Jump to content

Switch and Potentiometer Repair

From RetroTechCollection
Potioffen
A small rotary potentiometer opened, with German labels. Top: the ceramic substrate (Substrat) carrying the black resistive track (Widerstandsbahn) and the inner collector ring, with the three terminals (Anschlüsse) E, S and A. Bottom: the shaft (Welle) and the multi-finger wiper (Schleifer), which joins the collector ring to the track. Photo: Ulfbastel, public domain, via Wikimedia Commons.

Switch and potentiometer repair covers the moving contacts in retro computers, consoles and controllers: slide and rocker switches, momentary push switches and microswitches, rubber key pads with carbon contacts, and the potentiometers in paddles and analogue joysticks. All of them work by one metal or carbon surface sliding or pressing on another, and the faults the sources describe are much the same for all of them: dirt, oxidation, worn contact material, contacts that no longer press hard enough, and broken plastic.[1][2][3] A potentiometer is a three-terminal resistor whose sliding or rotating contact, the wiper, moves along a resistive track; with age the contact between wiper and track becomes intermittent as it moves.[4] The repair goes in three stages, cheapest first: exercise and clean the part where it sits, open it and clean and re-tension the contacts, and replace it.[3]

When to use it

[edit | edit source]

Suspect a switch or potentiometer when:

  • A machine stays dead, or needs several tries at the power switch, with a supply that measures correctly. Ruben Schade's Commodore 128 read 5.23 V at C99, before the power switch, and 0.38 V at C107 after it; the switch was clogged with dust.[5] Dave Farquhar finds that a dirty or oxidised power switch can also make an Atari 2600 power up but behave erratically.[1]
  • A reset button resets the machine by itself. Nintendo told its servicers that one type of NES power and reset switch wears in normal use and can reset the console during play.[6]
  • A console switch does nothing in one or both positions.[3]
  • A mouse button clicks erratically. Larry Pina found the microswitches in early Macintosh mice go intermittent with dust and hard use.[2]
  • The object on screen jitters as a paddle or joystick moves. Vintage Gaming and More describes jittery Atari paddles cured by cleaning the pot inside.[7]
  • Controller buttons need hard presses or work only sometimes.[8]

Measure before taking anything apart. A switch that tests good leaves the fault elsewhere, and the worked examples below show where each machine's checks go next. See also Continuity Testing and Signal Tracing.

Safety

[edit | edit source]
  • Unplug the machine before cleaning or measuring a switch. Schade unplugged his Commodore 128 from the mains before looking into its power switch.[5]
  • Let cleaner dry before power goes back on: Farquhar waits 30 minutes and Schade waited an hour.[1][5]
  • CAIG's 5% DeoxIT sprays (D5S-6, G5S-6, S5S-6 and F5S-H6) use flammable solvents.[9] Read the safety data sheet of whatever cleaner or compound you use; Chemtronics asks for this before its keypad repair kit is mixed.[10]
  • Keep track of small springs. Vintage Gaming and More warns that the spring in a momentary switch makes it hard to reassemble.[3]

Tools and materials

[edit | edit source]
  • A multimeter for continuity and resistance.[3][2]
  • A contact cleaner suited to the contact material (table below), or isopropyl alcohol and cotton buds.[3][11]
  • A small can of compressed air.[5]
  • Needle-nose pliers and a small flat-blade screwdriver for opening switch and pot cases.[3]
  • A soldering iron and a desoldering tool for parts that have to come out. See Through-Hole Desoldering.[3]
  • For worn carbon pads on rubber keys, a conductive keypad repair compound such as Chemtronics CW2605.[10]
Choosing a cleaner
Contact What the sources use
Metal contacts: slide, rocker and push switches A metal contact cleaner such as CAIG DeoxIT D-Series; Farquhar uses CRC QD contact cleaner, and Vintage Gaming and More electronics cleaner or isopropyl alcohol[9][3][1]
Carbon tracks and conductive plastic: potentiometers and faders CAIG DeoxIT Fader: F5 (with a flushing solvent) to remove dirt, F100 (no solvent) for lubrication only; Vintage Gaming and More cleans paddle pots with isopropyl alcohol[11][7]
Pots with both carbon and metal tracks or sliders CAIG DeoxIT D100S-2, its 100% spray[11]
Carbon pads on rubber keys Isopropyl alcohol or distilled water only[8]

Procedure

[edit | edit source]

Test the part

[edit | edit source]
  1. With the machine unplugged, put the meter across the switch and operate it. On an Atari 2600 slide switch the board joins four of the six pins; there should be continuity between that group and the remaining pair in one position and not in the other.[3]
  2. For a push switch or microswitch, check that the reading drops to zero at once when it is pressed. Then release it very slowly: Pina's test for a worn switch is that it passes through a grey area, typically 500 to 5,000 Ω, instead of breaking cleanly to open circuit.[2]
  3. For a potentiometer, measure from the wiper to each end while turning it through its whole travel, and compare with the service manual's figures where there are any. Atari's test for the 5200 controller, for example, wants no more than 50 kΩ with the stick at one corner and at least 430 kΩ more at the opposite corner.[12]
  4. Look at the solder joints on the underside and reflow any that are cracked or loose.[3]

Clean a switch in place

[edit | edit source]

Switches with openings in the case can be cleaned on the board; fully closed ones have to come out.[3]

  1. Look into the switch with a torch, and blow out any dust with compressed air.[5]
  2. With the power off, work the switch back and forth. Farquhar works an oxidised switch about 100 times before using any cleaner.[1]
  3. Spray a little cleaner into the opening in the switch body, or wipe alcohol on both sides of the slider with a cotton bud.[3][1]
  4. Work the switch while it is wet: Schade switched his a dozen times, and Vintage Gaming and More works a switch 15 to 20 times.[5][3]
  5. Let it dry for 30 minutes to an hour before powering up.[1][5]

Vintage Gaming and More finds that cleaning in place fixes about nine switches in ten.[3]

Open and re-tension a slide switch

[edit | edit source]
Slide switch construction diagram
The parts of a slide switch: the metal case with its tabs folded under the base, the slider with its spring-strip moving contact, and the fixed contacts. Drawn for this wiki from Vintage Gaming and More's description.

This is Vintage Gaming and More's procedure for the metal-cased slide switches of the Atari 2600.[3]

  1. Desolder the switch (see Through-Hole Desoldering) and test each contact with the meter.
  2. If a two-position switch works in one direction only, it can simply be turned round and soldered back, so that its good side carries the circuit and the faulty side lands on the pins the board joins together.
  3. Otherwise bend the metal case tabs inwards with needle-nose pliers and lift the base out. Keep every part, including the spring of a momentary switch.
  4. Clean the two moving contacts and the ends of the six fixed contacts with a cotton bud and isopropyl alcohol.
  5. Bend the moving contacts slightly wider so that they press harder on the fixed contacts.
  6. Refit the contacts in the slider. In a spring-return switch, the spring rests against the closed side of the centre slot and is loaded with the metal tab on the base.
  7. Refit the base and bend the tabs back. A small screwdriver separates the two prongs of each tab before the pliers close them.
  8. Check continuity again before soldering the switch back in.

Microswitches and tactile switches

[edit | edit source]
Philips HD8823 - Crouzet microswitch 83268-3923
A microswitch with its common (C), normally closed (NC) and normally open (NO) terminals marked on the case. Photo: Raimond Spekking, CC BY-SA 4.0, via Wikimedia Commons.

The usual repair for a small sealed push switch is a new one. Pina's verdict on the Macintosh mouse microswitch is that cleaning cannot mend worn contacts or broken plastic, and that the cure is a new switch.[2] Omron's standard tactile switches are not sealed and must not be washed: the washing agent carries flux and dust inside and causes a malfunction. Omron also warns that pressing a tactile switch too hard, or off-centre, deforms the contact dome or shortens its life.[13]

  1. Note which terminals the board uses: common, normally open and normally closed on a microswitch. On the Macintosh M0100 mouse only two of the three tabs are wired, and the switch is normally open.[2]
  2. Find an electrical and mechanical match. Pina lists switches that work electrically in the Macintosh mouse, but a solder-tab type must have its lever removed and its tabs trimmed to the width and height of the original: tabs that are too wide damage the board traces, and too tall a switch holds the button down once the mouse is closed.[2]
  3. Desolder the old switch and solder in the new one. For Omron's tactile switches the limit is 350 °C at the iron tip for no more than 3 s per joint, and no more than two soldering operations, five minutes apart.[13]
  4. Repeat the slow-release test on the new switch.[2]

Rubber keys with carbon pads

[edit | edit source]
  1. Clean the carbon contacts on the underside of the rubber pads with a little alcohol or distilled water on a cloth or cotton bud. Farquhar uses nothing harsher, because stronger cleaners can degrade the rubber.[8]
  2. Clean the contacts on the board very gently with a pencil eraser, then wipe them with alcohol. Do not sand them.[8]
  3. If a button still fails, rub its pad two or three times across a sheet of plain paper. This wears the pad, so Farquhar does it only when cleaning has not worked.[8]
  4. A pad whose carbon has worn away can be re-coated with a conductive compound. For Chemtronics CW2605: pour Part B into Part A and stir for two minutes; clean the contact with contact cleaner; paint on as little of the mixture as will cover the worn area; leave it 1 hour to become tack-free and 24 hours before use, with full cure at 72 hours at 25 °C. It can be dried faster at about 90 °C for 10 minutes, but not above 100 °C. The mixed compound stays usable for 72 hours.[10]

Nintendo's own instruction for Super NES controller contacts was not to try to clean or repair them but to replace them.[14] Fitting new pads is the fallback when cleaning fails.

Clean a potentiometer

[edit | edit source]
Potenziometer offen
A dual slide potentiometer opened: the two carbon tracks on their board (bottom) and the metal housing with the wiper contacts (top). Photo: Christiankral, CC BY 4.0, via Wikimedia Commons.

A cleaner can be sprayed in through the openings of a pot, but the thorough method is to open it. Use a cleaner made for carbon tracks: CAIG makes its DeoxIT Fader range for carbon and conductive plastic and its D-Series for metal, and recommends its 100% solution (D100S-2) for pots that have both carbon and metal tracks or sliders.[11][9] Vintage Gaming and More cleans Atari paddle pots with rubbing alcohol:[7]

  1. Take the pot out of its housing, keeping the knob, nut and any locating tab.
  2. Bend up the metal tabs that hold the pot together (four on the Atari paddle pot) and separate the halves.
  3. Clean the metal ring on the shaft part and the black resistive ring with alcohol on an old toothbrush or a cotton bud, gently, so as not to bend the wiper fingers. Leave no cotton fibres on the wiper.
  4. Bend the wiper fingers up very slightly so that they press firmly on the track.
  5. Reassemble the pot with the opening in its metal base lined up with the wires, and check that it turns through its full range before bending the tabs back down.
  6. Test it in the machine before closing the case. If it still jitters, clean it again.

Replace a potentiometer

[edit | edit source]
  1. Match the resistance and the taper. The Atari paddle pot is 1 MΩ linear; Vintage Gaming and More notes that a 500 kΩ pot also works and makes the paddle more responsive, because games use only part of the travel.[15] Taper letters are not standardised: pots made in Asia and the United States are usually marked B for linear and A for logarithmic, but some makers, particularly in Europe, mark linear as A.[4]
  2. Match the mechanics as far as possible: shaft length and shape, body size and bushing thread. Vintage Gaming and More's replacement paddle pot needed its shaft cut and the paddle knob and case ground to fit.[15]
  3. Where the pot is driven by a mechanism, set its position before fitting the linkage. Atari's procedure for the 5200 controller turns the wiper shaft until terminals 2 and 3 read 5 to 20 kΩ before the arm goes back on, and requires this alignment whenever a pot is replaced.[12]

Checking the repair

[edit | edit source]
  • Measure the switch again in every position: continuity where it should close, open circuit where it should not.[3]
  • For a push switch or microswitch, repeat Pina's slow-release test.[2]
  • For a potentiometer, repeat the manufacturer's readings where there are any, and check that it turns through its full range.[12][7]
  • Test the part in the machine before the case is closed.[7]

Common mistakes

[edit | edit source]
  • Using the wrong cleaner for the contact material. CAIG counts using a product on the wrong material as misapplication: its D-Series, Gold and Shield are made for metal surfaces, and its Fader series for conductive plastic and carbon.[9]
  • Spraying a 5% solvent-based cleaner onto aged plastic without testing it first. CAIG advises a test on sensitive parts, and the 100% solutions on parts that may be degraded.[9]
  • Greasing switch contacts with silicone grease or oil. Omron warns that silicone near switch contacts can cause contact failure.[16][13]
  • Washing or flooding an unsealed tactile switch.[13]
  • Sanding carbon contacts on a controller board, or using harsh cleaners on rubber pads.[8]
  • Leaving cotton fibres on a pot's wiper.[7]
  • Fitting a replacement switch that stands taller than the original, so that the button is held down when the case is closed.[2]
  • Losing the return spring of a momentary switch.[3]
  • Cleaning a contact that has already worn through. CAIG notes that when vintage contact material is decayed, any cleaner can make it flake off, and the part then has to be replaced.[9]

Worked examples on this wiki

[edit | edit source]
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Dave Farquhar, "Atari 2600 won't turn on? Try this.", The Silicon Underground, 26 June 2019, updated 19 January 2025 (retrieved 2026-10-25): a dirty or oxidised power switch; working it about 100 times with the power off; CRC QD contact cleaner, which he chooses as plastic-safe and quick-drying, sprayed into the side opening or the top of the switch; worked in, then 30 minutes' drying.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 Larry Pina, Macintosh Repair & Upgrade Secrets (Hayden Books, 1990), ISBN 0-672-48452-8, pp. 223 and 229-231: the SPDT microswitch under the M0100 mouse button; testing it with a meter, including the slow-release test and its grey area of 500 to 5,000 Ω; Table 12-1 of replacement switches; trimming a solder-tab switch to fit. Hosted as File:Macintosh Repair & Upgrade Secrets.pdf; see Apple Mouse Button Switch Replacement.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 Vintage Gaming and More, "Atari 2600 Switch Repair (Power and Reset/Select)", 22 July 2010, updated 4 February 2016 (retrieved 2026-10-25): tools; checking solder joints and continuity between the group of four pins and the pair; open and closed switch bodies; cleaning in place with alcohol or electronics cleaner and working the switch 15 to 20 times, which fixes about nine in ten; desoldering, testing each contact and turning a one-way switch round; bending the case tabs, cleaning the contacts and prong ends, widening the moving contacts; refitting the return spring of a momentary switch; Best Electronics as a source of new switches.
  4. ↑ 4.0 4.1 Wikipedia, "Potentiometer" (retrieved 2026-10-25): definition, the wiper, track materials (graphite, carbon particles in plastic, cermet, resistance wire, conductive plastic), taper letter codes, and the "Failure" section: ageing causes intermittent contact between track and wiper as it is rotated.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Ruben Schade, "Fixing my unbootable Commodore 128", 21 February 2021 (retrieved 2026-10-25): 0.38 V at C107 and 5.23 V at C99, the voltage dropping further after the switch was flicked, a clump of fluff seen inside the switch with a torch, compressed air, a small amount of contact cleaner worked in by switching a dozen times, an hour's drying, and GGLabs replacement switches.
  6. ↑ Nintendo of America, Service Department Bulletin #90354, "Control Deck Repair: Power/Reset Switch (Part No. 25) Enhancement", one page, undated. Hosted as File:Nintendo Service Bulletin 90354 NES Power Reset Switch.pdf; see Nintendo Entertainment System Power and Reset Switch Replacement.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Vintage Gaming and More, "Atari Paddle Repair (Cleaning Jittery Paddles)", 21 July 2010, updated 5 June 2015 (retrieved 2026-10-25): bending up the four tabs to open the pot; cleaning the metal ring on the shaft part and the black ring with rubbing alcohol on an old toothbrush or cotton bud; not leaving cotton on the six small prongs; bending the wiper tabs up slightly; reassembly and checking the full range of rotation; testing before closing the case.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Dave Farquhar, "Fix NES controllers yourself", The Silicon Underground, updated 22 January 2025 (retrieved 2026-10-25): cleaning the board contacts very gently with a pencil eraser and then alcohol, and not sanding them; cleaning the carbon contacts of the rubber pads with alcohol or distilled water and nothing harsher; rubbing a pad two or three times across plain paper only if a button still fails.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 CAIG Laboratories, "DeoxIT cracking plastics: Fact or Fiction?" (retrieved 2026-10-25): causes of cracked plastics (misapplication, degraded vintage parts, poor parts, solvent compatibility); D-Series, Gold and Shield are for metal surfaces and Fader F-Series for conductive plastic faders and carbon-based potentiometers and controls; on decayed parts any cleaner can make the contact material flake off, so use the 100% solutions or replace the part; the 5% sprays D5S-6, G5S-6, S5S-6 and F5S-H6 use flammable solvents; test on sensitive parts first; not for varnishes, semi-cured plastics or motor windings.
  10. ↑ 10.0 10.1 10.2 Chemtronics, CircuitWorks Rubber Keypad Repair Kit, technical data sheet TDS # CW2605, rev. F (09/07), via Farnell (retrieved 2026-10-25): silver/carbon/rubber coating for worn carbon contacts; 72-hour pot life at room temperature and relative humidity below 65%; tack-free in 1 hour, return to service in 24 hours and complete cure in 72 hours at 25 °C; faster drying at about 90 °C for 10 minutes, not above 100 °C; mixing Part B into Part A and stirring for two minutes; cleaning the contacts with contact cleaner and using the least material possible; testing compatibility on a non-critical area; repairs tested to over 500,000 simulated keystrokes.
  11. ↑ 11.0 11.1 11.2 11.3 CAIG Laboratories, "Best product to use for Carbon Pots and also Carbon Pots with Metal Parts?", question 18386, answered 18 April 2020 (retrieved 2026-10-25): DeoxIT Fader for carbon-based faders and controls; F5S-H6 includes a flushing solvent for dust, dirt, smoke residue and spilled drinks; F100S-L2 has no solvent and is for lubrication only; Fader Grease for more feel; D100S-2 for faders with both carbon and metal tracks or sliders.
  12. ↑ 12.0 12.1 12.2 Atari, CX5200 Field Service Manual FD100127 Rev. 4, "Controller testing without a 5200 console", p. 6-5, and "Pot arm alignment procedure", pp. 6-8 and 6-9. See Atari 5200 Controller Flex Circuit and Potentiometer Repair.
  13. ↑ 13.0 13.1 13.2 13.3 Omron, Tactile Switch Safety Precautions, Cat. No. A205-E1-07, 2025, via components.omron.com (retrieved 2026-10-25): excessive force deforms the contact dome; off-centre or angled pressing shortens life; unsealed switches in dusty places suffer contact failure; silicone in the atmosphere can stop the contacts working; manual soldering at 350 °C maximum at the iron tip for 3 s maximum on a 1.6 mm single-sided board; no more than two soldering operations, five minutes apart; standard (unsealed) switches such as the B3F cannot be washed, because the washing agent carries flux and dust inside.
  14. ↑ Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, controller diagnostic table (section 4, PDF page 52): "do not try to repair or clean the contacts: they must be replaced". See Super Nintendo Entertainment System Controller Repair.
  15. ↑ 15.0 15.1 Vintage Gaming and More, "Atari Paddle Repair (Pot Replacement)", 28 June 2010, updated 5 June 2015 (retrieved 2026-10-25): a 1 MΩ linear-taper pot (Radio Shack 271-211); cutting its shaft to fit and grinding the knob and the case; keeping the old nut to use as a washer; gluing the knob; a 500 kΩ pot as an alternative.
  16. ↑ Omron Electronic Components, "What are countermeasures to silicone for a basic switch?", FAQ FAQE20043E, updated 1 October 2021 (retrieved 2026-10-25): silicon dioxide forms on the contacts when gas from silicone materials meets the arc heat of switching, causing contact failure; sources include silicone oil and grease, silicone adhesives, coatings, rubber and wire.
Retrieved from "https://retrotechwiki.com/index.php?title=Switch_and_Potentiometer_Repair&oldid=30995"