"Smitty Two" wrote in message
news
In article ,
"William Sommerwerck" wrote:

The problem with bad solder joints and cracked traces is that they are
often
difficult-to-impossible to see.

We recently had a similar problem that was traced (joke intended) to a
cracked trace under an IC.

I would start systematically unsoldering and resoldering every joint on
the
board. It's not enough to melt the solder and push it around. You need to
suck or wick it off, then apply fresh solder, preferably eutectic
(63/37).

No, but it's enough to add a drop of liquid flux to each joint and
reflow it. Solder isn't spackle that you spread around. Wicking off all
the old stuff just to put on new stuff will take about thirty times
longer than adding some fresh flux, which is what you're *really* doing
when you put on fresh solder.

Agreed.

As far as the practicalities of removing old solder go, I have a proper
vacuum rework station which removes solder from a joint almost as quickly as
just resoldering it, but I still wouldn't, under 'normal' circumstances, use
it to remove the solder from every joint on a board before resoldering. I
think that it's probably down to a degree of how much time you have on your
hands and personal preference, if you are an experienced solderer. I only
questioned your original post because you said in it "we recently had a
similar problem ..." I (obviously wrongly, sorry !) assumed that "we"
referred to a repair shop. I don't have a problem with you using this total
removal technique if that's what works for you.

I agree that sometimes a joint which appears to flow when an iron is
applied, may not have reached a correct liquidus state throughout, but as an
experienced solderer yourself, I'm sure that you would agree that when this
happens, it is pretty obvious to the 'knowing eye', and that's the time I
reach for the vacuum iron.

I would however, question the technique from a professional point of view,
for finding *most* bad joints. There are very good techniques for finding
the rogue ones - a can of freezer spray for instance - and a 'blanket'
resolder of an area is always a last resort for me, if all other methods
have failed. Particularly on a densely packed board, a 'blanket job' opens
the way for creating further problems with unintentional ( and unspotted !)
whiskers across joints. With the best will in the world, I think we would
all agree, it happens ...

Interesting to hear how other people go about jobs, and how the juggling act
of practicality versus profitability is looked at and resolved by
individuals.

Of course, there's lead-free bad joints to contend with now, and as we all
know, they defy *all* the proper techniques that we know and love ...

Again, to the OP. As you surmise, you will probably want to screw it back
together before retesting - particularly any screws which pass through the
back panel into phono ( RCA ) socket blocks which have a built in grounding
strap at the screw hole. Some of these AV amps are super-critical of rear
panel grounding, and can cause you no end of problems with the protect
circuit cutting in with the slightest disturbance, as ground connections
come and go ...

Arfa