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Author Topic: Strange noise from R-4C  (Read 780 times)
VA3UT
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Posts: 14




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« on: October 08, 2018, 09:05:23 AM »

One of my R-4C has strange sporadic noise.  It happens normally after about 10~15 minutes of turn on but rarely after about 2 hours of operation.  Please check the video that I uploaded to youtube.

https://youtu.be/UQ8V5yDekWY

Can that be an issue with failing caps?  If so, which one?

Thanks.

Chris AD1AD & VA3UT
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AJ4SN
Member

Posts: 94




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« Reply #1 on: October 08, 2018, 12:23:33 PM »

I can't speak to the nature of the wind-like noise, but it sure sounds like you have a bad filter cap from the steady 60 Hz hum in the background. Maybe try that first and see if it is related to the wind-like noise.

Best of luck,

73

Stan
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VE3EFJ
Member

Posts: 97




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« Reply #2 on: October 18, 2018, 08:39:54 AM »

Fix the hum first. That is NOT normal. I'd first look at the 12V pass transistor. Did you notice that the noise you noted shows in the S Meter? Does the noise come from the audio chain or prior to the volume control? That is can it be adjusted with the volume control? I assume so.

Did you take any voltage readings? What is the serial number? Drake made a number of changes over the years in the 12V supply, especially the boost mod to get the 12V line to spec. That involved an electrolytic which *could* be your problem, but without any detail on the radio itself its almost impossible to advise further.
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WW3QB
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Posts: 816




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« Reply #3 on: October 21, 2018, 12:44:38 PM »

Check C168 and C162 on the DC power supply board for the hum. After that you can look into other noises.
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