Epson HX-20, TRS-80 Model 100 Capacitor Kits

[Marvin Johnston]

Hi Alexandre,

I very much disagree with your NEVER use a drill comment and add more 
solder w/heat for several reasons, valid at least for someone who knows 
what they are doing.

First, the little information I could find on the solder corrosion 
caused by leaky electrolytic capacitors suggested a salt compound is 
formed that mere heating and adding solder won't remove. I'd love to 
hear more about this problem and what this residue actually is!

The problem with "keep heating" is the bond between the copper and the 
substrate is substantially weakened by heat making it MUCH easier to 
damage the PCB by lifting traces, remove the plated thru holes copper, 
etc. Not sure about high temperature substrates such as Kapton, but that 
isn't what we are talking about here.

Also notice I used the words "pin vise" and "#62 drill." The idea is to 
use a drill small enough that will remove the residue from the hole 
having enough clearance without removing the copper from the PTH. It 
seems reasonable once there is a hole to solder again and see if the 
hole can be cleaned out.

We lost power at the house today (electric company maintenance) so I 
didn't have a chance to play around more. Also I do have "professional" 
experience with printed circuit boards as I was a field engineer who 
worked in many printed circuit facilities around the US, and owned my 
own PCB manufacturing company in a previous life.

All that said, I still think using SMD might be the safest way to 
replace the caps while minimizing the chance of damage to the printed 
circuit board.

Marvin


On 8/28/2018 2:39 AM, Alexandre Souza wrote:
> never, EVER use a drill. add more solder and keep heating the corroded 
> solder, it will eventually melt and mix with new solder.
> 
> using a drill will destroy the board.
> 
> Enviado do meu Tele-Movel
> 
> On Tue, Aug 28, 2018, 03:38 Marvin Johnston via cctalk 
> <cctalk at classiccmp.org <mailto:cctalk at classiccmp.org>> wrote:
> 
>     Since I have at least four Model 100 and HX-20s, I've decided to just
>     replace all the aluminum electrolytics before repair becomes much more
>     difficult. So far, I see the project as fairly easy depending on how
>     bad
>     the corrosion from the leaking caps is.
> 
>     Is anyone interested in buying a kit or two of the capacitors? I'm
>     guessing buying the parts from DigiKey at low quantity prices will
>     result in about $3.50 or so for the bag of about 13 capacitors. US
>     postage will probably run a couple of dollars or so, but I can also
>     bring them with me to VCFMW. I'll be ordering what I need unless I hear
>     others might want the kits as well.
> 
>     On a similar topic, has anyone given up on cleaning out the corroded
>     plated-Thru-Holes, and just soldered on some SMD caps? If so, how
>     did it
>     work out?
> 
>     Finally, just some observations on the corrosion. I finally found some
>     information about the corrosion caused by leaking aluminum caps. It
>     sounds like the leaking fluid, besides possibly damaging the copper
>     traces, also does something to the solder in the PTH such that a
>     soldering iron won't melt the solder. Right now, the solder doesn't
>     want
>     to melt so I will use a pin vise and about a number 62 drill or so to
>     hand drill out the PTH solder.
>