Fault Finding

To fault find or not?

Fault finding is an inductive process if the fault is not apparent during observation. Fault finding is no longer a linear process. If it costs $400 to clearly identify every fault or soon to be realised fault and it costs $600 to replace it; then no one will repair anything. We repair many ovens everyday and most are completed for less than $250.00. Therefore for most people this is a cost that makes good sense.

However, some faults are not so readily diagnosed and can take time to conclude what the cost is going to end up to repair the oven. We have to take a sensible approach and drive toward an economical outcome. So if you want absolute diagnosis please make that clear at the outset and expect to pay for it separate from any fixed price offering.

Good inductive reasoning is very reliant on you the customer. If you tell us the oven is not heating we know the probable outcome will be a new element. Many if not most elements display visual cues that takes seconds to verify it’s faulty. Much like your car tyre. No diagnosis necessary to know a flat tyre. On the other hand, if you tell us the oven is getting too hot we’re not going to be checking your elements! So if you know the element is cracked and falling apart but still working tell us, because we will be most likely considering the thermostat as the culprit.

The worst outcome is your observations simply aren’t correct or are vague. This means we must spend more time going through a bunch of tests that may not be needed. Time wasted equals money wasted! The more you can be sure about what the issues are and clearly communicate them the quicker/cheaper we can resolve your issues.

Need a new Control Board; read on!

Risks associated with fitting electronic parts

So we’ve had quick look at your oven/stove and advised it is likely a “Control Board” fault. “Likely” being the operative word! Because, no one in our industry does diagnostics on a faulty control board. To do this takes schematics and component specifications and expensive test equipment that is better suited to a lab than a van.

Further, the suppliers of the electronic parts will not refund any electronic parts once removed from its packaging. And for good reason, PCB’s are electrically sensitive, and can be damaged by inline electrical parts, or static electricity etc. Suppliers have no way of knowing what happens to the PCB once removed from its package, so they can’t or won’t take these items back.

Deductive reasoning

Not to get to technical; but for most oven/stove faults, we use deductive reasoning. Which basically means we can test certain conditions of a device which will give us a high probability that the device is faulty or not. For instance a fan motor with an open circuit will not work unless the circuit is closed. It’s straight forward, we measure the resistance and we look for a specific result.

Simple example (Wikipedia)

An example of a deductive argument:

  1. All men are mortal.
  2. Socrates is a man.
  3. Therefore, Socrates is mortal.

The first premise states that all objects classified as “men” have the attribute “mortal”. The second premise states that “Socrates” is classified as a “man” – a member of the set “men”. The conclusion then states that “Socrates” must be “mortal” because he inherits this attribute from his classification as a “man”.

Inductive Reasoning

Inductive Reasoning is basically the opposite of Deductive Reasoning. Inductive reasoning starts with a conclusion and deductive reasoning starts with a premise. Inductive reasoning moves from specific instances into a generalized conclusion, while deductive reasoning moves from generalized principles that are known to be true to a true and specific conclusion.

We use this logic to deal with an unrepresented fault. In other words where we can’t specifically test the PCB for a fault, we test the rest. If the rest is okay; then the PCB is the most likely the culprit. Most likely being the operative word!,

But to prove a printed circuit board (PCB) is faulty means we must spend the time verifying the other electrical devices like the are correct. To do this we rely on resistance readings, micro ohm reading, thermal scans, temperature readings etc. This can mean having to isolate each device and verify the correct resistance readings or other readings. Sadly resistance is only one element of ohms law. Which means it doesn’t provide absolute positive proof that the device is functioning correctly. Same with a thermal reading, a low differential reading might imply no cause for alarm. However, using a different cooking function might change the current being drawn is just enough for what is known electrically as the pinch effect to kick in, which can then dramatically vary the differential reading without changing the temperature range. Variables are the crucial factor in determining an unrepresented fault – inductive fault finding.

Economics

Unfortunately the cost of the diagnosis time can be as expensive as the repair itself and generally prohibits an economical outcome.

Example: (not real values)

Call out$100
Diagnosis Labour1 1/2 hour$165
Electronic Board$220
Installation Labour1/2 hour$55
Total  $540

Given the cost of the machine when new was say $650.oo it is difficult to justify proceeding with the above repair.

There are many factors that would drive any final decision, such as age, condition, brand (original value), new price etc. For instance if the machine was just 2 years old and a power outage had caused the PCB to be damaged then it might be sensible to repair the machine. But if the machine was 7 years old and was not in good nick then repairing the machine would not make much sense.

So, the reason this page exists is to save our technician from having to spend 15 minutes trying to explain these details so that you can make an informed decision. And to advise you (the customer) that if you do decide to go ahead and replace any electronic part such as the PCB, we won’t be held liable for the outcome. And once we remove the electronic part from its packaging, you the customer are liable to pay for it regardless of the outcome. Further the electronic part cannot be returned.