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Odd FM light situation Pioneer SX 680

Yemm66

Yemm66

Active Member
Hello all. Strange problem I can't figure out. I just recapped my SX 680 and all went well. No issues. Well, one.
I have a mysterious situation with the FM light. On power up the light will sometimes come on and sometimes not. At first it would always be off and then light up after about a minute. I resoldered the caps and components around the area. Now the light is off on startup and if I tap the top of the unit, the light comes on. Without fail, every time I tap the top, light comes on. When on it's in stereo mode. When it goes out, in mono. Also the Stereo light never shuts off when switched to mono mode. I have checked the wires and lamps and have run out of ideas. Any help would be appreciated. Thanks!
 
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The stereo lights on my 780 and 650 stay on when switched to mono. Can't help with the other issue, sounds like an obvious lose connection but who knows.
 
Schanz said:
The stereo lights on my 780 and 650 stay on when switched to mono. Can't help with the other issue, sounds like an obvious lose connection but who knows.
Click to expand...
Thanks for the information on the mono light. I would assume it is a loose connection, but it has me stumped. Can't seem to find it. Hopefully soon. Keeping me up at night. LOL.
 
The Stereo/Mono switch is a connection between the left and right channels in the audio path. The Stereo light control signal comes from the tuner and indicates whether the received FM station can be 'de-multiplex' into a stereo signal or not. If it can the light will come on, and you will hear stereo from the station, if not you get mono. The Stereo/Mono switch has no effect on the Stereo light, but even if you are receiving a good FM stereo signal the switch will make it mono from the speakers.
However what you are describing sounds like a loose connection.
Not being a tuner guy, that is about the limit of what I can help with on your problem.
 
merlynski said:
The Stereo/Mono switch is a connection between the left and right channels in the audio path. The Stereo light control signal comes from the tuner and indicates whether the received FM station can be 'de-multiplex' into a stereo signal or not. If it can the light will come on, and you will hear stereo from the station, if not you get mono. The Stereo/Mono switch has no effect on the Stereo light, but even if you are receiving a good FM stereo signal the switch will make it mono from the speakers.
However what you are describing sounds like a loose connection.
Not being a tuner guy, that is about the limit of what I can help with on your problem.
Click to expand...
Thanks so much for the information. I will have to remove the front end again and see if I can chase it down. Just so tight in there and hard to see. Hopefully I can get lucky and find the problem quickly. I really appreciate your comment!
 
You might want to check the wire-wrap connection at Pin 69 on the main board. It might also be helpful to clean SW-4B (FM Mute/Mono-Stereo) since its input to the IF/DeMod IC might affect the function of the MPX IC and its stereo lamp driver - Maybe. It can't hurt to have a clean switch anyway.

Incidentally, did I buy a Chevy truck from you once? (Any relatives in Galesburg?)
 
Watthour said:
You might want to check the wire-wrap connection at Pin 69 on the main board.

Incidentally, did I buy a Chevy truck from you once? (Any relatives in Galesburg?)
Click to expand...
Hi. I will try and look at that pin. I have tried everything else. I have poked with a stick all night. Also, found the capacitor hiding behind the LED board. 220uf 6.3v axial. Changed it and no difference. So strange. The light just went out again after sitting at idle for about ten minutes. Tap and back on.
I am related to the folks in Galesburg somehow. I am in the business as well. My father used to be part owner of the local Nissan/Datsun/Renault franchise back in the 70s. I am in sales at my local dealer here in town. I really appreciate your help with the suggestion and will give that a whirl. Hopefully I can post back and the issue is gone.....we will see. Stay tuned.
 
Stay tuned? Yeah, I see what you did there...

The input to Pin 8 of the PA1001 IC from Pin 12 on the PA1003 IC could have an effect upon the stereo lamp driver. I don't have an SX-680 here to check that function, just a pile of SX-780s which are similar but slightly different. That was the reason for the clean switch suggestion.
 
Watthour said:
Stay tuned? Yeah, I see what you did there...

The input to Pin 8 of the PA1001 IC from Pin 12 on the PA1003 IC could have an effect upon the stereo lamp driver. I don't have an SX-680 here to check that function, just a pile of SX-780s which are similar but slightly different. That was the reason for the clean switch suggestion.
Click to expand...
Checked pin 69 and pushed the wire at the base. Looks ok. Cleaned it up a bit more. Have cleaned the heck out of all the switches too. I have checked for any solder balls and other debris. Nothing I can see. I will run her again tomorrow and see what happens. I WILL beat this thing. LOL. Thanks again for your suggestions. Much appreciated.
 
May have found the problem. Up towards the front end under the tuning wheel, I started moving wires and the stereo light flickered and went out, then came back on again. Tried a few times more and the same result. The black and yellow braided wire seemed to be the cause so I followed it to the wire wrap and pushed it down firmly. So far, seems to be working. Fingers crossed. 522E8ADC-98A8-4B02-9141-2848C21DC536.jpegA9D26E9C-F4B9-4EEA-AA95-E2018BB8170B.jpeg
 
Back to the drawing board. intermittent again. It's in that corner somewhere. Every now and then I tug on a wire or group and it will go out. I'll keep trying.
 
Thanks to Merlynski, Schanz, and Watthour for your suggestions on the SX-680. I finally found the problem. The FM, Aux, phono selector turned out to be cold solder joint(s) on the pins to the board. I was bracing my finger against it while poking around and the light would go out with pressure on the metal box. I touched up all the joints with fresh solder and Everything is working great now. 8B37B820-B22A-4CA1-84BE-97B77373BD5A.jpeg
 
Easier than fixing the Electrical system on a Citroen. Gotta use the extra chunky French replacement smoke(particles larger than swiss cheese holes!) Lucas smoke leaks out too easily!
 
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