Electronics > Repair
Voltage Increase, failed component?
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ajp8868:
Swapped this board to a known working unit and it does the same, so it's 100% a board fault
ajp8868:
Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly
fzabkar:

--- Quote from: ajp8868 on July 29, 2024, 06:04:47 pm ---Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

--- End quote ---

Being a linear regulator, there would be a 7V differential between input and output. A load current of 140mA would dissipate 1W in the regulator.
ajp8868:

--- Quote from: fzabkar on July 29, 2024, 06:31:12 pm ---
--- Quote from: ajp8868 on July 29, 2024, 06:04:47 pm ---Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

--- End quote ---

Being a linear regulator, there would be a 7V differential between input and output. A load current of 140mA would dissipate 1W in the regulator.

--- End quote ---

Meaning..?
ajp8868:
I've tested the 28v side without the 12v side connected and it doesn't increase in voltage - so I'm assuming the 12v is possibly pulling more current than it should - I'll check with the DMM
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