2 in 1 testing

Hi all, I’m a new zynthian builder and I’ve just done my first bit of pcb soldering. The 2 in 1 controller and I’m not completely happy. I’ve finished it all according to plan and all the visual checks look OK. But i’m not confident in my soldering. I’m professionaly a software engineer so i’m used to unit testing. I desperately want to unit test my 2in1 board. But to do that I need a clear idea of what the board is supposed to do and I can’t see that anywhere. Can anybody tell me how to test the 2in1? I will continue with the rest of the stuff so I’ll find out in the end anyway if it works or not. But it feels to me that it would be useful to be able to test the pcb? Is this a worthwhile thing to try?

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Hi, done lots of soldering so here are my tips:

  1. Clean board with Alcohol, 90% is best but 75% will do with a bit more work. Use an old toothbrush to work out ‘hard’ flux.

  2. Inspect with a magnifying glass. Looking for dull bumpy joints or hairline crack in joint or bridges between pins or leads. The solder should have flowed onto the board and pin with a nice shiney concave fillet, if not reheat and reflow it. Bridges can be fixed with solder wick.

  3. Continuity check using a multimeter, either use the Ohm setting or the Audio Continuity setting (if included). Touch one test lead to the header pin and the other lead to the connected part’s lead, Listening for the tone or look for a zero reading on the meter. For example: The header pin #1 is 3.3V and connects to one leg of C2, one leg of R1 and Pin8 of the 6n138, these would be called a net. Some nets have only 2 nodes and others have many nodes like the GND net. The idea is to pass the continuity voltage through all solder joints, one at a time, to confirm they are really connected and not a ‘cold’ joint. The circuit drawing PDFs are here:
    https://github.com/zynthian/zynthian-hw/tree/master/PCBs

  4. Last, before connecting power, using the multimeter in Ohm setting test for shorts. Gnd to Vcc, GND to 3.3V are the most important but you can also check between IC pins for bridges, but sometimes two or more IC pins are meant to be connected such as MCP pins 3, 4, 5, 6 & 9. So work with the PDF. The point is to avoid a dead short.

After all this you can be pretty sure the board will work, but if not most likely it’s a bad/wrong component or IC installed wrong. The 2 in 1 board isn’t too complicated, take your time till you get more confident. Circuit tracing will also help you when you crimp the cables, as a faulty crimp can be detected with these same tests. I test all IDC crimps I do, just to be sure :slight_smile:
Yogi

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Excellent. Thanks very much. Would you say this is general practice or just for insecure people?

Well for me it’s general SOP. When working on a complex project, waiting till it’s all built and interconnected is asking for lots of headaches. Best to test sub systems, at least for wiring errors, on an unproven design. So if it doesn’t work and you know it’s built as designed, troubleshooting is restricted to an error with the design rather than a mistake in the build.
Of course a lot of my projects are point to point wire on perf boards, so lots of room for dumb mistakes.
Yogi

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