Fixing a Buzzing Clock Radio

I’ve been using this clock radio for at least twenty-three years, and I love being able to read its huge 2″ digits when I wake up during the night and my eyes are blurry and unfocused. It’s having a little trouble here competing with the sunlight streaming in the side window, but it’s nice and bright at night when I need it.

Spartus clock radio

Lately it’s picked up an annoying habit of buzzing at, you guessed it, 60Hz. The intensity and timbre of the buzz vary, sometimes coming and going at the same time I can hear the furnace fan starting up and shutting down, sometimes apparently at random.

Listening carefully has led me to believe that the buzz isn’t coming from the speaker end of the clock, but rather from the power supply end. Speaker buzz would suggest bad filter capacitors (and one could certainly forgive twenty-five-year-old electrolytics for needing to be replaced); but power supply buzz makes me think of transformer windings coming loose and needing to be re-epoxied, metal brackets near the transformer working loose and needing to be tightened, and that sort of thing.

Today I had time to open it up and — I think — fix the problem.

Spartus clock radio, interior

Most of that is radio circuitry, and I don’t even use the radio. The clock part appears to be two ICs underneath the raised pushbutton circuit board. The transformer is in the “basement level” between the two posts to the left of the display’s ribbon cable.

Transformer with loose mounting screw

Right away I could see something I suspected was at least part of the problem. The transformer’s forward mounting tab was bent at other than the proper 90° angle from the body, only one edge of the mounting screw’s head was in contact with the tab, and there was a lot of slack between the tab and the mounting boss.

After removing the main PCB to make room to get a screwdriver in there and straightening the mounting tab with pliers, I got the screw tightened down properly. I could tell that the screw hadn’t worked loose over time but had been assembled this way at the factory: I could feel that I was tapping new threads into the mounting boss as I turned. Expecting the plastic to be fairly brittle after twenty-plus years, I worked gingerly, and successfully tightened the screw without breaking the plastic.

Transformer with loose crimped tab

While turning the screw, the entire end of the transformer’s cover was rocking from side to side, and a different angle revealed the reason and a second likely suspect for the buzzing sound (of which I carefully took this out-of-focus picture). The mounting cover had an edge bent out away from the laminated core and a loose tab.

After a little work tightening things with pliers and pressure, the cover seemed to be pretty well fastened. I checked the power supply electrolytics with my Capacitor Wizard since I had the clock open anyway, and they all tested good. I reassembled the clock, retesting for buzz several times along the way, and so far the buzz appears to have been banished.

The transformer problem was clearly a manufacturing defect; and it’s interesting to think that it took over twenty years to manifest itself. Here’s to the next twenty!

3 Responses to “Fixing a Buzzing Clock Radio”

  1. ketas says:

    Sometimes, old stuff is better than new.

    Nowadays, both people and electronics tend to take “live fast, die young” approach.
    No, really. One more milliamp, one more degree ‘C, and…

  2. Jo says:

    i too have this clock radio – have had it since 1989 – and absolutely love it. The problem I have is that the radio has died, leaving me only the alarm buzzer to wake to, and I really prefer to wake to music. After your having looked at its internal “guts” do you think I can find someone who could repair the radio portion?

  3. Keith Neufeld says:

    Jo, do you get any sound out of the radio on either AM or FM, or no sound at all?

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