and a stiff brush. Legs weren't corroded through. At the time it was really concerning to me as I believe there is one unobtainium chip on the tuner no?

The receiver was recapped last year except for the tuner section and it was done properly. It has been working flawlessly and I use it almost daily. Voltages to the tuner board were the first thing to be measured when I figured it up on DBT and subsequently on line voltage after a recap.

Summary:
1. When tuned into a good FM channel (not all are like this, only a few stations) that if I flip to any mode other than FM that the chirping is crazy. During FM use it is dead silent.
2. When FM muting is turned off (button pressed in) that the chirping completely stops.
3. FM radio otherwise works perfectly albeit not as sensitive or clean as my similar year Sony STR-7800SD that is directly beside my SX-1050 using the same antenna.
4. I discovered my FM needle is off calibration and upon closer inspection the tuning drum is cracked! It does have the metal sleeve that is the set screw goes into so I know that it is at least reinforced. Now how to fix that crack in the drum... any tips?


The tuner doesn't appear to have any of the known bad transistors so I don't think it is that but the caps on them are the original ones and my understanding is that replacing them probably wouldn't be a bad idea and shouldn't affect the tuner alignment at all.

Thoughts?

Thanks,
 
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Here is my BOM for my SX-1050 tuner board recap. Figured that before I start screwing with VR1-3 like the above post that I ought to recap the tuner board to at least eliminate any powering issues that could be causing things to go all flaky on me.

I am not sure on the transistor replacement equivalent for the tuner. There are a bunch of 2SC945A-Q trannys on the board and I'm not sure if I should bother replacing them at all or if I do whether or not I should use the KSC1845FTA version or the
KSC2383YTA version.

Suggestions?

Thanks
 

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  • SX-1050 Tuner Feb 6, 2019 BOM.xlsx.zip
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replacement for the original 2sc945 is ksc945c, but the others you mention should work as well. Q5 should be a ksc1845f
Mute relay chirp (grounding the L/R signals) could be the relay itself or the control or the 24V supply, have to scope to see what is causing it. There should be no chirp if the FM muting is off.
Check the operation of the mute switch, it could be flaky causing this issue, scope mute-in(#9) and the collector of Q8
mute out is a DC level that is a result of FM antenna tuned in signal level, could look at that signal as well.
None of those pots have anything to do with FM muting, so do not fiddle with them and follow the adj procedure if you do.
I guess you could try to glue the crack in the drum or replace it.
 
Hey RCS16, I did check the muting switch and there is no chirping when FM muting is turned off. The switch I thought was flaky too but I highly doubt it as there is a clear evidence that the FM muting is working perfectly while in FM mode. It is only when you flip to alternate modes that the chirping commences. It is really weird and leads me to suspect that I either have a bad solder joint, or flaky power to the relay coil which is why I thought of the idea to recap the tuner board. Forgive my ignorance but when you say mute in #9 you are referring to probing at pin 9 on the board and then probing the center pin of Q8?

When you refer to mute out does that mean the muting is turned off (button pressed in) that I should see voltage when there is FM signal? I would’ve though that muting on and I get FM signal that I should see voltage at Q8 since it is what should disable the relay and allow signal out to the amplifier.
Regarding the transistors.... I didn’t know that there was a difference between a KSC1845F and a KSC1845FTA. Good thing you looked otherwise I may blow up my tuner. Perhaps it is best that I don’t replace the transistors and just do a recap? Do tuner transistors fail? My radio interestingly works perfectly although not nearly as good or precise as my vintage Sony receiver directly beside it.

Sorry for the noob questions,
Thanks
 
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