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

[Magnus Danielson]

Aaron Lanterman skrev:
> 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.

*Magnus go over and comfort Aaron as he is curled up in the corner, 
offers him a stiff drink and watches as he relaxes*

I too have made my mistakes. I know the feeling.

> 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?"

Fix it where it is broken. As soon as you let a previous mistake escape 
into the wild, you just add to the confusion. Do NOT fiddle with the 
chips, do NOT do additional modules. Do jumpers on the board.

Dremmel the traces off and use normal wire-wrap to do the jumpers.

We have repaired much worse situations for much higher speed signals 
that way, and we got our boards operational enought to continue the 
debugging.

Cheers,
Magnus