LM3886 fakes??

[krume]

So nobody can answer what I have asked? Very simple question: what is resistance between pin 4 (-Vcc), pin 7 (GND) on genuine LM3886?

 

[asuslover]

krume​

Visually, your chips look like not authentic to me....

 

[Joseph K]

"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

 

[Joseph K]

And his chips visually look like the family of chips with TF package from an italian small webshop in my photos - and those work perfectly in my amps..
but yes, his chips look different than the actual genuine Mouser, RS origin chips in my stack

 

[asuslover]

Joseph's 3886T chips look authentic to me(right side) , Krume's lm3886T chips(left side) don't look authentic to me.
A few differences I noticed .

 

[Joseph K]

Heh, yes, You are right...
butt... 😜
here it is an older batch.. again faithfully well working..
But most probably it still looks a bit suspicious, Krume's chip

 

[krume]

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.

 

[JMFahey]

Agree, bad news but at least now we KNOW what´s happening, instead of endless guessing letter shapes and edge roundness or sharpness.
Measuring RULES