Malfunctioning VT240 - help please

[Charles]

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!