when solder won't stick?

Cartouche

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I'm working on this WG 7905 chassis. New HOT, cap kit, flyback.

On a couple of the solder points, the solder won't take. It's happening in areas where that orange waxy goo that the manufacture pours on that white adjustment knob (vr6/shutdown area) has run into the holes that the legs of the components go through. (1st photo) One resistor had a terrible joint, so I sucked it up, now solder will not stick to the trace hole. (2nd photo)

What's a way to get down to a surface that will hold the solder? I've heard of fiberglass pencils?

How about the lifted trace in the third picture, it's one of the holes for the horizontal output transformer. Is there some epoxy used to get it back down? (3rd photo)

Thanks, Marc
 

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What's a way to get down to a surface that will hold the solder? I've heard of fiberglass pencils?


Marc,

Go to Sears and get their 3 tool soldering kit and use the stell brush and scrapper. Also pick up some liquid rosin. Just a drop will do. This combination should do the trick. And yes, a VERY light amount of high temp epoxy for the trace.

Saltbreez
 
It's hard to tell with all that flux on there (you need to scrape that all off and clean it up with alcohol and a brush), but it looks like you may have lost some or all of the pad.
As for that lifted trace, just cut it off and scrape the green masking off what remains... you're going to have to solder a copper link in there to repair that.
 
The solder won't adhere (create an amalgum) if the joint is dirty or tarnished. I recommend wicking all the old solder and starting over. Get yourself some acetone and some lint-free wipes (I use Kimwipes and they work great). After all the old solder has been removed, clean an polish everything really well with the acetone and wipes. All joints should look shiny. Reinsert each thru-hole part and add a small amount of flux to the joint. Then solder. Be sure your iron is hot enough to finish the joint in about 2-3 seconds, but no hotter! Use enough solder to cover both the pad and lead, and you want a nice, shiny joint that looks concave. (Mt. Fuji I think someone described recently. :D) Finally, clean up with the acetone and a wipe again. Done!

For the pulled trace, you need to cut it back to where it is still adhered to the board. Then scrape away the green solder mask and tin it (put solder on it). Leave a mound of solder on it, and make sure you've covered all of the exposed copper trace. Insert the leaded part and bend the lead to the solder mount. Solder, trim the lead, clean up, and done!
 
Maybe I have the heat too high on my Weller. It melts the old joints almost immediately after contact. It's a WLC100 set to about "4". I do get pretty nice Fuji joints when I solder.

So to summarize, I need to:

1) remove solder from bad joint (by desoldering and suction)

2) remove corrosion, goo from traces and pads
(Dab with acetone soaked q-tip, then it wipes clean with lint-free wipes? Or will I likely I scrape with an exacto blade or similar scraping tool?)

3) rebuild traces & pads
Ever tried this? It looks easy.
http://www.youtube.com/watch?v=XEV_3etdIL0

Thanks,
Marc
 
Maybe I have the heat too high on my Weller. It melts the old joints almost immediately after contact.

That's not necessarily a bad thing. The 2-3 second rule is a better indication.

2) remove corrosion, goo from traces and pads
(Dab with acetone soaked q-tip, then it wipes clean with lint-free wipes? Or will I likely I scrape with an exacto blade or similar scraping tool?)

Scrape only if necessary. Acetone and elbow grease should work in most cases, unless the solder flux has been set for quite some time. Then it can be like glue and you'll need to *gently* scrape. A dental tool is great for this BTW.

3) rebuild traces & pads
Ever tried this? It looks easy.
http://www.youtube.com/watch?v=XEV_3etdIL0

No access to youtube here at work unfortunately. :(
 
3) rebuild traces & pads
Ever tried this? It looks easy.
http://www.youtube.com/watch?v=XEV_3etdIL0

Just watched this over lunch. I've never tried the solder pen, but it looks like a mess waiting to happen. :p I've had more decent luck trimming the broken trace, and then soldering in a shunt of hookup wire. It looks a lot nicer too.

For your broken trace, I still recommend bending and soldering the lead directly to the exposed board trace. Reason being if you use a solder pen or hookup wire shunt it might not give you enough current-carrying capacity for that big fat power trace. Instead, a solder mound with the component's lead should give plenty of capacity, and prevent that thing from over-heating during operation.
 
Yes, get some liquid flux. Make sure it's the liquid and not solid flux. For cleaning flux, I use 99% alcohol. It's easier for me to get. And not quite as scary in case there are kids around. Or if you have a habit of eating while doing cap kits. Acetone tastes like burning!! :p Alcohol and q-tips. For large areas, or where there are lots of pins to snag the cotton, I use a soft tooth brush to scrub it.

I agree about the solder pen. That looks a lot like a combo of the paint markers and solder paste syringe that I have. Very messy, very hard to get right. For repairing broken traces it's hard to beat a solid copper wire jumper. I actually used to keep a pile of trimmed component leads just for future trace repair.

For the trace, if you solder the component lead directly to the trace, you might want to add a bit a glue to hold the component. Especially if it's heavy. If it moves a lot it can further damage the trace.
 
I don't think that's goo....that's missing traces/pads. Solder won't stick to something that's not metal.

Edward
 
Those solder joints on the heavier traces look like you don't have a hot enough iron... or an iron that can maintain the temperature when dealing with heavy traces.
 
Some good replies seen on here so far. My only comment, and I mean this to be helpful and not critical of anyone, is that I've never used a solvent as aggressive as acetone on a PCB in my 30 years of experience. Straight cheap 99% rubbing alcohol will serve you very well. It smells less, costs less, won't eat plastic components or remove the solder mask, won't go right through your skin, etc. etc. It will however clean and degrease and dry without leaving any residue and it will remove rosin and no-clean fluxes very well. Q-tips & alcohol is a fantastic combination and is always sitting on my bench. I use acetone to strip heavy adhesive and old paint from control panels and stuff like that. Leave it in the garage. It has no place on a proper electronics bench... in my opinion.
 
Interesting. I've used both for years and I've found acetone to be much better at cleanup than iso alcohol. Also never had a problem with it eating anything it wasn't supposed to.


Some good replies seen on here so far. My only comment, and I mean this to be helpful and not critical of anyone, is that I've never used a solvent as aggressive as acetone on a PCB in my 30 years of experience. Straight cheap 99% rubbing alcohol will serve you very well. It smells less, costs less, won't eat plastic components or remove the solder mask, won't go right through your skin, etc. etc. It will however clean and degrease and dry without leaving any residue and it will remove rosin and no-clean fluxes very well. Q-tips & alcohol is a fantastic combination and is always sitting on my bench. I use acetone to strip heavy adhesive and old paint from control panels and stuff like that. Leave it in the garage. It has no place on a proper electronics bench... in my opinion.
 
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