How should I interpret this diagram?

3 months ago by ProfessorHoover to c/askelectronics

I'm repairing an old TV with corrosion on the board. I'm having trouble reading the schematic from the manual. Here's the relevant section: I have two questions:

Do the thick bars on one side of the capacitor and the base of the transistor indicate those are connected together? I'd tone it out but the board is heavily corroded and I'm unsure if they should be connected. I've also seen these bars on other parts of the board, but the components there are not rated anywhere near as high as C451. I feel like that risks high voltage backfeeding through the other parts of the circuit.

What kind of capacitor is C451, and should it be polarised? The BOM lists it as a pp cap which I understand to be non-polarised, but I can't find any key that tells me what the dot on the symbol means. Let me know if I can provide any further information. Thanks

jeinzi 14 points 3 months ago

The horizontal bar is commonly used to indicate ground, meaning the part of your circuit you define to be at 0V. So they are all connected, yes.

I've never seen a capacitor symbol with a dot until now. I only know them on transformer symbols where they are used to denote polarity.

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boaratio 8 points 3 months ago

I believe the dot on the capacitor indicates polarity, and you're correct about the horizontal bar being ground, but a single bar means local ground. Some boards have both local and global grounds.

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ProfessorHoover 2 points 3 months ago

Thanks, I'll tie both of those together and see if I can find a non corroded source for the same ground.

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finalarbiter 2 points 3 months ago

As the other person said, the horizontal bars typically indicate some type of ground. This reference sheet for IEC 60617 calls it "Functional equipotential bonding; Functional bonding conductor; Functional bonding terminal"

That dot typically indicates polarity, though I never remember which side. The dot is often physically marked on the component package, though.

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ProfessorHoover 2 points 3 months ago

Thanks for that link, it'll be useful for me to look up other symbols

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elDalvini 2 points 3 months ago

The dot commonly marks pin 1 of a part, whatever that means for a capacitor. I have never seen a polarised capacitor that is smaller than a microfarad. When choosing a replacement, I would go with an unpolarized capacitor. Even if the original was polarized, an unpolarized one will work.

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ProfessorHoover 1 point 3 months ago

Ok, thanks. I'll get the equivalent part to the pp caps mentioned in the BOM then

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