SAVING DAMAGED PRINTED CIRCUIT BOARDS (ELECTRONICS REPAIR)

HOW TO SAVE DAMAGED PRINTED CIRCUIT BOARDS (PCBs)


When you desolder a through-hole component, one unfortunate result of failing to get the hole hot enough is that its copper lining comes out with the lead. If you see what looks like a sleeve around the lead, you’ve torn out the copper. On a double-sided board, it’s not a catastrophe.

When you replace the part, be sure to solder both the top and bottom contact points, and all will be well. You might have to scrape some of the green solder mask coating off the top area to get contact between the lead and the foil. That’s best done with the tip of an X-Acto knife.

Pulling the sleeve out of a multilayer board can destroy it because you have no way to reconnect with interior foil layers that were in contact with the sleeve. If you’re lucky, that particular hole might not have had inner contacts, and soldering to the top and bottom may save the day, so it’s worth a try. Don’t be surprised, though, if the circuit no longer works.

If you can figure out where they go, broken connections can be jumped with wire. On double-sided boards, it’s not too hard to trace the lines visually, though you may have to flip the board over a few times as you follow the path. When you find where


a broken trace went, verify continuity with your DMM, from the end back to the break. Don’t forget to scrape off the solder mask where you want to contact the broken line.

Wire jumping can help save boards with bad conductive glue interconnects, too. On a double-sided board, you can scrape out the glue and run a strand of bare wire through the hole, soldering it to either side.

Forget about trying this on a multilayer board, however; you’ll probably trash it while trying to clean the hole. On those, it’s best to run an insulated wire around the board from one side to the other. That adds extra length to the conductive path, which could cause problems in some critical circuits, especially those operating at high frequencies.

At audio frequencies, it should be fine. If some interior layers are no longer making contact with the glue, this won’t work. Most conductive glue boards I’ve seen have been double-sided, making them suitable for wire jumping.

If the board is cracked from, say, having taken a fall, scrape the ends of the copper lines at the crack. It’s possible to simply solder over them, bridging the crack, but that technique tends to be less permanent than placing very fine wire over the break and soldering on either side.

To get wire fine enough, look through your stash of parts machines for some small-gauge stranded wire. Skin it, untwist it and remove a single strand.

Sometimes there are multiple broken lines too close to each other for soldering without creating shorts between them. To save boards like that, scrape the solder mask off close to the crack on every other line. Then scrape the in-between lines farther away from the crack.

 Use the bare wire strands to fix the close set, and use wire-wrap wire (very thin, single-strand, insulated wire used with wire-wrap guns for prototyping experimental circuitry) or enamel-insulated “magnet wire” to jump the farther set.

Wire-wrap wire is especially good for this kind of work because its insulation doesn’t melt very easily, so it won’t crawl up the wire when you solder close to it, exposing bare wire that could short to the repaired lines nearby. Plus, it’s thin enough to fit in pretty small spaces.

For even tighter environments, use the magnet wire. Just be sure to tin the ends of the wire to remove the enamel, so you’ll get a good connection.

It’s possible to repair broken ribbon cables in stationary applications (the ribbon doesn’t move or flex), if they are the copper-conductor type of ribbons, not the very thin, printed style. Fixing cracks with wire is a tedious, time-consuming technique, but it works. Accomplishing it without causing shorts takes practice and isn’t always possible with very small, dense boards and ribbons.

On multilayer boards, cracks and torn sleeves are extremely difficult to bypass. If you have a schematic, you may be able to find the path and jump with wire. Without one, it’s pretty much impossible when the tracks are inside the board.