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How do you start up an untested circuit board?

fmilburn

I've been known to throw a circuit together, apply power to it, and fry something.  Or the circuit just doesn't work and the problem could be anywhere in that mess of wiring.  But I used to work on complex and potentially hazardous projects where we couldn't afford those types of mistakes. There were mechanical, electrical, civil, chemical processing, and instrumentation disciplines, and towards the middle of the design specialists in commissioning and start-up were brought in.

I recently sent out a PCB design for manufacture without prototyping it first.  The schematic is shown below but it is just an example.  My question is more general to starting up any untested circuits.

Schematic

Time for me to get my act together.  I put together a plan with the following approach:

  • Break the circuit into logical sections that can be tested sequentially
  • Describe the test plan for each section with the expected outcome
  • Solder it up a section at a time and test the section before moving on

The actual plan used is shown below.

Commissioning and Startup Plan

One lesson from this was that the test plan should have been made before the PCB was sent out which would have allowed for dedicated test points.  Not shown in the plan (but they should have been) are the bench power over-voltage and over-current settings.

Fortunately, this board went together and started up without a problem but it got me thinking.  What did I leave out?  What tips do you have for planning and starting up an untested circuit?  Do you know of any good resources on the web?

Parents

  • The few boards I have built don't give me the experience to provide a detailed test plan.

    A few suggestions are all I have:

    • I measure resistance between the input power terminal before the board is assembled. NO SHORT!
    • I make the same measurement when the board is populated. NO SHORT!
    • I try to power staging for populating the board. If it involves Arduino or Pi, they are not installed on first power-up.
    • In this staging exercise, I look at what I can populate in stages. Establish the power supply, test, then passive components and test, then active and test and finally processor.

    Like I said my experience is limited so is my knowledge.

Reply

  • The few boards I have built don't give me the experience to provide a detailed test plan.

    A few suggestions are all I have:

    • I measure resistance between the input power terminal before the board is assembled. NO SHORT!
    • I make the same measurement when the board is populated. NO SHORT!
    • I try to power staging for populating the board. If it involves Arduino or Pi, they are not installed on first power-up.
    • In this staging exercise, I look at what I can populate in stages. Establish the power supply, test, then passive components and test, then active and test and finally processor.

    Like I said my experience is limited so is my knowledge.

Children
  • in reply to colporteur

    Good suggestions, using the multimeter to buzz for shorts is the first thing I do too.  Learned from experience :-)  I mentioned it in the test plan but the other thing I do now is a detailed visual between each stage.  Not only have I inadvertently added shorts, but I've also left pins completely unconnected or poorly soldered and then wondered why it wasn't working.

  • in reply to fmilburn

    I've done something similar except on the final PCB.

    I now print the PCB etching and hand trace the layout against the schematic. It is a mind-numbing task especially after working with the schematic for so long. It really takes a lot of concentration and focus. I save this wonderful task for last to preserve my sanity.