Sansui TU-9900 F-2528 Board

[Rotoflex4]

Hi all,

Found a modification on the F-2528 (Switch Circuit Board) of my TU-9900 Sansui. I don't know if this is a factory mod or a previous owner's handiwork. It's not documented in the service manual. Two traces have been cut, a jumper wire added and a 220ohm resistor installed. It is directly behind the Bandwidth pushbutton switch. I don't suppose anyone else has their lid off and can comment on what theirs looks like? (easily viewed from the top). Neither the Noise Canceller Switch nor the Low Pass Filter Switch seem to do anything when pressed (I mention this in case a modification has affected their functionality). Any insight? Thanks.

 

[Punker X]

I have one on the bench right now that does not have this. But it does look familiar, and would say it was a factory job.

If you are using a stereo RF generator and a sine wave you can see MPX artifacts on the sign wave with out the low pass filter engaged. They will disappear when switched in. The noise canceler is dependent on how the tuner is aligned. At higher signal level it will not do any thing. As signal deceases it will decease separation. I often see this misaligned and working at all.

 

[Rotoflex4]

I have one on the bench right now that does not have this. But it does look familiar, and would say it was a factory job.

If you are using a stereo RF generator and a sine wave you can see MPX artifacts on the sign wave with out the low pass filter engaged. They will disappear when switched in. The noise canceler is dependent on how the tuner is aligned. At higher signal level it will not do any thing. As signal deceases it will decease separation. I often see this misaligned and working at all.

Thanks, Mike. That's very informative / helpful.

 

[rcs16]

sine wave
The noise canceler ckt is a variable stereo blend filter using a special opto-coupled variable resistor. The detected IF signal level controls the opto drive level.