I recently received a run of 10 PCBs from a manufacturer in China, and am worried they have begun to cut corners and source counterfeit parts. Here is why:
I had them do full turnkey production (PCB Fab, component procurement, assembly). I've used them in the past and they've been pretty good, albeit with an occasional mistake.
I noticed on 4 / 10 boards, the circuit below not behaving as expected:
On the faulty boards, whereas we expect the gate voltages of Q3 + Q5 to be either ~0 V (if NOR output = 1 (5V)) or ~12 V (if NOR output = 0 (GND)), the gate voltages were anywhere from 3-7 V...
Here is why I'm suspicious of the parts:
- We've used this exact circuit in previous iterations of the PCB, with the same manufacturer, and haven't seen this issue. Only changes are minor difference in PCB layout.
- After I hand-removed Q1 Q3 and Q5, and replaced them with parts I had from Digikey, the circuit functions as expected. I've done this on 3 boards, and all 3 went from non-working to working.
Alternatively if something seems fundamentally wrong with the circuit, I'm all ears. But it is a pretty common, simple circuit, and as mentioned one I've used in previous iterations with no problem.