9090DB lost FM signal

Skywatcher

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Has anybody ever experienced a 9090DB completely losing FM signal? The voltages seem to be fine on the F-2549 tuner board, and the F-2619 PS voltage is set at 12.5 (was at 13.55v). I was just listening to the radio and heard the signal begin to cut out. The signal meter was dropping, and the tune meter swayed back and forth. Then it just dropped out completely. The BCE voltages at TR01 thru 04 seem to be fine. I am beginning to suspect something in the front end gave out and would really like to avoid going there. But if I must, I'll dive into it.
 
Those Sansui's can be susceptable to static shock on the front end. I was once using a length of wire as a cheap antenna while working on either a 9090db or 8080db. I touched the copper wire while finishing up the unit, and lost FM almost totally. No signal strength at all, and with muting off, I could barley pick up even the strongest station. Turned out I popped the FM RF amp 3SK41.
 
Those Sansui's can be susceptable to static shock on the front end. I was once using a length of wire as a cheap antenna while working on either a 9090db or 8080db. I touched the copper wire while finishing up the unit, and lost FM almost totally. No signal strength at all, and with muting off, I could barley pick up even the strongest station. Turned out I popped the FM RF amp 3SK41.

That's what I was afraid of and these front ends aren't the easiest to access. Although I am sure the worst part for me will be re-threading the dial cord. Not as bad as the Sansui SIX though. I have a similar problem with mine and the front end is a nightmare to access. I haven't had the gumption to go after that one yet. ;) But it at least still picks up the stronger stations. The 9090db picks up absolutely nothing.
 
I am trying to recall some FM troubleshooting basics from way back when. I seem to remember that if you have only static hiss, and no signal when muting is off, across the band, its usually FM font end, most likely RF amp. If it is cold quiet, no signal, no static hiss it is usually FM IF, or Descriminator, or missing 13.5v where its needed.
If your problem is the latter, being totally quiet, I would check the point on the FM IF board where the 13v goes to and make sure dropping resistors are ok and that you don't have a leaky cap.
And I have had issues of really bad solder connection on the 13v PS board, as well as bad connection in the molex from the heat buildup over the years that kills AM and FM
 
I am trying to recall some FM troubleshooting basics from way back when. I seem to remember that if you have only static hiss, and no signal when muting is off, across the band, its usually FM font end, most likely RF amp. If it is cold quiet, no signal, no static hiss it is usually FM IF, or Descriminator, or missing 13.5v where its needed.
If your problem is the latter, being totally quiet, I would check the point on the FM IF board where the 13v goes to and make sure dropping resistors are ok and that you don't have a leaky cap.
And I have had issues of really bad solder connection on the 13v PS board, as well as bad connection in the molex from the heat buildup over the years that kills AM and FM

It still has the "hiss" so it sounds like it may be the RF amp, or at least something in the front end. I will go back over the solder joints again in case I missed something the first time. Power from the PS is fine and within spec. I rebuilt the RF power supply when I resurrected this unit. It was working fine for about 2 months after the rebuild and all electrolytics were replaced including the AM/FM board. Thanks Tom, I appreciate all the help I can get.
 
There are three IC's on tuner board. They are SIPs I've have them fail on several occasions you need a scope to trace the 10.7 MHz signal through them.
 
There are three IC's on tuner board. They are SIPs I've have them fail on several occasions you need a scope to trace the 10.7 MHz signal through them.

Thanks Jim. My brother has a scope over at his place so I can check the SIPS when I can. If any of them are indeed bad, are there replacements available? I always had this uneasy feeling about finding a bad IC somewhere with these old things. ;) I can live without the tuner and just hook up a separate tuner if need be.
 
To look at the IF oscillator properly you need a spectrum analyzer. Then you need am RF generator to inject a carrier wave and the capability of modulating a tone. Its all fairly logical, and some of the Sansui Tuner alignment instructions are a little wacky, and they expect you have a genscope, which nobody does, better ways of doing it now.....
Probably best way to track the audio through the IF stages is with a modulated carrier frequency, say with a 400hz or 1khz tone on it, then you can track it with your scope set to look at the audio frequency....
 
Here is an update. It was the 3SK41 that puked. Changed it out and am now listening to FM once again!
 
Thank you kevzep! It was "fun" lol! The worst part was getting the dial cord back on and aligning the pointer.
 
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