2270 - Flickering stereo due to noise

[ocdecio]

That's a great idea; however I am looking at the output of P500 (after the discriminator J509) and it is VERY noisy (1kHz wave through a transmitter):

https://drive.google.com/file/d/1uD-rKWim7qVGvwOQM8sQdW9oCqGAfuid/view?usp=sharing

The output of H501 (pin 2) jumps too, not as frantically as this one though.

 

[Steven Tate]

Can you measure the voltage at the base of H306? The base going from .1V to .6V (strong station) starts a chain reaction that results in MPX state. Since you are going in and out of stereo, it would be helpful to know if that is because the base of H306 is not getting a solid .6V when on a strong signal.

 

[ocdecio]

Can you measure the voltage at the base of H306? The base going from .1V to .6V (strong station) starts a chain reaction that results in MPX state. Since you are going in and out of stereo, it would be helpful to know if that is because the base of H306 is not getting a solid .6V when on a strong signal.

I can do one better - here's a video of the voltage. Set to 0.5V per division.

https://drive.google.com/file/d/1IA6eOyNYLKi0lLgJICziR6LHuI_oV2bb/view?usp=sharing

When the voltage goes up, stereo lights up. It is very jumpy and follows the noise seen in the other video

(it may take a while for Google to process the video so it may need to be downloaded my apologies for that)

 

[Steven Tate]

Sure seems like something upstream is not passing a steady signal. You said the signal at pin 2 of H501 looked unsteady. Can you tell if the input at J501 is steady?

 

[rBuckner]

Hmm, both links give me this:

 

[Steven Tate]

Hmm, both links give me this:
View attachment 2675877

When I hit "Download", I got the video.

 

[ocdecio]

Hmm, both links give me this:

My apologies, Randy. Google Drive takes some time to process the videos.

 

[ocdecio]

Sure seems like something upstream is not passing a steady signal. You said the signal at pin 2 of H501 looked unsteady. Can you tell if the input at J501 is steady?

Yes, J501 (which is the same as the P200 outputs) is steady and shows a wave very similar to the one I get in a working unit.

 

[rBuckner]

When I hit "Download", I got the video.

You're right! I believed the lie!!

 

[Steven Tate]

Yes, J501 (which is the same as the P200 outputs) is steady and shows a wave very similar to the one I get in a working unit.

Kind of points to H501, like you mentioned earlier. Right?

 

[ocdecio]

Kind of points to H501, like you mentioned earlier. Right?

That's the current thought. It could well be that I replace the chip and nothing happens but it is very strange to have such a jumpy signal off of it. I replaced the coil from a parted out 2230 just for the heck of it, no changes.