[Coco] Resurrecting a dead CoCo 3

[RJRTTY at aol.com]

In a message dated 1/9/2009 4:13:43 P.M. Eastern Standard Time,  
jet.pack at ymail.com writes:


>Recently, I acquired a CoCo 3 that had been killed by it's previous  owner. 
An apparent attempt at repairing 
>the CoCo 3 by replacing I.C.'s at random resulted in the destruction of  
many PCB traces. The actual >problem 
>with the CoCo 3 was relatively simple and I'll point that out in a  moment, 
but first, I had to reconstruct the 
>damaged circuit traces.After a few hours with the CoCo 3 Schematic, a  
notebook and an Ohmeter, I had 
>ascertained all traces that needed to be reconstructed. I began by  
desoldering every I.C. left on the board 
>that didn't have sockets and replaced them with sockets and plugged  those 
I.C.'s back in (a step that >wasn't 
>needed, but I wanted to socket all the chips to make future repairs and  
experiments simpler.) Next, I took 
>my notes and some kynar wire-wrap wire and repaired all of the damaged  
traces as noted with the help of 
>the Ohmeter, and I then placed sockets where those I.C.'s went and  plugged 
them back in, except for the 
>CPU

>which I replaced with a 63B09E. Since this board has the 1986  G.I.M.E., I 
went ahead and replaced the 
>capacitor C64 with a quality WIMA 220pf capacitor, although this  probably 
wasn't necessary. I then >plugged 
>the Performance Peripherals 512K Memory Board Back in, hooked  everything up 
and turned it on. It didn't 
>work, of course, because the original problem that caused the previous  
owner to destroy the board in the >first 
>place must still exist. What was that problem? Well, quite simply, the  GIME 
only needed re-seating in it's 
>socket - I took it out, cleaned the pins and socket contacts plugged it  
back in and voila - working CoCo 3 
>512k fully socketed chipset :)
 
Nice job.  What people don't take into account is that the integrity  of the 
bond
between the traces or pads is lowered each time the soldering or  desoldering 
iron
is applied.    You can't just continuously stress the traces  and pads like 
that
in an endless "fishing" expedition looking for a problem.     Sooner or later 
they
will lose their grip and come off.     In situations  like this you should 
install a
socket whenever you have to replace a chip and keep heat stresses on the  pads
and traces to a minimum.  
 
And of course you should eliminate the simple and easily tested  potential
causes of the problem first before moving to the complex ones...
 
If you are not a technician by trade you should think of being  one.....
 
Roy
 
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