"what is resistance between pin 4 (-Vcc), pin 7 (GND) on genuine LM3886?"
in resistance mode, with an Agilent 1241B, it measures >4 Mohms, with both polarities.
In 'diode' mode, with (+) Lead on Pin 4 (-Vee) and (-) Lead on pin 7, (GND) -- it shows conductance, with drop 0,65V - one diode drop, (forward junction)
When reversed, with (-) Lead on Pin 4 (-Vee) and (+) Lead on pin 7, (GND) -- it shows 'Open'
reassuming: normal use is that Pin4 is negative supply and GND pin is more positive.
When the GND pin goes more negative than -Vee, than somewhere a diode opens.
So, it could be that your multimeter perceives this forward junction as a low impedance short..
Ciao, George
Many Thanks George! Bad news are good news - definitely fakes, in resistance mode both polarities 2,0 Ohm (short is 0,2 ohm), in diode mode 0,1V in both polarities.in resistance mode, with an Agilent 1241B, it measures >4 Mohms, with both polarities.
In 'diode' mode, with (+) Lead on Pin 4 (-Vee) and (-) Lead on pin 7, (GND) -- it shows conductance, with drop 0,65V - one diode drop, (forward junction)
When reversed, with (-) Lead on Pin 4 (-Vee) and (+) Lead on pin 7, (GND) -- it shows 'Open'
reassuming: normal use is that Pin4 is negative supply and GND pin is more positive.
When the GND pin goes more negative than -Vee, than somewhere a diode opens.
So, it could be that your multimeter perceives this forward junction as a low impedance short..
Ciao, George
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