[sdiy] PAiA 2720/R rebuild

David G Dixon dixon at mail.ubc.ca
Tue Oct 28 00:06:13 CET 2014

> I wasn't meaning to rag on the original kit builder.  We all 
> have to start somewhere and I shudder to think what my first 
> soldering jobs were like.

My original soldering jobs (in my 40s, not when I was 12) were pretty good.
Soldering just always seemed pretty easy to me.  However, a couple of years
ago, I did learn that turning my soldering iron down a little bit (to 350)
really improved the look of my solder joints, using less solder.

> What I don't get though are people who don't mount components 
> flush to the PCB.  I still get DIY repairs where the parts 
> are anywhere from 1/4 to 1/2"
> off the PCB.  

Yes, this is pretty inexplicable.

> I think the biggest issue for first time kit 
> builders is the wrong soldering iron.  When I started many 
> years ago I started with a gun, albeit a small gun.  Later I 
> upgraded to a pencil type but even that wasn't very good.  It 
> had copper tips that just wore out so it was hard to heat a 
> pad.  Finally I found some gold plated tips that worked quite 
> well and I used that iron for many years.

I use a cheap no-name Chinese soldering iron I bought locally five years
ago.  I've never changed the tip.  The tip doesn't look so nice, but it
works just fine.

> I didn't built too much PAiA stuff but I built a lot of 
> Heathkit and SWTPC kits.  Most were pretty good but some of 
> the Heathkit stuff was bare copper PCBs and I remember 
> leaving a lot of flux on those.  I imagine they look pretty 
> bad now as the copper will have corroded fingerprints all over it.
> When I make a DIY on a copper breadboard I always solder the 
> complete pad so there is no exposed copper.  Of course I 
> would rather have a plated breadboard but sometimes I can't 
> find those in the form factor I need.

I etch my own PCBs, and my first bunch were all bare copper.  Yes, they all
corroded (partly because I left a jug of hydrochloric acid sitting on the
floor of my garage behind the desk where my modular sits, and HCl vapors
rose out of the (sealed) jug and corroded everything in the vicinity).  Now
I use Liquid Tin.  I print, etch, drill, then wipe off the transfer with an
acetone-soaked paper towel, then polish with fine steel wool, then soak in
Liquid Tin solution for about 30 seconds.  This plates a layer of tin on the
bare copper.  It doesn't corrode, and it takes solder very nicely.  The
stuff costs about $40 for a half liter, but it lasts forever (if you're
careful with it).

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