More on my flickering DEC monitor

From: <(>
Date: Tue Mar 23 13:52:39 2004

> I'd say either those components shown in solderside.jpg were replaced
> at some point, or the person doing the hand-soldering wasn't
> particularly competent. More likely the latter since the signs are
> there at every pin that's a hand-soldered part, as far as I can see.
> It doesn't look like re-melting as you suggested. So it's not that
> solder has escaped from the joints, it's simply that more was
> originally put on it than the rules of good workmanship call for.
> Look at D910 (a bit further to the right on that photo) for an example
> of good work. (I think that one is the wave solder machine at
> work...)


> The brown gunk looks like flux (rosin) that wasn't cleaned off. The
> solder joints have more solder on them than they should, but not so
> much that you'd get solder bridges as far as I can see. Excess flux
> can cause corrosion and leakage current, but I don't see corrosion
> here and some leakage is not all that likely to be an issue for a
> power circuit such as this.

I'm curious what a leakage and corrsion looks like with flux left on
the circuit board?

> It probably wouldn't be a bad idea to re-heat those joints with a
> piece of Solder Wick to suck up the excess solder, and then clean off
> the rosin with a suitable flux remover. (Unfortunately the good ones
> are all Politically Incorrect. Maybe acetone would work, I haven't
> tried lately.)

Actone from paint dept works well. Get a box of swabs (Q-tips is
best, generics sucks; excuse me).

> The dark spots on the board seem reasonable. Those resistors are high
> power wirewound units, those get *very* hot in normal use. Raising
> them -- and high current diodes like D907 -- off the board is a
> typical trick to get better cooling. The radiated heat tends to
> discolor the board at some point, that isn't necessarily an issue.

I call those golden brown spots as slow bake. Perfectly normal.
Real black and crumbling (always when a part fried) is no good, has
to dug out. I do sometimes on the TV & monitors at work. I work for
a electronic repair shop daily.

> Something to look at, though: on the "solder.jpg" picture I wonder
> about the funny rings on the right solder joint of R923 and R924.
> That may just be a shadow, or it may be a mechanical problem in that
> joint. It wouldn't hurt to find joints like that and re-melt them.

This is called fractured joints, fix them. Before soldering,
get a pink eraser or rod eraser that can take off oxidization on old
penny, give it a few scrubs over those suspect joints including the
component lead to break the oxide barrier to let solder wet properly.
Blow out the eraser crumbs.

Remove the CRT tin cover, you will see some cracked rings on many
parts too. Ditto to any hot parts, heavy parts and/or large pins.

Those soldered joints I made looks like factory originals and
extremely shiny, wetted, sometimes looks black due to flawless shine.
Ditto no sign of flux, I clean them depending on products, if it is
junky or too little estimate, do good job but no clean up. Those
excess solder in that photos is sign of a rushed, lazy tech.

What kind of digital camera taken those outstanding photos that
showed those cracked rings in those solder side joints?

Even sony who reworked their stuff, still is sloppy. :-)



> paul
Received on Tue Mar 23 2004 - 13:52:39 GMT

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