[sdiy] PCB layout mistake = Aaron curls up in a ball in the corner and cries

[David G. Dixon]

After hearing the sob stories, I'm definitely going to stick to my method of
laying out one-sided boards by hand, and etching and drilling at home.
Laying out by hand, and then counting parts for the BOM, one typically
catches circuit blunders before immortalizing them in copper.  I've made a
few blunders, but even in the most severe cases where I've decided to make
an entirely new board (mostly for esthetics), I can usually salvage every
single part safely, right down to the jumpers (no through-hole plating, and
I always use IC sockets), and be up and running again later that same
evening.  I don't think I'd even be doing this hobby if I couldn't make my
own boards at home.


> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of Aaron Lanterman
> Sent: Sunday, June 21, 2009 12:12 AM
> To: sdiy DIY
> Subject: [sdiy] PCB layout mistake = Aaron curls up in a ball in the
> corner and cries
> 
> Feeling overly confident from the success of my Music Easel LPG layout
> (youtube video to come when I get around to it), I was really excited
> when five new boards (preamp & env det, pulser, envelope generator,
> timbre circuit, and balanced modulator) came from PCBCART last week,
> and I happily built, built, and built. I need to order a few strange
> resistor values and various pots, but I'm close to being able to start
> testing everything.
> 
> Then, while viewing the schematic of the timber generator, I realized
> to my horror that I had the +/- on four op amps switched. The feedback
> was going the wrong direction. How could I have not seen that before
> in all the time I've spent staring at the schematic? Hmm, I'll need 8
> jumper wires to fix that. Bad, but still doable.
> 
> Then I reviewed the others. The pulser, envelope generator, and preamp
> & envelope detector have op amp inputs OK. But on the balanced mod -
> oh hell, I screwed up the inputs of 11 of the 12 op amps. Aaack, that
> would require 22 jumper wires! *hits head repeatedly into wall*
> 
> What makes it worse is I have a vague recollection of actually
> switching the op amps from the correct way to the wrong way at some
> point in a severe brain fart moment.
> 
> AAAAAAAAAAAAAAAAARG!
> 
> That's a couple hundred down the drain.
> 
> I figured it out before I started testing, but I still have most of
> the parts in. My plan is to solder in the vactrols with only a few
> leads in, so I can clip them back out and reuse them (I can't imaging
> committing 7 expensive vactrols to a board that requires 22 jumper
> wires, which I can't imaging are very stable).
> 
> But I do want to try to test everything, so that when I fix the op
> amps I can fix other mistakes I find to.
> 
> So what's the best approach to actually getting a prototype running?
> 
> 1) I was thinking of dremelling the traces, but then I thought a
> quicker solution would be to just clip the input leads on the ICs
> where the ICs meet the board.
> 
> 2) If I take approach 1, is there a "best practices" for soldering
> jumper wires on top of ICs? I imaging it will be hard to make a stable
> connection
> 
> 3) Instead of 1 and 2, maybe I should unsolder the op amps (I
> generally solder chips straight into the board without sockets, unless
> it's a particularly expensive chip to replace, or failure prone like
> CMOS), put in sockets, and build some "pin switchers?"
> 
> - Aaron
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