Faulty (possible counterfeit) 74LS04 chip

CPUville Bus Display Kit possible bad part (fake, counterfeit) 74LS04 chip

Today 2021-09-16 Donn from CPUville contacted me and informed me about a faulty (maybe counterfeit) 74LS04:

It has come to my attention that a part in the Bus Display Kit may be faulty. The part in question is the 74LS04 IC that goes into the U3 position. This IC is used to generate the slow clock signal and logic signals for the LED output ports. The problem that was reported by two customers is that this IC was getting hot and the slow clock was not working (not cycling). I did some experiments and found that the chip that fails has an odd logo on it. I contacted my parts supplier (Jameco electronics) and in discussion with their tech department we believe that the faulty chips may be counterfeit. The logo may be a poor copy of the Texas Instruments logo (see photo of a probably genuine TI chip). The faulty chips do work as signal inverters, which is the test I perform before accepting them into my inventory. However, they fail to operate in the slow clock R-C oscillator… (Donn Steward)

I found on my bus display board also one chip with a bad logo and decided to test the chip and compare the chip with a spare part because my chip wasn’t getting hot and seemed to work.

IC Comparison

Good chip (manufacturer’s number is 79AC6DK):

"SN74LS04N - good logo"

Bad chip with the bad logo (possible counterfeit) (manufacturer’s number is 19ARSS8):

"SN74LS04N - bad logo (possible counterfeit)"


I compared the original one with the counterfeit chip with an oscilloscope. For the test I build two slow clock circuitry on a breadboard and attached an oscilloscope on both chips for comparison. Both seemed to be nearly identical. So my chip seems to be o.k. but I don’t trust it because of the bad logo. I marked it as bad and put it into my storage box of bad chips. I highly recommend the linked video “‘Fake’ chips?”.

Post Update

  • 2021-10-24: I found some more possible counterfeit ICs with the bad logo on the Z80 Single-Board Computer, a 74LS04 (19ARSS8) and a 74LS92 (19ATEJK). The board is working perfectly, but I decided to replace these chips with original TI / Renesas chips.
  • 2021-10-21: Add link to CPUville - News and Issues - Possible counterfeit ICs?
  • 2021-10-21: Add link to heise online article “Retro-Ersatzteile: Knopfzellen, (Fake-)Chips und Böller”.