Hello i have been trying t reverse engineer a EC sensor pcb for the past week and i am stuck on just one part being the switching diodes. with a magnifying glass i see ST 41 printed on the glass diodes but nothing more, so i when out and bought some 1n4148 switching diodes, they the pcb does not work so today i got some ST 41 48 diodes from ebay with no specs and now i get a reading on my arduino of 0.65 using ecValue = analogRead(1) * 5.00 / 1024, 2; but it does not change, this is progress as with the 1n4`48,s i was getting 0 all the time. before you ask yes the polarity of the diodes is correct on my pcb, So my question is who many different types of 41 version switching diodes are there ? what do you think is wrong the forwarding voltage or amps of the diode? Is there any way i can test the diodes on the WAI pcb to find their specs ?
The diodes may be Zeners?
The best way to figure out which type the diode are is to test them for maximum ratings with a welder. 
You could measure voltage drop etc. but there is not much else you can do. (IMHO)
i tested the voltage drop with a digital multimeter in diode mode and both the St 41 48 diodes im using and the St 41 diodes on the other pcb both get 0.6 in both directions - polarity ? is that any help identifying them?
I cannot identify diodes given the voltage drop :o
Some others on this forum probably have the required skillset?
@Robin2 possibly
Please upload pictures so we can see the exact part.
Thanks
All the voltage drop tells you is the material it is made from, in this case silicon. But if you measure the same in both directions you do not have a diode. Maybe your measurement technique is wrong. How are you doing it?
Google tells me that an ST41 is a 3.3volt stabistor diode, whatever that is.
Type of low voltage more accurate and sharper cutoff zener, used for voltage clamping and input pin protection.
Not sure if a 3.3volt standoff TVS diode is the same.
Leo..
yay i got it working i had a micro break in a connection on my pcb i etched. im happy now i had spent a while on it and i was worried i had done something else wrong. Thank you all for the help.