National Panasonic 702 B AM/FM clock radio static when off - UK Vintage Radio Repair and Restoration Discussion Forum

correiadesa · 9th Feb 2020, 1:14 am

Hi.
I've just bought an old National Panasonic clock radio. It was not working at all. After a quick cleaning with contact cleaner spray (except for the flip clock) everything started functioning but with a strange issue. When i put the volume down you can hear a weak and permanent static white noise sound coming from the speaker. When you turn the radio off that noise continues. It seems that this a permanent noise in the background. When you tune it to a radio station with the volume up you cant hear but i think its there. Ive looked carefully inside but everything seems to be ok. Can anyone help me or give some clues to repair this?

Graham G3ZVT · 9th Feb 2020, 2:07 am

Hi correiadesa and welcome.

Have you got a cordless telephone close to the radio?

correiadesa · 9th Feb 2020, 4:49 am

Thank you Graham.
I've tried in diferent places and nothing changes. The static noise doesnt seem to be an external interference and is a very stable noise and not scrachy.

boxdoctor · 9th Feb 2020, 10:34 am

Hi correiadesa, are you certain the sound is coming from the speaker, and not from the clock mechanism? Just a thought, as the clock will continued to be powered when the radio is off. Tony.

correiadesa · 9th Feb 2020, 1:53 pm

Thank you Tony.
It's definitely coming from the speaker and its loud enough to ear it clearly trough a silent room. I wonder if it could be a faulty on off switch.
Best regards.

Hybrid tellies · 10th Feb 2020, 10:43 am

When the radio is turned on and with the volume control at minimum do you still hear the noise?

camtechman · 10th Feb 2020, 11:08 am

Correiadesa

What type of display does the clock have?

If it's LCD, that can produce the problem.

Herald1360 · 10th Feb 2020, 11:39 am

Chances are when the radio is "off" it isn't OFF. Just muted. The noise could just be residual hiss from noisy transistors/resistors etc. It's easier for the radio/alarm design if the alarm doesn't have to physically turn on the radio power, just unmute the sound.

Does it sound the same with the radio on and volume turned right down?

correiadesa · 10th Feb 2020, 1:43 pm

Thank you Simon.

Yes, when the radio is turned with the volume at minimum level you can ear the same background noise.
Best regards.

correiadesa · 10th Feb 2020, 1:48 pm

Thank you "camtechman".
This is a little1971 flip clock transistor radio.
Best regards.

correiadesa · 10th Feb 2020, 2:10 pm

Thank you Herald.
I hope that is not the case because in a silent room that sound get's too loud. You couldnt use it in a bedroom at night

That sound( no hum noise, just a "shhhh" sound) is present when the volume is down. If you turn off the sound continues.
Best regards.

correiadesa · 16th Feb 2020, 6:12 pm

I found out that if you unplug the radio from ac current for some hours, when you plug it again to ac current, there is no noise. After 20 or 30 minute the noise returns even with the radio in "off" position. I 've tried to see if any of components were warmer than normal but didnt find any. There is one 1uf capacitor that when you touch makes a loud "hum" noise but i dont know if thats normal.

9th Feb 2020, 1:14 am	#1
correiadesa Diode Join Date: Dec 2019 Location: Porto, Portugal. Posts: 8	National Panasonic 702 B AM/FM clock radio static when off Hi. I've just bought an old National Panasonic clock radio. It was not working at all. After a quick cleaning with contact cleaner spray (except for the flip clock) everything started functioning but with a strange issue. When i put the volume down you can hear a weak and permanent static white noise sound coming from the speaker. When you turn the radio off that noise continues. It seems that this a permanent noise in the background. When you tune it to a radio station with the volume up you cant hear but i think its there. Ive looked carefully inside but everything seems to be ok. Can anyone help me or give some clues to repair this?

9th Feb 2020, 2:07 am	#2
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,715	Re: National Panasonic 702 B AM/FM clock radio static when off Hi correiadesa and welcome. Have you got a cordless telephone close to the radio? __________________ -- Graham. G3ZVT

9th Feb 2020, 4:49 am	#3
correiadesa Diode Join Date: Dec 2019 Location: Porto, Portugal. Posts: 8	Re: National Panasonic 702 B AM/FM clock radio static when off Thank you Graham. I've tried in diferent places and nothing changes. The static noise doesnt seem to be an external interference and is a very stable noise and not scrachy.

9th Feb 2020, 10:34 am	#4
boxdoctor Rest in Peace Join Date: Sep 2010 Location: Ripley, Derbyshire, UK. Posts: 785	Re: National Panasonic 702 B AM/FM clock radio static when off Hi correiadesa, are you certain the sound is coming from the speaker, and not from the clock mechanism? Just a thought, as the clock will continued to be powered when the radio is off. Tony.

9th Feb 2020, 1:53 pm	#5
correiadesa Diode Join Date: Dec 2019 Location: Porto, Portugal. Posts: 8	Re: National Panasonic 702 B AM/FM clock radio static when off Thank you Tony. It's definitely coming from the speaker and its loud enough to ear it clearly trough a silent room. I wonder if it could be a faulty on off switch. Best regards.

10th Feb 2020, 10:43 am	#6
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: National Panasonic 702 B AM/FM clock radio static when off When the radio is turned on and with the volume control at minimum do you still hear the noise? __________________ Simon BVWS member

10th Feb 2020, 11:08 am	#7
camtechman Nonode Join Date: Jan 2008 Location: Milton Keynes, Bucks. UK. Posts: 2,552	Re: National Panasonic 702 B AM/FM clock radio static when off Correiadesa What type of display does the clock have? If it's LCD, that can produce the problem. __________________ When I die, please don't let my Wife sell my collection for the amount I told her I paid for it!

10th Feb 2020, 11:39 am	#8
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: National Panasonic 702 B AM/FM clock radio static when off Chances are when the radio is "off" it isn't OFF. Just muted. The noise could just be residual hiss from noisy transistors/resistors etc. It's easier for the radio/alarm design if the alarm doesn't have to physically turn on the radio power, just unmute the sound. Does it sound the same with the radio on and volume turned right down? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

10th Feb 2020, 1:43 pm	#9
correiadesa Diode Join Date: Dec 2019 Location: Porto, Portugal. Posts: 8	Re: National Panasonic 702 B AM/FM clock radio static when off Thank you Simon. Yes, when the radio is turned with the volume at minimum level you can ear the same background noise. Best regards.

10th Feb 2020, 1:48 pm	#10
correiadesa Diode Join Date: Dec 2019 Location: Porto, Portugal. Posts: 8	Re: National Panasonic 702 B AM/FM clock radio static when off Thank you "camtechman". This is a little1971 flip clock transistor radio. Best regards.

10th Feb 2020, 2:10 pm	#11
correiadesa Diode Join Date: Dec 2019 Location: Porto, Portugal. Posts: 8	Re: National Panasonic 702 B AM/FM clock radio static when off Thank you Herald. I hope that is not the case because in a silent room that sound get's too loud. You couldnt use it in a bedroom at night That sound( no hum noise, just a "shhhh" sound) is present when the volume is down. If you turn off the sound continues. Best regards.

16th Feb 2020, 6:12 pm	#12
correiadesa Diode Join Date: Dec 2019 Location: Porto, Portugal. Posts: 8	Re: National Panasonic 702 B AM/FM clock radio static when off I found out that if you unplug the radio from ac current for some hours, when you plug it again to ac current, there is no noise. After 20 or 30 minute the noise returns even with the radio in "off" position. I 've tried to see if any of components were warmer than normal but didnt find any. There is one 1uf capacitor that when you touch makes a loud "hum" noise but i dont know if thats normal.