Malfunctioning VT240 - help please - test-drb@ccmp.vtda.org

21 Jun 2020

On 6/21/20 10:41 AM, Jon Elson wrote:

...
  On 06/20/2020 09:41 PM, Charles wrote:
  On 6/20/20 8:31 PM, Jon Elson wrote:

  I confirmed the bad one by removing the piggyback
and the failure 
 returned. Now I need to desolder the bad one without ruining the 
 board. I may just cut the leads off close to the bad chip, and 
 solder the replacement to the stumps. (Normally I remove the legs 
 and install a machine-pin DIP socket). Or just solder the piggyback 
 and leave it there... thoughts?
  Cut the leads close to the body.? Apply a soldering iron to each 
 lead, and pull the lead out with tweezers,
 simultaneously heating and pulling.? This is very gentle to the 
 board, just doing one at a time.? Then, you can vacuum out the holes 
 and install a new chip or socket.

 I've done this many times, and never wrecked a board.

 Jon
  That's how I do it... the vacuuming is the problem. Someday I need to 
 get a good vacuum desoldering station. Right now I just have a 
 spring-loaded solder sucker (which I can do a pretty decent job with 
 on most boards). But this high-density layout (2 traces between DIP 
 pads) I'm a bit wary of.
  Just be gentle, and you should be able to do it.? Also, in some cases, 
 you might heat from the opposite side from the solder sucker.? That 
 way, you can keep the soldering iron on the pad until you have 
 triggered the sucker.? But, yes, the hollow soldering iron with 
 powered vacuum is amazing the first time you try it.? I got one at an 
 auction years ago, it is much better than the regular iron and 
 plunger-sucker.

 Jon 
The small company I first worked for had a Pace unit. I remember not 
being impressed with it - frequent clogs, pads lifting, and not getting 
all the solder out, no matter how we set things. Still beat solder-wick 
though!

I got it done, but pin 16 (which connects directly to the internal-layer 
ground plane) was a bear. From the feel of it and the heat required, the 
draftsman didn't bother to make pad reliefs. Anyway it's now socketed, 
so of course it will never fail again!

I also made a small jumper on a 15-pin D-sub to connect Monitor Present 
L to ground, so that annoying "Monitor Error 9" message stops ;) On to 
the next project!