SX-737 tuner AWE-043 with noise in STEREO

[pa_200]

One of my SX-737 still makes a permanent static noise as soon as the stereo light comes on. The noise stops as soon as the Tuning needle leaves the center marking, or if I switch to MONO.
The board has already got to light blue Sanyos together with some other caps and 2SA726 replaced.

I compared it several time with the other SX-737 and SX-828. All tuned to the same station and used the same antenna.

Is there a slight chance for a rooky to try some kind of alignment, without all the special equipment?
I have a set of plastic Alignment tools and this FM Test Generator, but always willing to learn something new.
https://www.amazon.de/-/en/Stereo-T...r_1_1?keywords=elv+sup3&qid=1640506419&sr=8-1

 

[larryderouin]

Couple of things come to mind.
1.) Cleaning the grounds on the tuning gang shaft, and FM De-Emphasis. NON-RESIDUE (make absolutely sure it says this on the can!) contact or electronics cleaner to spray down the tuning gang while exercising the knob lock to lock. Let it dry off, and use a toothpick dipped in DeOxit D-5 to the leaf's that are riveted to the frame and contact the shaft(these are the grounds). DeOxit @ the connection at the shaft.

2.) Look for a switch coming off pin 16 and 17 of the tuner board (should be on the back panel) that says FM De-Emphasis(S14). The US Standard is 75uS while Europe is either 50uS or 25Us. If yours is adjustable, set to either 50 or 25, whichever outputs the least noise. If there is no switch, You can build the circuit with a DPTT switch and a few caps. FM Multiplex Stereo uses an AM carrier for the L & R channel info. What you're hearing is the AM artifacts, which will never go away but can be minimized greatly with the correct DeEmphasis and correct alignment of the RF/IF circuits AND the MPX Circuit (2 separate evolutions).

Generally, you would need a Generator that put's out 19mHz and 38mHz, in and amongst the usual stuff used for aligning a tuner, PLUS A SERIOUS knowledge and experience in FM Multiplex. Give serious consideration to sending it out.

 

[pa_200]

I have the switch and it was set to 50uS, but no big change with the 25uS position.

Larry could you mark the position in the picture where I should use the cleaner on the tuning gang shaft
What we have here for tuner cleaning is this stuff, is that good enough?

https://www.amazon.de/Teslanol®-T6-OSZILLIN-Kontakt-Tunerspray-400ml/dp/B001FSXMO2

 

[larryderouin]

Ok.
1.) FM De-Emphasis in Europe is 50uS.

2.) According to the spec's for the cleaner it has a lubricant that will change the capacitance of the air gap between the fins (knocking the tuning off). The stuff you want is NON-RESIDUE and must state so on the can. Not familiar what you have in germany, check with an electronics store that has an older guy that is the tech and ask. If you can't find anything else, use canned air that you clean keyboards with, BUT DO NOT turn the can upside down. Then do the grounds with DeOxit.

3.)The arrowed areas have a brass spring contact. Dip a toothpick in DeOxit and put it on the contact area of the spring clip with the rotating fin shaft.

4.) The fins in the rectangle look like they are not parallel and could be touching slightly or it could be the picture. Do a straight on visual check(looking straight on the edge of the fins for equal spacing between fins meshed and unmeshed) while rotating the knob slowly lock to lock. Make sure they DO NOT TOUCH.

 

[pa_200]

The plates are parallel and not toughing each other. Made some macro picture to recheck the small fins.
Used some dry canned air to clean the fins and it sounds like this did the trick. Have a good Stereo sound without any noise for now. Hope that will remain long enough.