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Old 02-13-2018, 10:01 AM
dieseljeep dieseljeep is offline
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Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by Jeffhs View Post
Greetings.

I have a Zenith H480W AM/FM/stereo FM clock radio which works very well on AM, but FM is extremely weak. I must turn the volume up to maximum to hear anything, and even then the sound is very weak, with a hum in the background. This radio was working well on both bands until I decided to clean the slide controls for volume and tone; as soon as I sprayed the slide pots and tried the set again, FM reception all but vanished. The built-in FM antenna (a coupler attached to the FM antenna terminal, through which the line cord passes) is connected.

What could I have done wrong? I can't believe a shot of contact cleaner (Radio Shack brand, long before RS left my area) could do this much damage. In addition to very weak FM reception, I also lost the dial lights and the stereo FM indicator (the latter now does not light up when the radio is tuned to a stereo FM station, and the dial lights quit at the same time). Did the contact cleaner short out something? I'm thinking the cleaner must have knocked a heck of a short across some common component--common, that is, to FM and stereo FM, destroying that component and all but silencing the radio on that band and mode. I would like to restore this radio to its original operating condition, as it was my first "good" AM-FM-stereo FM radio. Could the contact cleaner have caused an internal fuse (if there is one) to blow when I turned the radio on again, or just what on earth could have happened? Is there a fix for the problem, or did that contact cleaner destroy a transistor or an IC?

Note: I do not have a schematic or a service manual for this radio, and don't have test equipment (save for a digital multimeter) either. If I can repair the set without too much trouble, OK, but if the problem is caused by a failure of multiple components (as I am afraid it is), I will just leave the radio as it is and use it on AM only. As an aside, the power-reserve backup battery for the clock is long gone; that is, it is still installed in the chassis, but since the radio is well over 30 years old, the cell died some years ago, resulting in the clock resetting itself to 11:00 after a power outage.


Thanks much for any and all replies.
First thing, carefully remove that ni-cd battery. I've seen them leak and cause damage to the PC board and surrounding components. A connection might have been damaged and when the cover was removed it came loose.
IIRC, they were made in Korea by Goldstar.
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