Checking an IC to be sure it's genuine and a not a fake/counterfit

• Checking an IC to be sure it's genuine and a not a fake/counterfit
  Posted by cincin on 17 Apr, 2024 03:16
• I bought an SSM2056 (a hard to find out of production audio EG IC) from AliExpress...
  
  It has arrived, and I'm trying to determine if it's real or not before putting it into my Korg PolySix synth. Luckily I have a few real SSM2056 to compare this new one to.
  
  I went around the legs of a real, known-good one, testing for resistance, and comparing to the AliExpress chip, and things don't match. On many leg combinations that give me no path (OL) on the real IC, I get some high resistance (>6MOhm) path on the new IC.
  
  This tells me that the chips are not the same. But what do I know.
  
  Is this enough to conclude the AliExpress IC is a fake?
  
  cheers!
• #1 Reply
  Posted by ledtester on 17 Apr, 2024 05:00
• Quote from: cincin on 17 Apr, 2024 03:16

  On many leg combinations that give me no path (OL) on the real IC, I get some high resistance (>6MOhm) path on the new IC.
  

  
  "OL" simply means the resistance is higher than some number. For instance, that number could be 8 MOhms in which case your readings of 6 MOhms are pretty close. Your meter's user manual might tell you what "OL" means when measuring resistance.
  
  I'd look into building a test circuit to see if the chip at least operates like it should. It seems the modwiggler.com forum has discussed the ssm2056 chip quite a bit -- you might ask there.
  
  Also, there is this way of replacing a SSM2056 with a PIC microcontroller:
  
  https://electricdruid.net/voltage-controlled-adsr-envelope-generator-vc-adsr-7b/
  
  
• #2 Reply
  Posted by aliarifat794 on 17 Apr, 2024 05:34
• Test the application circuits mentioned in the datasheet. See if they behave accordingly.
• #3 Reply
  Posted by magic on 17 Apr, 2024 06:28
• IMO diode mode is more useful. These things are silicon, so there is plenty of PN junctions in them between various pins. Particularly between power supplies or the substrate and other pins. If these don't match, chances are high that the chip is something else with fake part number printed on it.
  
  Also, does it look like new or used? Are there any signs of black paint or scratching on the top surface?
• #4 Reply
  Posted by cincin on 17 Apr, 2024 14:34
• All very good points! Thank you.
  
  My DMM goes to 40MOhms, but I will poke in diode mode to see, then perhaps build a test circuit if there is still hope.
• #5 Reply
  Posted by cincin on 18 Apr, 2024 04:07
• Well, I looked at the datasheet for specific things to test for, and...
  
  - There very clearly should be a 1K resistance between pin 8 and 9, my real chip agrees, but the AliExpress chip is OL.
  - There should also be a diode between pin 9 and 7 (GND), my real chip says yes, but the AliExpress chip says OL.
  
  I believe that's conclusive enough?
  
  Thanks for the help!
• #6 Reply
  Posted by magic on 18 Apr, 2024 05:29
• Yeah, that's what it looks like.
  
  It is also common that there are many diodes from V- to various I/O pins and from I/O pins to V+ (in this polarity). If the other chips has power supplies on different pins (likely), none of that will match either.