Trial and errors….

Like most blogs, social media showcases etc. this page is to some extent a massive display of selection bias – you only see the stuff that works, and only when it works. You never (or at least rarely) see the things that don’t work. Because of that, I just thought it would be funny to at least give you a few examples of the memorable mistakes I’ve made during the life time of this blog – along with the lessons I’ve (hopefully) learned from them.

So, in no particular order 🙂
  • Don’t just copy what’s on the schematic – also check what isn’t on the schematic
    A few years ago I was copying a line transformer driver circuit from an article by Walt Jung. The schematic was very straightforward and included a high-speed opamp plus a handful of passives. What it did not show was the decoupling for said opamp and it wasn’t until I had received the finished boards that I realised that. I binned the boards because they were unlikely to be stable, and instead set to work revising the design (while admittedly swearing quite a lot at my own stupidity). The expense wasn’t huge, but the three-week wait for a new board run was a bit annoying…
  • Checking is useless if you rush it
    Also a few years ago I ordered some rear panels from Schaeffer. These designs are normally checked carefully before ordering because they are quite expensive, but I had been so busy trying to close the last designs to get an order out before a holiday that I probably didn’t focus on anything except the mechanical dimensions. So you can imagine my reaction when I received the finished panels and realised that on one of the panels both inputs were marked “channel A”…
    Normally when I finish a design, whether it is PCBs or panels, I don’t order it immediately but try to leave it for a day or two and then go back to it – most of these stupid mistakes that are invisible “in the heat of battle” tend to jump out at you when you’ve been away from it for some time. That process was partly put in place after this incident.
  • Check pinouts and parts carefully
    My first version of the Kuartlotron buffer didn’t work as expected because one of the transistors were drawn upside down in the schematic and naturally I did not catch that. More recently I used an eagle library which I found online for a new part (a special IC). I did think the resulting layout looked a bit strange compared to I was expecting to see, but it was only after quite a bit of checking that I realised the IC actually had its legs miswired in the library. That fortunately only took 20 secs to correct, but it was purely by chance I caught it. I’m honestly not sure how long it would have taken me to spot the problem if I had been working on a finished board, but my guess is it wouldn’t have been easy.
  • Don’t think you’ll remember it later
    A couple of months ago I started on a layout for a discrete preamp design which is coming a bit later. I had real problems getting started on a good layout and I was endlessly shuffling stuff around and not really getting anywhere. The schematic included a trimpot for adjustment which I did not put in originally because I needed to see where the layout was going first and it was in the way. Needless to say I then forgot all about it. This one I actually caught just before submitting the order, but it ended up delaying my order quite a bit because by this stage i had manage to compress the layout so much that there wasn’t really space for adding a trimpot…
    Two lessons from this, one that if there is something that you omit for any reason, it should be written down on a “todo”-list for the design and the other that I have tried doing a more through check against the schematic (partly as a result of the above point as well) before submitting designs.
  • If at all possible, use “prototypes”.
    I’ve lost count of the times where I have been building prototype boards only to realise that there is effectively only one mechanically feasible way of assembling the design because it’s made (too) compact. Quite a lot of the designs I’ve published here carry advice to screw semiconductors to heat sinks before putting in the tall electrolytics that otherwise block the screws, solder SMD parts in a particular sequence etc. Simultaneously you are desperately hoping that the thing works on the first try, because if it doesn’t then trying to troubleshoot and replace parts seems so complicated that you might as well start over from scratch…
    To combat this I have tried to incorporate more “prototypes” into my design process. Not advanced prototypes of any kind, but more simple checks as I go along. This can be using protoboards to verify that the circuit is electrically OK, but it can also be printing PCB layouts at actual size to check component fit (because when they are on the screen what looks like a yawning chasm is in reality often fractions of an inch!). Either way, these steps make it a bit less likely that I end up with nasty surprises when the finished articles turn up – although they are of course not bulletproof by any means.
I’m sure there are more examples, but these are what I can come up with at the moment. Do you see any that you recognise? 😀

2 Responses to Trial and errors….

  1. ksjung88 says:

    Excellent tips! It’s also important to share any mistake we can make all the time for DIY. Thanks for your sharing. =)

  2. Rafael Lino says:

    Thank you for this post, very few people share their mistakes. It’s a learning experience.

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