tu 9900 annoying tone

[andrew c.]

Good morning. Now that the weather is clearing up, I am refurbing a recent aquisition, a sansui au 9900 / tu 9900 pair. Almost everything works perfectly with one annoying exception. Amp is great. Tuner functions great. When tone calibration is engaged, all sound is cut except tone, and all lights, meters work. All good. with tone off, and muting off, there is typical static between stations. With muting on, the stations are clean and clear. Between stations, the calibration tone is heard as if it were on. I would expect silence. Am I doing something wrong, or is this "normal?" I have never owned this series before, and can find no info about the tone being on with it off.
A friend gave me this system. She was going to throw it in the trash as it was old and she had something new and small.
All the switches have been thoroughly cleaned, all caps replaced with "good" ones. Almost all the transistors replaced as well. I tried adjusting the pots. 601-604 don't seem to have any affect, and vr605 is the overall tone volume. Nothing has had any effect. That's the reason I undertook the tu9900 rework in the first place. I foolishly thought a leaky cap or transistor. Never so easy..
Any insight would be greatly appreciated.
Thank you in advance,
Andrew

 

[KeithD]

With muting on, the stations are clean and clear. Between stations, the calibration tone is heard as if it were on. I would expect silence. Am I doing something wrong, or is this "normal?"

This is not normal. With muting on, you should have silence between stereo stations like any other tuner. However, I'd don't have a suggestion for what might be wrong, sorry.

 

[Sansuiman]

That's a very odd symptom, not one I've encountered before. No immediate ideas on what to suggest. I will say that's a very nice pair to have saved from the landfill, it's good you caught it before it hit the trash. In proper condition, these are amongst Sansui's most sought after gear.

 

[Robisme]

Disclaimer: I am not a tuner guy.

Looking at the schematic, I recommend checking transistors TR614 and TR615 and all electrolytic caps around them.
Make sure all grounds are good.
Clean the calibration tone switch.
It looks like a section of the power switch is in the circuit as well. Maybe. Clean that.

Sounds like you have the test equipment to trace the tone and see why the circuit still tones when it shouldn't.

Rob

 

[andrew c.]

Thank you all for replying. I have been working on this on and off for two weeks. It's had me stumped. This morning, I was measuring everything I could, and found that when I fumbled a clamp on test pin 07 on board F2526, It all straightened out. Turns out, after replacing everything, The culprit was a cold joint on the base of test pin 07. A dot of solder, and it seems all is well. It's running now with no interstation tone, total silence.
I have been using a sansui 1000a as my main unit. I will have to give this one a shot.
Thanks again for the input, Andrew

 

[Sansuiman]

@andrew c., good find. Problems like cold joints can be a real pain to track down.