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

[Jerry Gray-Eskue]

Aaron,

I would socket the parts, especially the ones I want to reuse (7 expensive
vactrols).

The op amp pin reversal can be corrected by bending the input pins up away
from the board and using these as solder points. if you can abandon these op
amps to the board I would solder short wires in the PCB where the (wrong)
pins would go, solder the op amp into the board ( With the "wrong" pins bent
up and away ) and attach the wires to the correct input pins.

The important thing is to make this last "mistake" board, to do this you
need to make at least one of the boards fully operational no matter how much
"kludge" it takes and be sure that each correction makes it into your
schematic. This also allows you to prove out the design and know that any
changes you made are working as expected, so you prove out the corrected
schematic and the design is validated.

This is all a normal part of the design cycle, I usually try to build my own
prototype PCBs to keep the cost of this design phase down, I use the same
artwork the production boards will be made from, and still order a
evaluation quantity on the first pass, just in case there is any problem
with drill sizes art work or other manufacturing issue.

- Jerry

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Aaron Lanterman
Sent: Saturday, June 20, 2009 11:12 AM
To: sdiy DIY
Subject: [sdiy] PCB layout mistake = Aaron curls up in a ball in the
cornerand 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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