I have been working on electronics for over 35 years and never seen anything like this. While going to repair a JC Penney AM/FM Stereo/Cassette/Clock Radio Model 680-3796 Catalog # 850-1793 FCCID:ANV9UD680-3796 which only has sound out the right speaker, I connected my oscilloscope to a leg of the left speaker that has no output and saw 120 VAC, 60 Hz. I unplugged the radio and when inspecting the bridge rectifier board saw that they designed the clock radio to have a 2.2 MΩ Allen-Bradley 1 Watt 20% resistor tying 120VAC to the common of the DC side of the bridge rectifier. This connection to common through the 2.2M resistor makes everything inside the radio float on 120VAC.

I am tempted to clip this resistor out to remove this stupid floating 120 VAC but before I do so I figured I would ask someone who is more knowledgeable than myself as to if it has a required purpose or not for the filtration somehow as to me it makes absolutely no sense to have your secondary side of a transformer with the bridge rectifier tied to 120VAC Main through a 2.2 MΩ resistor. The red wire that runs from main power from a strange small daughter board to around back side of 2200 uF, 25 V cap to leg of 2.2M resistor of the filtered bridge rectifier board is where it gets its 120 VAC. In the hundreds of radios I have repaired I have never once come across something so odd. It was only with old tube sets and non polarized plugs that you had to ever worry about a floating 120 VAC inside a radio and this is all 1982 technology with mostly analog components as it was manufactured October 1982. Normally your secondary from transformer is isolated from primary side mains and you have a nice filtered DC output from the bridge and its filter caps.

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1 Answer 1


I think because it is designed to work on a 2 pole outlet with no incoming earth, and the internal circuit needs to be referenced to something. Typically if you had an incoming earth the internal 0V would somewhere be tied to that, possibly via a resistor. But they don't have that here so they tie the circuit to LINE. As the case is presumably completely plastic, they can do this.

If you would inadvertently place yourself between the circuit and ground, you could receive a maximum current of just over 150uA. This is way lower than the lethal current for humans, which is in the order of mA. Without this resistor, the secondary circuit might float over time to almost any voltage, limited only by the breakdown voltage of the transformer or the physical enclosure, which will be much higher than 240V. So tying the internal circuit to a defined potential is in fact a safety feature.

  • \$\begingroup\$ Was thinking, maybe this was manufactured sloppy with low cost labor and the brown cord with polarized 2 prong plug really should have been soldered to the small daughter board to the Neutral Leg. As this would I feel give it a better earth ground reference? As Neutral is tied more directly to ground vs floating line of the Hot side. Additionally was thinking for ESD purposes even though plastic case maybe the cassette player can van de graaff and create some sort of static potential as well as a user shuffling feet on carpet before moving a switch or pot knob that maybe this is the purpose? \$\endgroup\$
    – Sam07628
    Sep 26, 2022 at 18:00
  • \$\begingroup\$ depending on where you are in the world, neutral may or may not be "earthy". It could be just as "live' as the pin marked live. Yes, you definitely do not want the internal isolated electronics to be completely floating. Please mark this as answer if you feel it has answered your question adequately. \$\endgroup\$
    – danmcb
    Sep 27, 2022 at 12:16

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