Jumper Wire Repair

Jumper wires on the logic board of a Seagate ST296N hard disk: fine red insulated wires run from a via and a surface-mount resistor to pins of a 74LS196, held to the board by spots of adhesive (photo: Mister rf, CC BY-SA 4.0).

A jumper wire, also called a bodge wire, is an insulated wire soldered from one point on a circuit board to another point on the same net, to restore or add a connection without following the original copper. The ends go on component leads, pads, vias or plated holes, and the wire is routed across the board and bonded down. It suits a track that is broken over a long distance, runs under a component, or passes through corroded board.

Circuit Technology Center, whose repair guide follows the numbering of IPC-7721, describes three kinds of jumper wire: those fitted during assembly, those added afterwards to change the design, and those added to correct a defect. Its procedure 6.1 sets out how to choose, route, terminate and bond them. Manufacturers fitted them too: Sega's drawings for the PAL Master System II show a jumper on the solder side from C39 to the ground of IC9, and Atari's Tech Tip 14 for the 5200 adds one to reinforce a ground track.

For a short break that can be bridged along the track itself, see PCB Trace Repair.

When to use it

• A track is open over a long run, or between points with components in the way, and its two ends are easier to reach at component legs, vias or pads than along the track.
• A via or plated hole has failed and the connection has to be made round it. Battery Explosion, Capacitor or Corrosion Damage connects the trace on each side to another point on the same net instead of relying on a corroded via; see also Via and Through-Hole Repair.
• A pad has gone and the lead has to be joined to the next point on its track; see PCB Pad Repair.
• A board area is burnt or eaten away and the circuit has to be re-routed round it; see Burnt PCB Repair.

Find the two ends on the machine's schematic, and confirm them with a meter before cutting any wire: SparkFun found its cut TX line by probing with a multimeter, and notes that on a complex board the next exposed copper on the net may only be found from the board's layout. Continuity Testing and Signal Tracing covers the measurement.

Safety

• Unplug the machine and remove any batteries. On equipment with a picture tube, follow the CRT Discharge Procedure first.
• Rosin (colophony) flux fume can cause occupational asthma. Use fume extraction while soldering.
• Wires soldered to a lifted or clipped component lead can short to neighbouring parts. Insulate them.

Tools and materials

• Insulated solid wire. Circuit Technology Center recommends solid tin-lead plated copper, 22 to 32 AWG, insulated with Kynar, Milene, Kapton or Teflon, and chooses the smallest diameter that will carry the current. It says silver-plated wire must not be used because it can corrode, and that wire with a nicked conductor should not be used.
• 30 AWG Kynar wire-wrap wire, the traditional choice for logic-level signals, is silver-plated soft copper 0.255 mm in diameter. Kynar (PVDF) melts at about 177 °C, below the 183 °C of 63/37 solder; PTFE (Teflon) melts at 327 °C.
• Solderable enamelled wire, whose polyurethane coat burns off in solder at 390 °C or more without stripping.
• Heavier wire for power and ground. Atari's Tech Tip 14 uses 16 gauge bus wire in plastic sleeving.
• Wire strippers that do not nick the conductor, flux, leaded solder and a temperature-controlled iron with a fine tip; see Through-Hole Soldering and Recommended Tools.
• Insulating sleeving for wires on lifted or clipped leads.
• An adhesive to hold the wire down: tape dots or strips, quick-set adhesive or hot-melt adhesive. Some jumper wire has a heat-set adhesive coat bonded with a special tool. One EEVblog contributor uses thick cyanoacrylate.

The resistance of the wire can matter. Copper wire of 30 AWG has about 339 mΩ per metre and 26 AWG about 134 mΩ per metre, so a 100 mm run of 30 AWG adds about 34 mΩ. Circuit Technology Center notes that the length and gauge of a jumper may be critical and says to follow the wiring list where one exists.

Procedure

Plan the route

Routing and bonding a jumper wire: lapped along a pad at one end and wrapped round a lead at the other, routed in X and Y round the IC, and bonded near each joint and bend (rules from Circuit Technology Center procedure 6.1).

1. Mark both termination points on the schematic and check them on the board with a meter.
2. Choose the termination at each end: a component lead, a pad or conductor, or a plated hole. Avoid pads and vias used as test points; a jumper must not pass over them.
3. Plan the route on the component side unless there is a reason to use the other side. The Sinclair QL RGB Port Repair runs its wire on the solder side, where Sinclair's own modification also cut tracks.
4. Route the wire in X and Y, as directly as possible with as few bends as possible.
5. Keep the route off component bodies and leads, away from heat sinks, and out of component footprints unless the layout leaves no other way.
6. Keep the wire no more than 3.2 mm above the board or any component where it could get in the way of mounting the board.
7. Where the wire must cross a land, leave enough slack that it can be moved aside when that part is replaced.

Prepare the wire

1. Measure the route and cut the wire about 12.7 mm longer.
2. Strip each end to suit its termination, without nicking the conductor.
3. Tin the stripped ends if needed and clean them.

Solder the ends

A jumper from a jumper pad to a via on the same net, with the via's mask scraped off (SparkFun, CC BY-SA 4.0).

1. Clean the termination points and scrape any coating or oxide from the pads, leads or tracks to be soldered. Remove old solder from a point if it is in the way.
2. On a pad or a track, lay the wire parallel to it, centred, without overhanging its sides, and solder it there. Circuit Technology Center does not recommend a wire soldered across a pad at right angles, or several wires overhanging one pad.
3. On a component lead, wrap the wire at least 90 degrees round the lead before soldering.
4. In a plated hole, solder the wire into the hole so that it can be seen on the other side of the board.
5. On a via, scrape the mask from the via first. SparkFun's repair of a cut trace was soldered to a tented via in this way.
6. Solder the first end and clean the joint. Keep the insulation within two wire diameters of the joint; it may touch the solder but must not be buried in it.
7. Form the wire along the planned route. Do not bend it tighter than a radius of three times the conductor diameter.
8. Solder the second end and clean the joint.
9. Insulate a wire soldered to a lifted or clipped lead.

Secure the wire

1. Bond the wire within 6 mm of each solder joint.
2. Bond it within 6 mm of each bend.
3. On straight runs, bond it at intervals of 25 mm.
4. An insulated wire shorter than 25 mm does not need bonding.

Bare wire is acceptable only for a run of less than 12.7 mm between terminations, and then only where it keeps the minimum clearance to other conductors.

Record the change

Note the jumper and its route on your copy of the board's schematic or layout. Circuit Technology Center documents each jumper's routing and any hole drilled for it on a drawing.

Checking the repair

• Measure continuity from the source pin to the destination pin through the new wire.
• Check that the wire end and its solder do not touch the neighbouring pads, leads or tracks, and measure for shorts to them.
• Check that the joints match Circuit Technology Center's acceptable forms: wire parallel to and centred on the pad, at least 90 degrees round a lead, visible on the far side of a plated hole, and insulation close to but not inside the joint.
• Check the bonds: within 6 mm of each joint and bend, and at 25 mm intervals along the run.
• Power the machine and test every function on the repaired net.

Common mistakes

• Circuit Technology Center does not allow bare jumper wire longer than 12.7 mm between terminations. Use insulated wire for anything longer.
• Circuit Technology Center rules out routing over component bodies or leads and against heat sinks; where a wire crosses a land, it leaves enough slack to move the wire aside when that part is replaced.
• Kynar insulation melts back if the iron dwells near it. An Atari XEGS memory-upgrade builder changed to Teflon-insulated wire after his kit wire melted back.
• Circuit Technology Center does not recommend a wire soldered across a pad at right angles, or several wires overhanging one pad.
• An unbonded wire is free to move at its joints. Anchor it beside each joint and along its length.
• A heavy wire can carry enough heat from the second joint to melt the first. A single strand of stranded wire does not easily do so.
• A thin wire on a power or ground path reduces the current it can carry; size the wire for the current.
• A jumper to the wrong pin. Check both ends against the schematic and with a meter before soldering.

Worked examples on this wiki

• Atari 5200 Joystick Pot Line Repair: Atari's Tech Tip 14 adds a sleeved 16 gauge bus wire from U7 pin 1 to the ground lead of C104.
• Sega Master System II Video Output Repair: Sega's factory jumper from C39 to the ground of IC9, which the guide says to check is present.
• Commodore 64 PLA Replacement: two vias damaged by a non-factory socket, repaired with jumper wires.
• Commodore 64 Voltage Regulator Replacement: a short wire from the bridge rectifier's ground pin to a ground point under the power switch, after an earlier repair damaged a via.
• Atari Jaguar Power Regulator Replacement: lifted pads at U38 rebuilt with Kynar wire to the via and to the current-sense resistor R169.
• Sinclair QL RGB Port Repair: a link from a J7 pin to the matching ZX8301 socket pin.
• Atari XEGS Mods & Upgrades: a memory upgrade wired point to point, where kit wire with poor insulation was replaced by Teflon-insulated wire.

Related pages

• PCB Trace Repair
• PCB Pad Repair
• Via and Through-Hole Repair
• Burnt PCB Repair
• Continuity Testing and Signal Tracing
• Through-Hole Soldering
• IC Removal and Socketing
• Battery Explosion, Capacitor or Corrosion Damage
• Recommended Tools