I am trying to copy a simple PCB I have bought to read an ec sensor.
There is no wiring diagram but the tracks on the PCB are easily visible, so I copied the circuit and upon testing the PCB points, the voltages are too high in places. The PCB consists of some 1k,4.7k,10k,100k resistors, a quad amp, 555 timer, some 103 ceramic capacitors, two 2.2uF caps and two 220uF caps, two 100k trim pots and finally 6 small orange glass diodes which have
ST 41 48 written on them.
I know the diagram I created is correct, I literally sat there for 3 days with a multimeter. The resistors and capacitors, trim pots and quad amp are 100% correct, they were labeled nicely. The timer should have been an NE555P but I could only find a NE555N in store, but I was told it should be fine. So it must be these zener diodes or whatever they are, or my wiring.
The diodes I bought were some 3.3V zener diodes. I tested the voltage going in on each diode on the PCB I bought and it's between 150-200mV and 50mV less out and my PCB is getting 2.56V in the places it should be 200mv or less, it seems my voltage stays the same from the two resistors directly above and parallel to the 555 timer, leading me to believe the diodes are doing nothing as there 3.3 and the voltage is 2.56.