cheap time controlled relay board. No voltage regulator?

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gabeNC

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I'm troubleshooting this board for a friend. The board seems to work except for the relay, doesn't trip when the timer is up. It's super cheap but we are looking at it from a educational perspective. My question is... where is the voltage regulator for the mcu/low voltage side of the circuit? According to the datasheet, that MCU is rated for a max of 7.5 volts. There is no transformer, walwart or otherwise.

thanks.
 

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Transistor Q1, 3 Zener Diodes ZD1, ZD2 and 1 more, 10 K Resistor R8 - all or part maybe part of a voltage regulator.

Ramesh
 
It looks like it may have a dropper capacitor type power supply, but I would need to see the track side of the board to be sure. As well as the parts listed by Ramussons, you also have C2 and C3
 
What is the input voltage?
The relay is 48 volts DC it may be powered off rectifed mains voltage.
 
The input voltage is 110. There is no isolation, that relay and large polypropylene cap seem to be it. I'll follow the traces and post a pic of the back.

thanks gents.
 
It's possible that the relay coil itself is goosed, check the resistance across the relay coil and if that seems ok, check the voltage across it when it's supposed to be on and off. Watch your fingers if it's on mains I suspect that the dropper capacitor is providing enough current to allow the micro to run, but just not quite enough to pull in the relay, but a voltage check will confirm that.
 
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