Un-bustin' (monitor) caps with a soldering gat


— 11:19 PM on July 28, 2011

There comes a point in every computer guy's day when the phone rings, and a distraught acquaintance begins reciting error messages or describing some symptom of failure plaguing their Solitaire machine. Not too long ago, these calls were a welcome distraction. Perhaps they provided some validation of the countless hours spent peering into cathode ray tubes and liquid crystal matrices. Perhaps they were merely a common thread, facilitating rare interaction with other human beings. Whatever the reason, these tech support calls used to be a source of entertainment and pride.

Fast-forward a few years, and I've begun washing my hands of these support requests with canned responses like, "Google it," "take it to a 'Genius,'" or "that sucks, man." Somewhere along the way, dialog boxes proclaiming missing DLL files, blue screens of death, and endless pop-up ads selling virus scans just got a bit boring. Once in a great while, however, these phone calls involve something a little more obscure: something hardware-related warranting a road trip to acquire new soldering gear. I was fortunate enough to receive one of these fun calls about a Samsung 216BW LCD monitor the other day. The problem? "It don't work."

After coaxing slightly-more-precise information out of the owner, some quality time on Google revealed a recurring theme of leaky and bursting capacitors on that particular model—a relatively easy fix. Cue the A-Team theme music. Soldering equipment, screwdrivers, safety glasses, Bawls, a multimeter, and replacement capacitors were all tossed on the work bench. The A-Team theme faded into Gonna Make You Sweat at a neighbor-enraging volume, the soldering iron was plugged in and heating up, and I was good to go.

Often, the most time consuming element of such a project is disassembling and reassembling the device without breaking or losing parts. While a monitor isn't as intricate or as full of tiny screws and parts as, say, a laptop, it's still worth jotting down where each screw came from on some scratch paper. This practice is even more important when the screws are of different sizes and threading. During disassembly, I like to use a digital camera or cell phone to snap some quick pictures before removing each component. This creates a digital breadcrumb trail that can be retraced when it comes time to put Humpty Dumpty back together again.

Once the monitor's guts have been torn asunder, the misbehaving capacitors can be appropriately dealt with. Spotting a dead or dying electrolytic capacitor is usually pretty easy. They tend to bulge at the top, leak, or in extreme cases, explode. Modern electronic devices are starting to incorporate solid capacitors into their designs; those capacitors have a much higher life span and shouldn't leak or bulge. Catastrophic explosion and fire are still in the cards, though, which makes my inner pyro quite happy.

When messing with capacitors—especially the larger ones found in CRT monitors—you need to be extremely careful to ensure that they have been fully discharged. Even if the device has been unplugged for days, these tiny tin cans might still pack enough punch to make the day pretty exciting after first contact with your tender digits. A quick check with a multimeter can determine if a capacitor is hiding some leftover voltage behind its back. Should there be some contraband juice stashed away, capacitors can be discharged by either shorting the leads with a something conductive like a screwdriver (not recommended) or by attaching some insulated wires to a bleeder resistor or a standard 60-100W light bulb until the voltage drops to a safe level. Non-conductive gloves would be a handy companion during this process.

Some claim that removing the power cord and pushing the power button several times will also discharge the capacitors. This is not always true. If it makes you feel better about things, then keep on pushing that button by all means, but check the caps with a multimeter before going hands-on. These days, many electronic devices that use capacitors also wire up a small bleeder resistor in parallel. This configuration is designed to gradually drain residual stored energy over time, but unless you know with certainty that the capacitors you'll be handling have this feature, whip out the multimeter just to be safe.

Once the sparks have flown, all capacitors have been drained, and the pets have come out of hiding, it's safe to remove the dead weight. The quick and dirty method is to simply yank the bad caps off with pliers, clip any remaining wire, and punch out the solder points with a sharp solder pick. If you're in a more professional mood, remove the original solder by heating up the joint, place some desoldering wick on top of the joint, and run a hot soldering iron over the wick. The molten solder should be absorbed, allowing the capacitor to fall out cleanly once both leads have been freed from their tin restraints.

Before hastily slapping the new caps in place, take a second to ensure proper positive/negative orientation. The long lead is generally positive, and a quick glance at some neighboring capacitors will reveal any visual cues on the PCB that indicate which lead goes through which hole. Generally, the PCB will have a silk-screened circle marking indicating where the capacitor should sit. Half of that circle will be filled in or hashed, while the other half will be blank. The filled-in portion typically indicates the location of the negative lead hole.

Thread the legs through the solder point holes and flare the ends out to hold it in place while solder is being applied. If some rogue solder is preventing the lead from poking through, carefully punch out the hole using a sharp pick or needle.

Just like playing a musical instrument or quickly solving a Rubik's Cube, mastering the art of soldering requires practice, practice, practice. I don't consider myself an old soldering pro by any means, but enough electronic repair opportunities have popped up over the years that I've picked up a few handy tips along the way. The trick to a solid solder joint is preheating the receiving area a bit and applying just the right amount of solder in one smooth motion. Apply too little, and it might not stay put. Too much makes the joint brittle and prone to cracking. Overheating and remelting solder further weakens it, so getting it right on the first dab is critical. If you're not comfortable wielding a soldering gat yet, bust off a couple rounds on some scrap wire or aluminum foil before dropping molten metal on your gear.

Once you're ready to seal the deal, use the heat-and-dab technique on both capacitor leads. There may be other solder joints in the vicinity, and you need to be careful not to accidentally cross-connect them in the process. Should something go awry, this is where the desoldering wick steps in to save the day. Simply heat up the misplaced solder, apply the wick, and soak up your mistake.

With the solder applied and the capacitors held firmly in place, snip off the excess lead wires as close to the solder joints as possible, then reassemble. Tada! Good as new... hopefully.

When money is tight and the only thing holding back your hardware is a bum capacitor, DIY replacement can be an extremely economical way to go. Over the years, I've successfully saved several motherboards, video cards, and monitors from the scrap pile with simple cap replacements. The total cost of this repair including new capacitors, a new soldering iron, and desoldering wick was about $15. A new monitor could easily run you 10 times that.

Some replacement parts can be sourced from local electronic hobbyist retail stores like Radio Shack, but more often than not, they won't have the proper capacitor in stock. My personal favorite destination for capacitor shopping is Digi-Key. They stock just about every conceivable electronic component under the sun, and their prices are reasonable. You'll want to break out a ruler, since capacitors come in a wide range of heights and diameters. Also make note of the voltage and Farad (µF) ratings written on the capacitor(s) being replaced.

I'm sure this procedure is old-hat to many readers out there, but for those still earning their spurs, resurrecting a piece of kit like this is a sure-fire way to up your geek-cred. Just mind the obligatory warnings about eye protection, hot things burning other things, and electrical safety.

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