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Ribbon and Flex Cable Repair

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IDC hand press with ribbon cable and socket parts (Adafruit)
A hand IDC press, flat ribbon cable, and the body, cover and strain relief of a two-row IDC socket. Photo: Adafruit Industries, CC BY-SA 3.0.

Ribbon and flex cable repair covers the three kinds of flat interconnect found in vintage machines: round-conductor ribbon cable terminated in insulation-displacement (IDC) connectors, flexible printed cables with etched copper tracks, and the printed heat-seal or elastomeric ("zebra") connections that join a liquid-crystal display to its board. A damaged IDC cable is cut back and re-terminated with a new connector. A cracked flexible cable can sometimes be patched but is usually replaced. A heat-seal joint that has lifted can be re-bonded with controlled heat, and an elastomeric joint is cleaned and reseated.

When to use it

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Crimped wire-to-board plugs are covered in Connector Pin Replacement and Crimping, and plated card edges in Edge Connector and Cartridge Slot Cleaning.

Safety

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  • Disconnect power and batteries first. On portables, Psion's own procedure removes the main cells and the backup cell before the case is opened.[1]
  • Support LCD glass whenever it is free of its board. Psion warns that bending an LCD module can fracture it, and that liquid crystal from a broken panel must be kept out of the mouth and eyes and washed off skin with soap and water.[1]
  • An uncontrolled soldering iron runs far hotter than heat-seal film tolerates; see the temperatures below.[2][3]

Tools and materials

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  • For IDC work: a new IDC socket or header of the same pin count and pitch, an IDC press or a vice with flat jaws, a sharp blade for cutting the cable square, and a multimeter. Adafruit's instruction is to use an IDC crimper or a vice and never pliers.[4]
  • For flexible cables: a temperature-controlled iron with a fine tip, fine insulated wire, a craft knife and a magnifier; or a conductive silver pen such as Chemtronics CircuitWorks CW2200.[5][6]
  • For heat-seal joints: a temperature-controlled soldering iron.[2]
  • A replacement cable or display assembly where one can be found. Aftermarket redesigned screen cables have been made for the Psion Series 5, 5mx and 3mx.[7]

Procedure

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Re-terminating an IDC ribbon cable

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IDC-10 female connector on flat cable (02)
A 10-way IDC socket on rainbow ribbon cable, seen from the cable side. The conductors end flush with the edge of the cover. Photo: Retired electrician, CC0, via Wikimedia Commons.
  1. Note the cable's routing and orientation before removing it: which edge carries the stripe, and which way the cable leaves each connector. By convention the striped edge of a ribbon cable goes to pin 1.[8]
  2. If the cable is a PC-style floppy cable, note any twist. On IBM-compatible floppy cables the twist reverses conductors 10 to 16 for the second drive connector, and the replacement connector must go on the same side of it.[9]
  3. Cut off the damaged connector, or cut back past the damaged section, with a sharp blade at a right angle to the length of the cable. 3M's assembly instructions call for a clean cut at 90 degrees.[10]
  4. Lay the cable in the open connector so that its end is flush with the edge of the cover, the conductors sit over the contact slots, and the stripe is at the pin 1 mark.[10][4]
  5. Press the cover home squarely with an IDC press or a vice until the contacts pierce the cable and the cover latches. Do not use pliers.[10][4]
  6. Check that the cover is fully seated, parallel to the body and latched at both ends.[10]
  7. Fold the cable back over the cover and snap on the strain relief, if the connector has one.[10]
  8. Before fitting the cable, check every conductor end to end with a meter, and check neighbouring conductors for shorts. Adafruit suggests a trial build to get the orientation right.[4]

Use the cable the connector was designed for. 3M's 891 series 2.54 mm socket, for example, is made for 1.27 mm (0.050 in) pitch cable with 26 or 28 AWG stranded conductors.[11]

Repairing a cracked flexible printed cable

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Circuito impreso que conecta una pantalla a un circuito impreso rigido
A flexible printed cable joining a display to a rigid board. Photo: PedroCalamaro, CC BY-SA 4.0, via Wikimedia Commons.

Flexible cables crack where they bend. A patch across a crack in a section that flexes in use seldom lasts: David Savery's soldered patch on a Psion Series 5mx screen cable worked for about four days, and he concluded that a new cable was the only real fix.[6] Patch a flexible cable to recover data or to confirm the diagnosis, and replace it for a lasting repair.

Soldered patch:[6]

  1. Find the cracked track with a magnifier and a meter.
  2. Find solderable copper on each side of the crack, such as a pad or an exposed length of track. Savery soldered from the LCD pad to the far end of the broken track.
  3. Solder a fine wire from one exposed point to the other, using as little heat as possible. Peter Vis found the Psion Series 5 screen cable melts easily.[12]
  4. Check under the magnifier for solder splashes between neighbouring pads. Savery's first two attempts failed because tiny splashes shorted adjacent pads; he cleared them with a knife blade and confirmed with a continuity tester.[6]
  5. Secure the wire against flexing. Savery used hot glue.[6]

Conductive ink patch:

  1. Clean the surface so the ink adheres. Chemtronics specifies cleaning before applying its CW2200 pen and testing compatibility on a non-critical area first.[5]
  2. Shake the pen for 30 seconds and draw a line across the crack, bridging bare copper on each side.[5]
  3. Leave it to cure. CW2200 is tack-free in 3 to 5 minutes and conductive within 30 minutes; a 5-minute heat cure at 120 to 150 °C gives maximum conductivity, if the cable can take that heat.[5]

Re-bonding a heat-seal connector

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Heat-seal connector cross-section diagram
Layers of a heat-seal connector and where it is heated. Drawn for this wiki from Yutek Tronic's product data.

A heat-seal connector is a polyester film printed with carbon or silver traces and coated at its ends with an adhesive containing conductive particles. It is bonded to the LCD and to the board by heat and pressure. Yutek Tronic, a maker of these connectors, gives its bonding conditions as 160 to 180 °C at the connector surface for 5 to 7 seconds at a pressure of 35 to 45 kg/cm², with the heat applied only to the bonding area and both surfaces free of dust.[3]

On the original Game Boy (DMG-01), the gg8.se blog describes the established fix for dead vertical lines as dragging a hot soldering iron across the joint between the display's connector and the glass, which reflows the bond. It warns that the connector serving the horizontal lines is a different, flimsier white plastic type, easily ruined by an iron. A commenter reported success with that type at 205 °C on a temperature-controlled station, giving the bonding material's melting point as 190 °C, and warned that an uncontrolled iron above 300 °C melts the cable.[2]

  1. Identify which joint serves the missing lines: the bond to the glass or the bond to the board.
  2. Clean both surfaces of the joint if it has lifted, keeping dust out.[3]
  3. Set a temperature-controlled iron to the bottom of the ranges above, and raise it only if the bond does not take.[3][2]
  4. Press the iron along the bonded strip only, for a few seconds at a time, with even pressure. Yutek applies heat only to the bonding film.[3]
  5. Let the joint cool, then test the display before reassembly.

Elastomeric (zebra) connectors

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Zebra connector
An elastomeric connector between an LCD (top) and the pads of its board, with a centimetre scale. Photo: Caltrop, CC BY-SA 3.0, via Wikimedia Commons.

An elastomeric connector is a strip of rubber with alternating conductive and insulating layers. It joins the LCD's electrodes to the board's pads only while the frame holds it under compression; nothing is bonded.[13][14] Missing rows are cured by restoring that pressure and contact: release the display from its frame, clean the strip, the glass edge and the pads, realign them and clamp them back evenly. On the Atari Portfolio this means bending open the tabs that hold the LCD to its driver board, which work-harden after a couple of bends.[15]

Checking the repair

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  • Measure every conductor of a re-terminated ribbon cable end to end, and each pair of neighbours for shorts, before connecting it.[4]
  • Inspect IDC terminations for a fully seated cover lying parallel to the body, with the retaining latches flush.[10]
  • Inspect flex-cable patches under a magnifier for solder splashes between pads.[6]
  • Power the display and check every row and column. On a hinged portable, open and close the lid several times with the machine running.

Common mistakes

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  • Pressing an IDC connector with pliers, which closes it unevenly.[4]
  • Fitting the new connector the wrong way round, or on the wrong side of a floppy cable's twist.[8][9]
  • Cutting the cable at an angle, which leaves conductors out of their contact slots at one end.[10]
  • Using too much heat on a flexible cable or heat-seal film. Peter Vis found the Psion Series 5 cable melts easily, and the gg8.se commenter destroyed a display connector with an uncontrolled iron.[12][2]
  • Leaving solder splashes between fine-pitch pads.[6]
  • Inserting a flat cable at an angle into its socket. Psion warns this can cause short or open circuits.[1]
  • Expecting a patch in a flexing section to last.[6]

Worked examples on this wiki

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References

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  1. ↑ 1.0 1.1 1.2 Psion Computers PLC, Series 5 Service Manual, November 1997, as cited on Psion Series 5 Hinge Cable Repair: disassembly, tools and precautions (PDF pp. 17-25) and reassembly (pp. 26-27). Precautions (remove main and backup cells; earthed mat and wrist strap; do not bend the LCD module; liquid crystal from a broken panel kept out of eyes and mouth and washed off skin with soap and water), disassembly and reassembly (insert flat cables squarely into their sockets, since an angled cable can short or open circuit; keep each cable's existing bends). Hosted as File:Psion Series 5 Service Manual (November 1997).pdf; see Psion Series 5 Service Manual.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 gg8.se blog, "Why dead horizontal lines are harder to fix…", 21 July 2011 (retrieved 2026-10-25): dragging a hot iron across the connection of the DMG-01 display's connector and the glass fixes dead vertical lines; the other connector's white plastic film is easily damaged by soldering-iron heat. Comments by "Crow" (bonding material melts at 190 °C; success at 205 °C with a temperature-controlled station; irons over 300 °C destroy the cable) and others. Personal blog and reader comments.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Yutek Tronic Inc., Heat Seal Connector product data, 4 pp., hosted by Orient Display at orientdisplay.com (retrieved 2026-10-25): carbon or silver traces printed on polyester film with a bonding material containing dispersed conductive particles; conductive resistance carbon ≤40 Ω/sq, silver ≤0.2 Ω/sq; structure (polyester base film 25 or 38 µm, conductive paste 10-15 µm, conductive adhesive 10-15 µm, resist layer); bonding conditions: resin melting point 160-180 °C, sealing time 5-7 s, surface temperature at least 160 °C, pressure 35-45 kg/cm², heat applied only to the bonding film, surfaces free of dust and contamination. Manufacturer data.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Adafruit Industries, "Wiring Harnesses", in 1,500 NeoPixel LED Curtain with Raspberry Pi and Fadecandy, Adafruit Learning System (retrieved 2026-10-25), CC BY-SA 3.0: assemble IDC headers with an IDC crimper or a vice, not pliers; pin 1 of the cable is usually marked with a dark stripe; align it with the pin 1 mark on the header; make a trial build and test it with a multimeter.
  5. ↑ 5.0 5.1 5.2 5.3 Chemtronics, CircuitWorks Conductive Pen CW2200STP and CW2200MTP technical data sheet, rev. I (8/18), copy hosted by Farnell (retrieved 2026-10-25): silver-filled polymer, conductivity 0.02-0.05 ohms/sq/mil, maximum 205 °C, tack-free in 3 to 5 minutes and conductive within 30 minutes at room temperature, heat cure 5 minutes at 120 to 150 °C for maximum conductivity, flexibility "good"; clean the surface first, shake the pen for 30 seconds, test compatibility on a non-critical area; low-temperature soldering to cured traces at 177 °C for under 5 seconds.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 David Savery, "Psion Series 5MX disassembly and screen cable repair", R3UK, 6 July 2004 (cited on Psion Series 5 Hinge Cable Repair): a single conductor from an old ribbon cable soldered across a cracked track and secured with hot glue; solder splashes shorting adjacent pads; cleared with a knife blade under a magnifier; the repair lasted about four days; a new cable is the only real fix.
  7. ↑ The EPOC FAQ(ish), "Series 5mx/5/MC218 specific" (cited on Psion Series 5 Hinge Cable Repair): aftermarket redesigned cables for the 5mx, 5 and 3mx; Psion's practice of replacing the whole screen.
  8. ↑ 8.0 8.1 Wikipedia, "Ribbon cable", section "Color-coding" (retrieved 2026-10-25): one edge usually marked with a red stripe, connected by convention to pin 1.
  9. ↑ 9.0 9.1 Wikipedia, "Floppy disk drive interface" (retrieved 2026-10-25): on IBM-compatible floppy controllers a twist in the cable reverses conductors 10 to 16 for the second connector, so that two drives can share the cable without drive-select jumpers.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 3M, 3M Locator Plate 3443-82-XX: Instructions for the assembly of 3M Ribbon Cable Sockets, Series 451, 78-9101-8937-8, November 2013, copy hosted by RS (retrieved 2026-10-25): cut the cable end cleanly with a sharp blade at 90 degrees to its length; place the socket over the cable with the pin 1 indicator in the correct position; press until the contacts pierce the cable and the connector seats fully in the cover; inspect that the cover is fully seated and parallel to the body, the cable aligned with the cover, and the cover retaining devices flush; fold the cable back over the cover and snap the strain relief into place. Written for 3M's 1.27 mm series 451 sockets and 3M assembly presses.
  11. ↑ 3M, 3M IDC Ribbon Cable Socket, .100" × .100" for .050" Pitch Cable, 891 Series, TS-0449-L, 18 July 2012, copy hosted by ChipDip (retrieved 2026-10-25): wire accommodation 26 and 28 AWG stranded; phosphor bronze contacts with 0.76 µm gold in the wiping area over 1.27 µm nickel.
  12. ↑ 12.0 12.1 Peter Vis, "Psion Series 5 Screen Cable", petervis.com (cited on Psion Series 5 Hinge Cable Repair): desolder and solder the cable with as little heat as possible, because it melts easily.
  13. ↑ Wikipedia, "Elastomeric connector" (retrieved 2026-10-25): alternating conductive and insulating regions in a rubber or elastomer matrix; conductors of carbon, silver or gold.
  14. ↑ Fujipoly, "High Performance Silver Connectors" (retrieved 2026-10-25): ZEBRA connectors built of alternating parallel layers of conductive and non-conductive silicone elastomer, with a minimum of two conductive layers recommended per contact pad. Manufacturer.
  15. ↑ See Atari Portfolio LCD Missing Rows Repair, which cites Lewin Edwards' Portfolio notes as quoted on Applefritter: missing lines from the connection between the LCD and its driver board, cured by releasing and reseating the LCD; the retaining tabs work-harden after a couple of bends.
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