bit OT: tips wanted for changing mobo capacitors

[Mars Amp Repair]

desoldering thru holes & double sided pcb'x

Folks,
The only way to do this with guaranteed results always is with a product called ChipQuik. http://www.chipquick.com/
It is fairly expensive but short of spending the $600 for a vacuum desolderer, this stuff is the bomb. I've used it for years on Flatpacks up to 114 pins ( a must for keyboards) as well as any type of thru hole components. It will save your tearing up the clad when you're not certain you've got all the solder out.
It is a high lead per tin composition & melts at a relatively low temp. It stays molten while you add it to all the pins of a flatpack or thu hole component. Once you have it all applied, you simply lift the entire component off the board or out of the hole.
It is truly amazing stuff & I can see they now have a ROHS compliant version.
a small amount is about $20 & for a tube of the stuff is over $100, but will last for ever if you're stingy with it. glen Mars Amp Repair

[drewl]

Guess I'm spoiled.
at work we have kick ass Pace stations that cost well over $600.
having to work on state of the art crap, to clean holes, put regular iron on one side of board, and suck solder with desoldering tool, or Soldapullit on other side of hole.
assaulting both sides of hole provides maximum relief.

[Enzo]

I've been using chip quick for the occasional surface mount chip, instead of investing in more solder gear. It works pretty well, I agree. I have through hole covered, so have never tried it there.

[dai h.]

hi guys, thx for the additional tips. Update on my progress. I started on my brother's mobo with the Hakko Presto plus rubber bulb and wick, and things went well until I had about 4 spots cleared and the other 3 one hole on ea. side. Tried to wick one hole where I had a miniscule amount of solder remaining then it went downhill from there and I had a lot of difficulty. Then after googling again, went out and bought a Portasol (butane-powered thing sold under the "goot"/Taiyo Elec. co. brand but figured out this was the same one Weller was selling) based on some dude's recommendation (won contests, he was in the navy, done some difficult mods on mobos, etc.), then eventually went back to the Hakko Presto using the same screwdriver tip and was able to wick out the remaining holes mostly working one side, then the other with the wick. Wrote down some things I could think of notice to try to figure out what I was doing wrong and right after I finished this morning as follows:
--------------------------------------------------------
higher AC for Hakko Presto
raised from 100VAC to 105AC with Variac (at end measured 111VAC)
-moved iron further away from fan (was too cold before?)

-low amount of water in sponge
-new sponge

-cleaned iron tip (inside), iron pipes with lighter fluid (naptha), secured tip well with wrench

better technique
-quick wiping
-adding tiny bit of solder before soldering and then moving to joint quickly
-touch iron solder to joint solder, confirm meld/melt, then wick or add solder (when making a joint)

-used 60/40 exclusively when wicking, used silver when soldering in caps, not good to mix with eutectic??

-hardly used the Hakko Presto's boost switch

-with Portasol, the long unused sponge seemed to add a lot of oxidation to tip making tinning very troublesome (dust contributing to massive oxidation?), tinned better when cleaned on new sponge
---------------------------------------------------------

so I guess it was combination of things giving me the difficulty, being out of practice, temperature being wrong (maybe AC was too low and my DVM is reading a bit off), old sponge was contributing to tip oxidation (hmm.. I guess the soldering wasn't melding to the tip when I tried to tin it as I recall--now that I think about it), my homemade fume extractor fan was maybe too close contributing to keeping the temp. too low. When I was removing the two biggest caps (6.3V 4700uF) it took uncomfotably long (maybe 20secs?) for the solder to get hot enough to melt and start moving (I think it's all the mass from the power/ground plane plus the cap itself sinking away all the heat). Oh yeah, my brother's Linux box works. I thought I would be cool and post from there but I forgot my password... I'm going to try adding some caps to this PC's mobo again to make sure I've got things down. Thanks again dooodes!

[dai h.]

update:

I think I've figured out an easy workable method using no special equipment to remove caps. Long story short:

-used the Hakko Presto iron (with screwdriver tip), boost function on (press a button on the iron and gives a boost to 130W with max. time of 30secs.)

-solder laid across the two pads of the cap about to be unsoldered. Solder is "sandwiched" by the two pads and iron

-iron tip moved in and contacts the solder then the two solder pads contacting both capacitor leads

-desoldering happens within a "normal" timeframe of 2 to 3 secs. max. (Cap is very easily pulled out with a minimum of effort. "Like buttah". )

what I think I did different:

-counted out the 30 secs. using a clock "tick" (may have gotten panicky before releasing the boost button too fast) and provided adequate heat

-provided an immediate source of flux right at the joints (of the cap to be de-soldered) (Tinning the tip when at very high temp. causes flux to evaporate so quickly there isn't any left by the time you move the iron tip to the solder pads, and no flux = no flow.)

-contacted both leads of the cap to be desoldered (probably when contacting one side only previously, the other side of the cap and solder pad/plane connected kept sinking away heat reducing max. temp.) (I think finding/using a screwdriver tip that spans both leads of the cap to be de-soldered is key. The screwdriver tip I used for the Presto is 3.5mm wide which was barely adequate for the 6.3V1500uF caps which were de-soldered. I did not try de-soldering the three nearby which had wider spacing than the tip could reach.)

I changed mobos to a very slightly upmarket model and when I looked at this one I had worked on I saw that one of the original 6.3V 1500uFs had popped up from the PCB (probably aided by my excessive use of heat), so I had that mobo out for a while and I was thinking on and off of how to do the whole thing better (cheaper easier than using something like the equipment shown here:

http://image.blog.livedoor.jp/gahaku...6/96101193.jpg

This is from a site of a guy who solders for a living professionally. Look at the equipment in the bottom two pics ("localized flow soldering machine"? something like that). So cheaper than having to buy that. (The top pic shows where his client tried to DIY and desolder some caps himself and failed leaving the cap leads still on the board.) Good site (although all in japanese) and I think that was where I got the "sandwiching" idea.)

Unsoldered all of the 6.3V 1500uF (six?) to make sure this was a good repeatable method. I am out of practice so this will probably go easier for someone with experience and in constant practice. As for clearing the holes, I was able to do it both with de-soldering wick (3.5mm wide) and the rubber bulb within "normal" time ranges (around 3 secs. max.) although this was technically more difficult (but also from being out of practice). Anyway if someone tries this and is successful I'd be interested in knowing this is a method that can be repeated.

[bob p]

tTook Mike's advice to get some practice, and last night tried soldering/de-soldering on a PCB I had damaged when I started out DIYing. It was the board from a ...

practicing is always a good idea. i recently practiced desoldering on a 20-year old TV that gave out, and before i dragged it to the street, i decided to do a little desoldering just for the fun of it.

now here's the funny part -- being the tinkerer that i am, i diagnosed the problem, fixed it, and then only AFTER the TV was fixed, i decided that i'd rather have a new TV. so i decided to use the old TV for practice.

like some of the other guys here, i'm a bit of a minimalist when it comes to desoldering. although i have a fancy, custom-build high-flow fume hood, i don't own a de-soldering station. i still like to use a basic 40W to 60W iron and a teflon-tipped bulb.

Rob, interesting comments about forming your own tips. I've got some irons that are older than I am and tips are hard to find, so ll have to give that a shot.

Mike, nice tip about tinning and hanging the iron upside-down to cool. I discovered that by accident.

[dai h.]

hey bob...

just a couple things I wanted to add...

-remove the plastic heatsink mounter/holder thing (it's easier to access the solder joints--should've done that before--doh!!!)

-might want to use masking tape in between the two cap lead solder pads when using the screwdriver tip to reduce the chance of discoloration on the board (if that matters)

-(I don't know if these are specifically intended for removing capacitors in the manner described above, but) I saw some interesting looking soldering iron tips:

http://www.hakko.com/english/product...33.html#option

(check out tip "900M-T-R" and "900M-T-RT". Tips with a shape like that (fork?) could be perfect.)