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"Yoyo" Power Supply Repair

Volume Number: 20 (2004)
Issue Number: 5
Column Tag: Programming

"Yoyo" Power Supply Repair

by the MacTech Magazine Editorial Staff

How one goes about writing for the magazine

Problem

Apple's award-winning industrial design is world-renowned. One of the most eye-catching devices introduced with the original iBook was the so-called "Yo-yo" power adapter. Sleek and compact, it unfortunately came with a flaw; the vulnerability of the cable near where it connects to the computer. After repeated flexing (from 6 months to over a year) the braided ground portion becomes frayed and detaches inside the clear insulation. This leads to intermittent connections, then complete failure. We have experienced four of these failures, on my wife's iBook/300 and my Pismo/400. The first one was replaced under AppleCare, but the rest would require replacement at $65 each. (Used ones on eBay might be found for $35-$50).

After several months of being out-of-work (common these days for a high-tech software professional in Silicon Valley) and sharing our one functional unit between the two laptops, I finally took a look at the two broken ones we had left and decided to do a little surgery. What could go wrong? The result, after about 1.5-2 hours of careful work, is a functioning power adaptor. It's not pretty, but it should function for a while. I'd like to share the repair process.

Required Tools

Soldering iron and solder (electronic/rosin core); several pliers (slip-joint and needle-nose); an X-acto hobby knife with pointed blade; RTV silicon sealant; electrical tape and shrink-fit tubing; very steady hands and a keen eye doing close-up work. (I once worked as a professional jeweler, and have had much experience doing electrical work. YMMV..). One additional tool is a "third-hand," (http://store.yahoo.com/internettrains/exhotoexha.html) a hobby/craft device with clips to hold your work while you solder.

Disassembly

The first stage is disassembling your adaptor. You need to first cut away the clear covering on the connector; carefully cut lengthwise along the top side (away from the nub that fastens the cable end to the housing). Then cut around the connector so you can separate this piece into two sections; one will slip off the end of the connector, the other will slide back along the cable away from the end. Put these pieces aside so that they may be reassembled later. (Figure 1)


Figure 1. Initial stage of disassembly

(I apologize for not showing earlier stages of the disassembly; the idea to write the article occurred at this stage of the project).

Connector Surgery

Once you have the covering off, you will find a metal slug through which the cable threads. Pull this back to expose the tail end of the connector shell itself. Before disassembling the shell, you will need to de-solder the grounding resistor (Figure 2).


Figure 2. De-solder resistor from connector end before pulling apart

Now that you have the resistor de-soldered, bend the lead back carefully so that the connector end may be detached from the connector itself. A slight tap may be needed to separate the parts. Now the area where most of the work happens is exposed. (Figure 3).


Figure 3. Connector innards exposed.

Here you will need to cut away all the clear "potting" material so that the wires may be de-soldered from the connector. Carefully cutting into the material with your X-acto knife, you may chip the material free from the connector while taking care to NOT slice into the resistor. This one piece needs to be intact when re-assembling your power-supply cable.

After you have cleaned out all the potting material (Figure 4), you will be able to de-solder the wires from the old (broken) end of the cable.


Figure 4. Connector innards un-potted.

Here is where the "third-hand" becomes a valued tool; you need to hold the soldering iron in one hand, have a tool in another hand to pull the wire free (tweezers or a metal pointed tool) and be able to hold the work being de-soldered so that you don't get burned.

Reassembly

Now that you have removed the old wire from the connector, we can deal with the broken end of the cable to be reused. Before going further, you will have to thread back onto the cable the external parts of the assembly that were initially cut free. (You did cut them free carefully so they could be reused, and did not throw them out, right?) Make sure they go back in the order shown in Figure 5. (Additional note: one piece in the illustration did not belong; I had to remove it later. It is the piece with the "nub" that holds the cable end to the housing you wind the cord into). At this time you should also thread onto the cable a 1.5-inch segment of shrink-tubing which will later be used to protect the braided ground shielding.


Figure 5. Re-assembling the shell begins...

Now that you have threaded those parts onto the cable, you need to prepare the end for re-soldering. Cut the end clean where the cable had gotten frayed, then strip back about two inches of the outside insulation. Carefully push about an inch of the braided ground layer back from the end, and twist it off to the side (Figure 6). Twist up about 1/2 inch of the braiding and lightly "tin" the end with solder (this will help to attach it to the connector). Twist up 1/4 inch of the inner conductor and "tin" the end.


Figure 6. Preparing the end for soldering.

Now you should slip a 1/2-inch section of shrink-tubing over the inner conductor; then you are ready to attach the end to the forward-section of the connector, where it was attached before (Figure 7).


Figure 7. Reattach center conductor.

The tricky bit comes next. You will need to solder both the braided ground and one end of the resistor to the middle segment. (My apologies for not including a photo of this step).

Now that the ends are connected, you may begin to reassemble the shell. Slip the long tube over the end of the connector innards; there is one "right" way it goes on. You will see evenly spaced rectangular indentations on the end where the tip protrudes. And the tip should protrude about 1/8 inch beyond the end of the tube (Figure 8).


Figure 8. Assemble connector.

Before you fit the inner end of the inside portion over the end tube, you will be repotting the soldered area with silicon seal (Figure 9). You should also take care that the tail of the resistor is threaded out the end of the cap back toward the cable; you will need to solder it onto the outside of the shell after reassembly.


Figure 9. Example of RTV (Room Temperature Vulcanizing) silicon seal

Squeeze a small amount into the end of the tube and a little into the inner cap; then using a flat tool, pack the material into both ends of the connector. Slip the cap onto the tube and carefully, while holding the tube end with pliers, press-fit the cap onto the tube (Figure 10). You will see some of the sealant ooze out; this can be cleaned off later.


Figure 10. Press-fit cap onto tube after packing with silicon seal.

Let this assembly cure for a while, and get a cup of coffee. After it has cured, carefully bend the tail of the resistor back over the metal tip and solder it to the shell. (Refer to Figure 2).

Now you can slip the gray metal piece onto the end of the connector, and then slip the outer plastic section over the metal slug. Now slide the portion of the cover with the nub over the end of the connector, as shown in Figure 11.


Figure 11. Reassembly of outer cover.

When the segments of the shell covering are pressed together, you can complete the repair by wrapping in electrical tape. Start at the very end and work toward the cable. Keep the tape tight as you go, as the tape will be a structural member of the assembly; it will serve to keep the shell together and provide shielding to the exposed section of braided ground.

Testing

Now that you have completed reassembly, the moment of reckoning is at hand. Plug your power cord into the yoyo housing, and then into the wall socket. Now attach the repaired cable connector to your iBook or PowerBook. If your laptop is powered on and booted up, you should see the battery/power indicator showing it is charging/plugged in. Congratulations! You're an electronics repair technician!

The author of this article has been working with computers for far longer than he would like to admit, and on Macs since late 1984. His wife, two grown children, both parents, and both (older & younger) sisters are all Mac owners as well. When NOT working or playing with their Macs, Mark and his wife enjoy the company of three Yorkshire Terriers, three cats, and five cockatiels. You can reach him at n_mark_jaffe@yahoo.com.

 
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