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I have this circuit my boss wants me to check out:

HEAT ELEMENT SWITCH USING MOSFET

He says even when the "HEATELEMENT" is un-soldered, pins 1 and 2 present a voltage of "Batt" across them and he wonders why. Any suggestions?

One thing I suggested was this thread where the guy soldered his MOSFET upside down: MOSFET Always On despite of Pull-Down

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    \$\begingroup\$ Is the mosfet "on" or is the diode allowing reverse current? \$\endgroup\$ – Solar Mike Jan 28 '19 at 9:44
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    \$\begingroup\$ There could be enough leakage in the MOSFET that a non-zero voltage would be measured, without the load. Add some resistance across 1/2 (like 10K) and measure. More likely the MOSFET is the wrong part, wired wrong or damaged. Also measure R2 from MOSFET gate to source and ensure it's there. \$\endgroup\$ – Spehro Pefhany Jan 28 '19 at 9:53
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    \$\begingroup\$ A high impedance voltmeter probably will always show battery voltage, due to leakage (0.1uA max for the FDD8882). Try with a 1K resistor across 1-2. \$\endgroup\$ – Indraneel Jan 28 '19 at 12:13
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    \$\begingroup\$ The problem is that even when the HEATELEMENT is connected the problem persists and it always heats. \$\endgroup\$ – Stam Echad Jan 28 '19 at 12:43
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    \$\begingroup\$ Have you checked whatever is driving the FET? \$\endgroup\$ – Edgar Brown Jan 28 '19 at 15:11
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Ok so the problem is now solved. The mosfet was soldered wrong. Thank for all your help guys. I really appreciate it.

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