sbelyo Posted July 9, 2014 Report Posted July 9, 2014 I have several OPA627 and OPA637 in 8 pin dip. Some I ordered from digikey, some from ebay that could've been digikey samples and some from ebay that aren't. The problem is I acquired some when there were some fakes going around. I didn't separate one order from another and put them all together. I'm sure some are real and some are fake but is there a definitive way to tell?
Mister X Posted July 9, 2014 Report Posted July 9, 2014 Measure the resistance between the V+ pin (7) and each of the "trim" pins (5 and 1). The real ones should all be pretty close, the fakes will not be.
sbelyo Posted July 9, 2014 Author Report Posted July 9, 2014 There's a thread on HF about it. I remember that thread and I think I went through it only to have more questions.
sbelyo Posted July 9, 2014 Author Report Posted July 9, 2014 Measure the resistance between the V+ pin (7) and each of the "trim" pins (5 and 1). The real ones should all be pretty close, the fakes will not be. I'll try that tonight. I'm sure one or two are fake because the logos aren't straight. I'll see what happens
DefQon Posted July 9, 2014 Report Posted July 9, 2014 I'll try that tonight. I'm sure one or two are fake because the logos aren't straight. I'll see what happens I've had samples from Ti and Analog Devices where the logo weren't straight. As mentioned resistance measurement and possibly even listening can point out the fake from the real pack.
sbelyo Posted July 10, 2014 Author Report Posted July 10, 2014 (edited) I have batch 1 1 637BP that's 220 Ohms off 1 637AP that's 400 Ohms off 1 627AP that's 170 Ohms off I have batch 2 1 637BP that's 0 Ohms off (dead even) 1 627BP that's 80 Ohms off 1 637BP that's 10 Ohms off What do you think? Edited July 10, 2014 by sbelyo
DefQon Posted July 10, 2014 Report Posted July 10, 2014 Could be factory rejects. Maybe try giving them a listen and see if you can point out any discernible differences apart with your ears.
sbelyo Posted July 10, 2014 Author Report Posted July 10, 2014 There's this as well... Try red on pin 1 and black on pin 5, then black on pin 1 and red on pin 5, both measure should read 45-55K
nikongod Posted July 10, 2014 Report Posted July 10, 2014 Did you try a similar test (measure with red and black probes one way, then switch them) for the 5&1:7 test? Meters sometimes switch diodes/transistors on and mess everything up. Looking at the datasheet for the 627 I have no idea how this would happen in real life, but it is easier to check both ways than think about
sbelyo Posted July 10, 2014 Author Report Posted July 10, 2014 Did you try a similar test (measure with red and black probes one way, then switch them) for the 5&1:7 test? Meters sometimes switch diodes/transistors on and mess everything up. Looking at the datasheet for the 627 I have no idea how this would happen in real life, but it is easier to check both ways than think about I did not keep track of red or black on the 5&1:7 test. I will retest when I get home as well as test between 5 and 1
luvdunhill Posted July 11, 2014 Report Posted July 11, 2014 Measuring resistance with a handheld meter seems like an odd idea. What about comparing slew rate?
sbelyo Posted July 11, 2014 Author Report Posted July 11, 2014 Measuring resistance with a handheld meter seems like an odd idea. What about comparing slew rate? I have never done that bfore. Does require a scope and a signal generator?
luvdunhill Posted July 11, 2014 Report Posted July 11, 2014 Large and small signal response would be good as well. The real question is how good are the fakes? If they are good enough to best your measurement equipment (the real ones likely will) then its not a feasible test. The question is how large is the gap...
sbelyo Posted July 12, 2014 Author Report Posted July 12, 2014 batch 1 difference between 5&1:7 both ways 1 637BP that's 220 Ohms off 1 637AP that's 400 Ohms off 1 627AP that's 170 Ohms off Measurement of resistance between 5&1 all fall between 45 - 58K both ways batch 2 difference between 5&1:7 both ways 1 637BP that's 0 Ohms off (dead even) 1 627BP that's 80 Ohms off 1 637BP that's 10 Ohms off Measurement of resistance between 5&1 all fall between 45 - 58K both ways I'm ready to call them all real. I have no other means to test other than to listen to them in a circuit. What do you think?
DefQon Posted July 12, 2014 Report Posted July 12, 2014 If there is a small etched part code number you can maybe email Ti to confirm its authenticity. Other then that you can test or listen.
sbelyo Posted July 12, 2014 Author Report Posted July 12, 2014 yes, they all have a code, I'll email TI on monday to see what they say
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