A touchy subject - more tales from the bench

Wales · April 24, 2009, 04:59:10 PM

The common theme I detect in this thread is that we all need to step away for awhile and then come back with fresh eyes. Wither we go for a drink, stuff it in box for months, or just avoid looking at it for a while once we get back to it we find the obvious or simple things we missed earlier cause of assumptions.

I can't remember if it was Thomas Edison or Albert Einstein, but one of the two swore by the method that if a problem is giving you trouble force yourself to forget about it and the answer will come to you when you least expect it but it will come. Every day I am coming across situations that make me believe in this more.

It was nice reading this thread to know that the "pros" come across the same problems as me.

My most common DOH! is I forget to put a jack into the input to get power to flow. You can get some crazy voltage reading on the ground when you do this.

frank_p · April 24, 2009, 06:04:46 PM

Arrrgh ! "mechanical" problems.

Arn't we supposed to have electronic failures...

And why when you try to repair your car, it's the "electronic devil" who is comming out...

bluesdevil · April 24, 2009, 08:17:14 PM

I'll add one of mine: I built the Vibratone from Markm's layout gallery TWICE and still couldn't get it to work despite massive amounts of debugging both times. The reason was a ground connection to one of the pots isn't depicted in the layout!! I finally caught it while retracing the schematic a few times. Simple, but it's funny how your mind goes into auto pilot while doing stuff from layouts..... always check with the schematic first, don't take anything for granted and you'll save your sanity.

R O Tiree · April 24, 2009, 08:49:01 PM

Quote from: frank_p on April 24, 2009, 06:04:46 PM

Arrrgh ! "mechanical" problems. Arn't we supposed to have electronic failures...
And why when you try to repair your car, it's the "electronic devil" who is comming out...

I remember my Dad saying to me, when I was very young and just getting into electronics (about 8 years old?), "Always check the mechanical things first."

frank_p · April 24, 2009, 09:17:59 PM

Quote from: R O Tiree on April 24, 2009, 08:49:01 PM
Quote from: frank_p on April 24, 2009, 06:04:46 PM

Arrrgh ! "mechanical" problems. Arn't we supposed to have electronic failures...
And why when you try to repair your car, it's the "electronic devil" who is comming out...

I remember my Dad saying to me, when I was very young and just getting into electronics (about 8 years old?), "Always check the mechanical things first."

Mhhh... And my fluid mechanics teacher also told me: "Learn those formulas, but be aware you'll probably miss your target (plus-minus 40%) due to non-linear behaviours ot matter."

As R.G. is always pointing out: Mother Nature rules everything. But damn, what a temperamental lady she is !

sean k · April 26, 2009, 03:50:57 AM

I couldn't agree with you more Mr Wales! Can't figure it out, can't find it, won't do what its supposed to... forget about it and inspiration will find you.

Want it bad... let it go!

frequencycentral · April 26, 2009, 05:41:07 AM

I discovered yesterday that PT2399 don't work as well if you socket them the opposite way around. Strange that. You don't even get reverse echoes (as I expected you would). Well, it's all about experimentation isn't it. Had I inadvertantly socketed it the wrong way around and discovered that it would pre-echo every note you played I would have been hailed as a genius. It's a fine line between genius and idiot.

Boogdish · April 26, 2009, 09:05:05 AM

Quote from: frequencycentral on April 26, 2009, 05:41:07 AM
I discovered yesterday that PT2399 don't work as well if you socket them the opposite way around. Strange that. You don't even get reverse echoes (as I expected you would). Well, it's all about experimentation isn't it. Had I inadvertantly socketed it the wrong way around and discovered that it would pre-echo every note you played I would have been hailed as a genius. It's a fine line between genius and idiot.

sounds like you were an inch away from inventing a time machine.

I've spent time trying to track down why my pilot light in an amp wasn't turning on, only to discover that I forgot to put the bulb in.

cpnyc23 · April 26, 2009, 01:51:31 PM

Quote from: MikeH on April 24, 2009, 02:01:45 PM
I was looking at it as though the pinout was shown looking down through the casing, when in fact it was the opposite. So it didn't matter how many times I verified the pinout, because I *just knew* that the trannys were in the right way.

I have no personal experience with this... no way. not a chance. nuh uh. that would be crazy. nope.

ok. maybe once.

or twice... or...

-chris

Cliff Schecht · April 26, 2009, 03:33:36 PM

I made a professional audio interface daughtercard for a TMS320C6713 development kit and mixed up a lot of stuff. I blew out two $5 Burr-Brown op amps after finding out that + and - power was flipped, and I laid out and installed my LED signal level indicators backwards. The first LED in the chain was last and the red and yellow LED's were at the beginning of the chain, not the end.. Also, on the digital side, I'm sampling 8 potentiometers that are buffered by rail-to-rail op amps. Turns out the footprint I used for the single op amps (all 8 of them) was wrong.. fixing that was a BITCH but it all works good and dandy now.

This week, I spent a good chunk of time helping the project lab 3 students (this is the RF design lab at Texas Tech) redesign and build their RF oscillators. I ended up completely redesigning and building two projects(including oscillator and buffer) at 435 Mhz and 915 MHz. I wanted to save time so I built everything floating directly over copper-clad board and tried to use through-hole parts where I could. To my surprise, both boards worked on the first try and quite nicely I might add. The 435 MHz one was outputting at 3 dBm before the power amp and so to keep it legal, we left off the power section. The 915 MHz one was quite distorted but still working well - but I couldn't look at any waveforms because the oscopes nearby were all under 500 MHz.. DOH!

newfish · April 27, 2009, 08:50:13 AM

...and the craziest thing about IC sockets is that, out of the corner of your eye, there's something black and 8-legged on your board, so you've *definately* put the IC in, right?

This weekend's boo-boo was some Breadboard-related idiocy. When moving the input cap for a circuit, it helps if you *also* move the input lead.

It was one of those, "well, it was working before I put a different input cap in, so it must be the input cap..." moments.

Strategy · April 27, 2009, 01:48:05 PM

When I was a kid my dad would build synth modules and theremins and stuff for the university electronic music labs he taught in. Recently my parents came to visit and he was inspecting the drum synth clone I built that's currently in the trouble shooting pile. He immediately pointed out a tiny hair of solder that was causing a short between two traces, obscured by a blob of flux I had missed in cleaning the board.

The thing is though my dad is almost legally blind, I'm amazed he could see it. He wasn't looking for shorted traces, he was looking for uncleaned flux which can sometimes obscure problems. Lesson learned, clean my boards more thoroughly, use a magnifying glass to examine and don't do it late at night when I'm exhausted etc.

It doesn't hurt having an electronics-capable parent either!
- strategy

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A touchy subject - more tales from the bench