I have two units of a device which I shall call deviceA and deviceB. DeviceB is malfunctioning.
Therefore I compared the resistance values of the same components on the boards of both deviceA and deviceB in order to find the one(s) which have failed. I know this is not the best way to proceed, but being deviceA and deviceB identical, it think it is an acceptable strategy.
I noticed that several components do not share its value with the corresponding component on the other board; I am talking of a 5% to 50% difference.
Then a 8.2v Zener diode, on deviceA it has a 15K ohm resistance, on deviceB its resistance is a some 20 ohm. Therefore I decided to swap the two components in order to check if it was the cause of the defect.
I found now that the swapped components are working the same as before, ie. the 8.2v Zener diode on deviceA it has a 15K ohm resistance, on deviceB its resistance is a some 20 ohm.
Therefore I have to assume there must be some other component on the board which is inducing deviceB strange behaviour.
How would I go on troubleshooting malfunctioning deviceB?
Please let me know thanks.