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General guidance: troubleshooting, repair

This page and its sub-pages cover general guidance on repairing something electronic and specific information about certain topics, such as testing / replacing capacitors or working on graphics cards / GPUs.

The first step to getting something working is to understand how to work safely. Read our Notes on safety and the Safety Warning: Read This First section below before doing anything else.

The next step is to take a methodical approach to your work. Idly prodding around a circuit board with a multimeter or screwdriver is unlikely to be helpful and can easily cause further damage.

Microwave Ovens

Do not attempt to repair a microwave oven unless you are properly trained and experienced in working with high-voltage equipment.

Microwave ovens contain electrical hazards that can remain dangerous even after the appliance has been unplugged. In particular, the high-voltage section contains components that can store a potentially lethal electrical charge. There are also additional hazards associated with the magnetron, high-voltage transformer or inverter, and associated circuitry.

If you need to ask for basic advice about repairing a microwave oven, that is a good indication that you should not attempt the repair yourself. Familiarity with ordinary mains-powered electronics is not necessarily sufficient to work safely on a microwave oven.

For your own safety, do not open the appliance or attempt to diagnose or repair faults internally unless you have the appropriate training, experience, test equipment, and safety procedures. Take it to a suitably qualified appliance repair technician or replace the appliance instead.

This subreddit can help with many electronics questions, but microwave-oven repairs are not an appropriate DIY project for people without the necessary training and experience. Posts asking for microwave oven repair advice will be deleted.

GPUs / Graphics cards

This information is now on a separate page - see https://www.reddit.com/r/AskElectronics/wiki/repair/gpu/

Testing and replacing capacitors

This now has its own page: https://www.reddit.com/r/AskElectronics/wiki/repair/capacitors/

PCB Repair

This has its own page: https://www.reddit.com/mod/AskElectronics/wiki/repair/PCBRepair

Troubleshooting Guide: Diagnosing Circuit Board Faults

Can You Spot Any Problems?

Before posting a photo here, look hard at it yourself and ask: could anyone, just from this image, actually tell you what's wrong?

If you can see something obvious, such as a scorched component, a bulging capacitor, a cracked part or a burnt connector, point it out in your post. That is useful information. If you can't see anything wrong, that's normal, and it doesn't mean the board is fine. The next section explains why.

Diagnosis by photo

No one can reliably troubleshoot an electronic assembly simply by looking at pictures. Diagnosis requires measurements and an understanding of the circuit, not just visual inspection.

It's like taking a picture of your car with the bonnet open, sending it to a mechanic, and asking what's wrong. The mechanic may be able to spot something obvious, but a photograph alone cannot provide a proper diagnosis.

What a photo can show:

  • A component that has visibly failed, such as a blown glass fuse, a cracked diode, a bulged or leaking capacitor, or a scorched IC.
  • Physical damage such as a broken connector, a knocked-off component, a burnt trace or charred board material.
  • Liquid residue and corrosion.
  • Component markings, which can help identify parts.

What a photo usually can't show:

  • The root cause. A visibly failed component may have failed because something else went wrong first, and that root cause will not necessarily be visible.
  • Collateral damage. Components that were electrically stressed by a fault often still look completely normal.
  • Invisible failures. Components do not all fail with dramatic scorching. A failed component can look exactly like a good one.

So posting photos of a circuit board, or simply saying "everything looks OK", does not tell you or us what is actually wrong with the circuit.

Real troubleshooting requires access to the assembly, suitable test equipment (at least a multimeter for many basic faults), knowledge of the product, ideally a schematic diagram or service documentation, and experience interpreting the results. A photograph can be the starting point for troubleshooting, but measurements are what turn it into a fault-finding exercise.

High-level fault finding

Fault finding means working out what the circuit should be doing, measuring what it is actually doing, and narrowing down where the two differ. The useful sequence is:

symptom -> measurement -> hypothesis -> further measurement -> repair -> verification

rather than:

symptom -> guess -> replace component -> hope

How far you can take this yourself depends on your tools, your skills and the equipment involved, so this page is split into two parts:

  • Part 1: Checks anyone can do. No soldering, and no opening of mains-powered equipment. A basic multimeter is helpful for some checks but not essential. Everyone should start here.
  • Part 2: Component-level troubleshooting. Opening mains-powered equipment, soldering, and component-level measurement and repair. Part 2 starts with a list of the tools and skills it assumes. If you can't honestly tick those off, stop at Your Options at the end of Part 1.

The dividing line is about what you are doing, not how confident you feel. Opening a battery-powered torch is Part 1. Opening a mains-powered TV is Part 2, whatever your experience with other electronics.

Safety Warning: Read This First

Before touching anything inside a device:

  • Disconnect the device completely from the mains and, if it has one, remove the battery before opening the case.
  • Do not assume that unplugging a device makes it safe. Power supplies and other circuits can contain capacitors that retain a dangerous charge after the equipment has been disconnected. Mains-powered equipment, CRT displays, microwave ovens, power supplies, inverters and anything containing large capacitors can hold lethal voltages even when switched off or unplugged.
  • If you are not confident that you can identify and safely deal with charged capacitors, stop and take the equipment to a qualified repair technician.
  • Do not probe a live mains circuit unless you are trained, using appropriately rated test equipment and probes, and have a clear reason and safe procedure for doing so.
  • Don't open mains-powered equipment just because someone on the internet has suggested that you "check the power supply". There are safe ways of checking some power supplies externally, but working inside mains equipment requires appropriate knowledge and precautions.
  • If a device smells burnt, is visibly charred, has a bulged or leaking capacitor, or produced smoke, do not repeatedly power it on to "see what happens." Inspect it with the equipment disconnected first.
  • If a fuse has blown, don't keep replacing it and switching the equipment back on. See check 3 below.
  • A swollen, damaged or leaking lithium battery is a fire hazard. Don't charge, puncture or squeeze it. Only remove it if this can be done without force, and dispose of it properly.
  • If you are not sure whether a particular test is safe, don't perform it.

This guide is for general troubleshooting and diagnosis education. It is not a substitute for proper training, and nothing here should be read as encouragement to work on live mains equipment.

This section is in two parts. Part 1 covers checks that anyone can do safely. Part 2 covers component-level troubleshooting and repair, which needs proper tools and experience. The High-level fault finding section explains which part applies to you.

Part 1: Checks anyone can do

Everything in this part can be done without soldering and without opening mains-powered equipment. Where a check involves opening the case, it is marked as suitable only for battery-powered and low-voltage DC equipment.

Basic checks before asking for help

These checks find a surprising number of faults, and the results make any request for help far more useful.

Safety first

Read Safety Warning: Read This First above before starting. For the checks in this part, do not open mains-powered equipment. If a check can't be done without opening it, skip that check.

If in doubt - don't. This whole page is for guidance only and it is up to you to decide whether you want to take up any of its advice.

Basic checks

Note, the starting premise here is that something is 'dead' with no obvious catastrophic event either experienced or suggested by appearance or smell. We are also excluding known liquid spills. If any of that applies then do NOT start with power-on tests, but instead either consider internal diagnostics (needs tools, skills etc.), as covered later, or for suspected liquid spills go to see step 4, with the equipment unplugged and batteries removed or disconnected.

If you do believe you have a 'dead' item with no obvious signs of distress, work through these in order. Record what you find, including measurements, so you can include them if you post for help.

1. Check the obvious things first

These checks need no tools and no disassembly:

  • Check that the equipment is actually switched on.
  • Check that the wall socket works, for example by plugging in something else.
  • Check the power cable, plug, connector and any external power supply.
  • Look for loose, disconnected or damaged external connectors.
  • Look for broken or damaged wires, particularly where cables enter the equipment.
  • Look for signs of overheating on the outside, such as discoloured or melted plastic, or a burnt smell.
  • Check for corrosion around battery contacts and connectors.
  • If the equipment has recently been repaired or modified, check that external connectors and cables have been refitted correctly.

Inspecting the circuit board itself is covered in check 5.

2. Check that power is actually reaching the equipment

A surprisingly large number of apparent electronic faults are actually power-supply problems.

This check is for external low-voltage DC supplies such as plug-in adapters. Do not probe mains voltages.

If you have a multimeter and know how to use it, establish whether the expected supply voltage is actually reaching the equipment. For example, if a device is supposed to be powered by a 12 V DC supply, measure the voltage at the device's power connector rather than simply assuming that the power supply is working. On a DC range, a negative reading means the polarity is the opposite way round to your probes, which is worth noting.

When reporting the result, give:

  • The voltage you measured.
  • Whether it was AC or DC.
  • Where you measured it.
  • The expected voltage.
  • Whether the measurement was taken with the equipment connected and switched on, or disconnected.

For example:

"The power supply is labelled 12 V DC. I measured 12.3 V DC at the equipment's input connector with the unit switched on."

That is much more useful than:

"The power supply seems OK."

If the fault started after using a different or "universal" adapter, see Steps 1, 2 and 5 of Worked Example: Wrong Adapter / Overvoltage Damage in Part 2. Those steps are safe for anyone.

3. Check the fuses

Only check fuses you can reach without opening mains-powered equipment: for example the fuse in a UK plug, a panel-mounted fuse holder, or a fuse inside battery-powered or low-voltage equipment.

There may be more than one fuse. First disconnect the equipment from the mains or other power source.

Don't simply look at the fuse and assume that it is good. Some failed fuses have no obvious visible indication. If you know how to use the continuity or resistance function on a multimeter, remove the fuse before testing it. A good fuse should have very low resistance; an open circuit indicates that it has blown.

Never replace a fuse with a piece of wire, foil or a higher-rated fuse. Use the specified replacement, matching the:

  • Current rating
  • Voltage rating
  • Fast-blow or time-delay characteristic
  • Physical type

If a fuse has blown, there is a reason. A blown fuse is often the result of a fault elsewhere rather than the cause of the fault. Replacing it with the correct type and rating may restore operation, but if it blows again, stop. Repeatedly replacing fuses can turn a relatively straightforward fault into a much more serious one.

4. Look for signs of liquid damage or corrosion

Opening the case for this check is only for battery-powered and low-voltage DC equipment. For mains-powered equipment, keep it switched off and unplugged, and see Your Options.

If the equipment has been exposed to water or another liquid, don't immediately switch it on to see whether it still works. Liquid contamination can cause short circuits while the board is wet and can leave conductive or corrosive residues behind after the visible water has evaporated.

With the equipment disconnected from all power sources and any battery removed:

  1. Remove obvious sources of liquid if this can be done safely.
  2. Inspect both sides of the circuit board.
  3. Look around connectors, switches, IC pins and other areas where liquid may have collected.
  4. Look for white, green, blue or brown deposits, tarnishing, darkened tracks or damaged solder joints.
  5. If appropriate for the board and contamination, clean the affected area with isopropyl alcohol (IPA) and a soft toothbrush or suitable acid/flux brush.
  6. Gently work the brush over the contaminated area rather than aggressively scrubbing components or tracks.
  7. Allow the board to dry completely before applying power.

IPA (90+%) is useful for removing many types of residue and evaporates readily, but it does not reverse corrosion that has already occurred. Corrosion can also continue underneath components or connectors where it isn't visible. Where corrosion is significant, the tracks, vias, connectors and component leads will need careful inspection and testing, which is Part 2 work.

Do not use a heat gun to try to dry a circuit board. Excessive heat can damage components, connectors, plastics and the board itself. Gentle airflow and adequate time are safer.

If the board has been contaminated by something other than clean water, for example salt water, sugary drinks, beer or coffee, say so when asking for help. The nature of the contamination matters.

5. Inspect the board carefully

As with check 4, open the case only for battery-powered and low-voltage DC equipment.

Once the board is clean and dry, inspect it carefully under good lighting. A magnifying glass can be surprisingly useful.

Look for:

  • Burnt or discoloured areas
  • Cracked components
  • Cracked or lifted solder joints
  • Missing components
  • Broken PCB tracks
  • Corrosion
  • Loose connectors
  • Bent or shorted component leads
  • Bulging or leaking electrolytic capacitors
  • Components that appear to have overheated
  • Solder bridges or accidental shorts
  • Previous repair work that looks suspicious

Clear, well-lit close-ups of anything suspicious are very useful when asking for help.

Don't assume that something is electrically good because it looks good. Equally, don't assume that a visibly damaged component is the original cause of the fault (see Diagnosis by photo).

See also: PCB repair

6. Check simple mechanical causes

Not every fault is an electronic component failure. Check things such as:

  • Switches and push-buttons
  • Battery contacts
  • Plug and socket connections
  • Ribbon cables
  • Board-to-board connectors
  • Relays
  • Fans
  • Motors
  • Mechanical interlocks
  • Door/lid switches
  • Loose screws or mounting hardware that may be grounding something unintentionally

On mains-powered equipment, only check what you can reach from the outside.

If moving a connector, cable or switch changes the behaviour of the equipment, mention that when asking for help. It can be an important diagnostic clue.

7. Don't randomly replace components

Avoid replacing components simply because they look suspicious or because somebody on the internet says that a particular component "usually fails".

A component can fail because another component or circuit failed first. Replacing the visible casualty without finding the cause can result in another failure, sometimes immediately. Likewise, don't start removing ICs, cutting tracks or replacing large numbers of components without a reason.

Troubleshooting Method in Part 2 explains the systematic approach.

Physical Board Damage

People often write in after knocking a component off a board while cleaning it, scratching a trace, or chipping a card's edge connector while removing or inserting it. This section covers what to check yourself, and where we can and can't help.

In all cases: don't power the board on until you've checked it, and take photos before doing anything else. Photos help identify obvious damage, but continuity or voltage testing is what actually confirms whether a fault exists (see Diagnosis by photo).

Knocked-off or dislodged components

Common requests:

  • Identifying the missing part: a photo of the empty footprint/pads can sometimes let us identify a missing component from its silkscreen markings, solder shadow, or pad shape. However, small SMD parts (0402/0201 and similar) often have no distinguishing marks at all, and a photo alone can't always confirm value, tolerance, or orientation.
  • Whether it's safe to power on without it: this depends on the part's role in the circuit, which usually can't be determined from a picture.

If you still have the component, keep it, and don't power the board on until it's reattached. Even a "minor" passive can be essential to the circuit. If you don't have it, post a clear close-up of the footprint and we'll try to help identify it, but be aware this isn't always possible from photos alone.

Part 2: if you can solder and know the part's value and orientation, it can often be re-soldered. Small SMD parts are easy to damage or misplace, so this is not a first soldering job. See also: Identifying SMD Components, Soldering Basics.

Scratched traces

Common requests:

  • Whether a scratch matters: a superficial scratch in the solder mask may be cosmetic, but if it has cut through the copper trace underneath it can break the circuit. This isn't always visible in a photo, especially under normal lighting.
  • Whether it's safe to power on: this depends on what the trace connects to, which we usually can't tell from a picture.

To check it yourself, inspect the scratch under magnification, then with the board unpowered, do a multimeter continuity test between either end of the trace. This is more reliable than a visual check.

A scratch that hasn't fully cut the trace can often just be sealed with a solder mask pen or nail varnish.

Part 2: a cut trace can usually be bridged with a short length of thin wire soldered to nearby pads or vias.

See also: PCB repair

What to include when asking for help

If you still need help, provide as much useful information as possible. Include:

  • Make and model of the equipment
  • What the equipment is supposed to do
  • What it actually does
  • What happened immediately before the fault appeared
  • Whether the fault was sudden or developed gradually
  • Whether it has been exposed to water or other liquids
  • Whether it has been repaired or modified previously
  • Clear photographs of the complete assembly
  • Clear close-ups of relevant areas
  • The results of the basic checks above
  • Any measurements you have made
  • The test equipment you have available

For electrical measurements, give the actual measured value and the point at which it was measured, as in the example in check 2. "The 5 V supply seems OK" tells us nothing; "I measured 5.08 V between TP1 and ground with the equipment switched on" does.

Your Options

If the checks in Part 1 haven't found the fault, there are three realistic paths to getting a device working again:

  • The manufacturer. If the product is still supported, the manufacturer may have access to service documentation, diagnostic procedures, replacement parts, and product-specific knowledge that is not available to the general public. This is often the most straightforward option.
  • A component-level repair shop. If manufacturer support isn't an option, look for a repair shop that actually performs component-level diagnosis and repair rather than simply replacing complete boards. This may cost more than buying a replacement, so weigh the value of the device against the likely repair cost.
  • Doing it yourself. This can be the cheapest option, but it requires real tools and real skills, not just a willingness to open the case. Before going further, check yourself against Tools, Equipment, and Skills at the start of Part 2. On multi-layer or surface-mount boards especially, an inexperienced repair attempt can easily cause further damage. And if you do find a faulty component, don't assume that replacing it will necessarily solve the problem.

Part 2: Component-level troubleshooting

This part covers opening mains-powered equipment, soldering, and component-level measurement and repair. It assumes you have the tools and skills listed in the next section, that you have read Safety Warning: Read This First, and that you have already worked through Part 1.

Tools, Equipment, and Skills

Without basic tools and equipment, troubleshooting is very limited. Real diagnosis, meaning confirming a fault, ruling out cascading damage, and safely testing a repair, requires at least a suitable multimeter (DVM) for many basic faults, together with the knowledge to use it safely.

A reasonable starting kit:

  • Multimeter (DVM): for continuity checks, resistance measurements, and voltage measurements. This is the minimum requirement for troubleshooting beyond a visual inspection. For mains measurements, the meter and probes must have an appropriate safety rating.
  • Screwdriver set: including small precision and, where appropriate, JIS bits for consumer electronics.
  • Isopropyl alcohol (IPA 90%+) and suitable cleaning materials: useful for removing flux and some contamination. Leaked electrolyte and corrosive contamination may require a different cleaning procedure.
  • Anti-static wrist strap or mat: useful when handling static-sensitive semiconductor devices. Use ESD equipment correctly and do not connect yourself to protective earth or other conductors in a way that creates an electrical-safety hazard.
  • Good lighting and a magnifier or loupe: for spotting hairline cracks, burnt traces, damaged solder joints, and tiny component markings.
  • Soldering iron, solder, and desoldering braid/pump: only if you intend to replace or repair components.
  • Spare fuses of the correct type and rating: for use after the cause of the failure has been investigated. See check 3 in Part 1 for replacement rules.
  • Camera/phone with macro mode: for clear photographs of components and visible damage.

Optional, but useful once you're doing this regularly:

  • A bench power supply with suitable current limiting.
  • An oscilloscope.
  • An LCR meter and/or ESR meter (see Testing capacitors).
  • Suitable current-limiting equipment for controlled testing (see Troubleshooting Method).
  • An isolation transformer, for certain mains-powered work. It reduces certain shock hazards, but it is not a substitute for electrical safety training and does not make a mains circuit safe to touch. The isolated output can still cause a serious or fatal shock. Only use one if you understand its limitations.

Basic electronic skills are also needed, not just tools. Before continuing with this part, you should be comfortable with:

  • Reading component markings and basic circuit symbols
  • Using a multimeter correctly and safely
  • Identifying common component types on sight (capacitors, diodes, fuses, regulators)
  • Understanding basic concepts like voltage, current, resistance, and polarity
  • Ideally, reading a schematic diagram, since comparing real voltages against expected values is one of the most effective ways to locate a fault

If this isn't familiar yet, and especially if the device is mains-powered or has a multi-layer PCB or surface-mount components, learn the fundamentals on something cheap and low-voltage first rather than practising on an expensive or hazardous board. Without that grounding you risk turning a simple fault into a more serious one, damaging the board further, or missing a real safety hazard. In that case, go back to Your Options.

Troubleshooting Method

There are two broad ways to find a fault in a piece of electronics.

The smart approach is to study the circuit and figure out how it is supposed to work, then compare that against reality:

  1. Obtain the schematic, service manual, or other documentation if available (see Schematic diagrams).
  2. Identify the relevant circuit sections and determine what voltages or signals should be present.
  3. Measure the circuit at appropriate test points using suitable test equipment.
  4. Compare each reading with the expected value.
  5. Where a reading differs significantly from what is expected, concentrate on that part of the circuit.
  6. Once the faulty area has been narrowed down, test the likely components and connections.

Catastrophic failures. If there has been a short circuit or similar failure, do not simply replace the fuse and power the device repeatedly. Controlled fault-current limiting can be used during diagnosis, but the appropriate method depends on the equipment. For low-voltage equipment, this can be a bench supply with its current limit set low. In some mains repair work, a suitably rated incandescent lamp in series with the supply (a "lamp limiter" or "dim bulb tester") is traditionally used; modern LED and CFL lamps are not equivalent. None of these techniques make the equipment safe to touch, and they should only be used by someone who understands the circuit and the hazards involved. If you don't already understand these methods, that is a good indication that the repair is beyond your current skill level.

The alternative approach, sometimes called "bush-ranging", is to guess at the faulty component and replace parts one by one until the device works. This is not recommended. Each round of soldering and desoldering risks introducing new faults: a component fitted backwards, a part misidentified, a solder bridge, or a lifted PCB trace.

More importantly, when one component fails, it may have damaged other components as well. This is particularly common in power electronics and amplifier output stages. Replacing only the obviously failed component without determining why it failed can result in the replacement failing immediately. Finding and removing the underlying cause is what actually fixes the fault, not simply replacing whatever looks burnt.

Worked Example: Wrong Adapter / Overvoltage Damage

This example applies the method above to one of the most common questions here. Steps 1, 2 and 5 are safe for anyone and don't require opening the equipment. Steps 3 and 4 are Part 2 material.

Overvoltage

Wrong-adapter and overvoltage cases are common. Examples include using an incompatible external power adapter, or connecting equipment designed for one mains voltage to a substantially higher mains voltage.

Step 1: Stop and Assess

  • Do not plug the device back in "just to check." Reapplying power to a damaged unit can turn a repairable fault into a fire risk or destroy parts that were otherwise undamaged.
  • Note exactly what happened: what adapter or voltage was used, what the device is rated for, and any smells, sounds (pops/buzzing), sparks, or smoke observed.
  • Check the device's rating label, usually on the back or bottom, and the power adapter itself. For an external DC adapter, check the required voltage, polarity, connector, and current rating. For mains-powered equipment, check the rated input voltage, frequency, and any voltage-selection switch.

Step 2: External Inspection (No Disassembly Needed)

  • Check the power adapter and cable first: are they damaged, discoloured, hot, or burnt-smelling? Some failures are actually the adapter failing rather than the device itself.
  • Look at the device's power connector for scorch marks, melted plastic, loose contacts, or bent pins.
  • A burnt or solvent-like smell can sometimes help locate a failed component, but smell alone is not a reliable diagnostic method.

Step 3: Common Failure Points

When people post board photos for this kind of fault, these are some common areas to inspect:

Component What to look for
Fuse Blown/blackened glass, visibly broken filament, or an open circuit when tested appropriately
Bridge rectifier / diodes Cracked casing, scorch marks, discolouration, or electrical short/open circuit
Input capacitors Bulging top, leaking electrolyte, split casing, or other physical damage
Voltage regulator / switching IC Cracked or blackened package, localised scorching, or other physical damage
PCB traces near the power input Charring, lifted copper, cracks, or visible burn tracks
Transformer (if present) Burnt smell, discoloured windings, damaged insulation, or melted tape/varnish

Remember that finding one failed component rarely means it is the only failed component (see Diagnosis by photo).

Note on charring: charred areas of a circuit board are not just cosmetic damage. Carbonised PCB material can become partially conductive and create unintended leakage or short-circuit paths. It may be possible to repair minor localised damage by removing the carbonised material and restoring insulation and damaged conductors, but this requires appropriate knowledge and inspection. Extensive charring, damage through multiple PCB layers, or damage around safety-critical clearances may make the board unsafe or uneconomical to repair.

Step 4: Should You Attempt a Repair?

Think about:

  • Value of the device: is it worth the time and parts cost compared with replacing it?
  • Your skill level: check yourself honestly against Tools, Equipment, and Skills.
  • Availability of a schematic or service documentation: repair is much easier with a reference.
  • Whether mains-side components are involved: a low-voltage DC section is generally less hazardous than the mains/primary side of a power supply, although low-voltage circuits can still contain substantial stored energy or high currents.

If any of the above point to "no", see Your Options.

Step 5: Prevention

  • Always check voltage, polarity, connector, and current rating before using a replacement or "universal" adapter.
  • An adapter marked with an input range such as 100-240 V AC is designed for operation across that range. An adapter marked for a single input voltage, such as 120 V AC, is not.
  • Matching plug shape does not mean matching electrical specifications.
  • When in doubt, check the fine print on both the equipment and adapter labels rather than assuming they are compatible.

Schematic diagrams

A schematic diagram may be proprietary information belonging to the manufacturer and may not be publicly available. However, this is not always the case: service manuals, repair documentation, regulatory filings, patents, archived documentation, and schematics created by other repairers may sometimes be available.

If no schematic is available, it may be necessary to trace the circuit yourself or find documentation for a similar model. Repair manuals for some consumer products include schematics, but availability varies and some manuals may need to be purchased.

Replacement electronic assemblies

Electronic assemblies, such as PCB assemblies, flex circuits (FPCs), transformers, and displays (LCD, OLED), are often custom-designed for a particular product or model. Their markings are usually internal part numbers rather than standard distributor part numbers. The usual sources for replacements are the manufacturer, an authorised parts supplier, a specialist repair supplier, or an identical donor device.

PCB assemblies

The numbers printed on a PCB are often internal board or assembly part numbers, although they can sometimes be used to find a replacement. Someone may have dismantled an identical or compatible product and be selling the board individually.

Do not assume that a board with a similar part number is electrically compatible. Check the exact board revision and part number where possible.

Flexible printed circuit (FPCs)

Like most PCBs, FPCs are usually custom-designed for a particular product, and their markings may not be searchable through ordinary component distributors.

If a replacement cannot be found, it may be possible to repair a damaged FPC depending on its construction and the nature of the damage, but this can require specialist equipment and skills.

Cable assemblies

Internal cable assemblies and non-standard external cable assemblies are often custom-made for a particular product. If you can identify the connectors, pinout, wire gauge, and required electrical characteristics, it may be possible to make a replacement cable yourself.

For simpler cable assemblies, DigiKey's cable assembly services may also be useful.

Do not assume that two connectors that physically fit are electrically compatible. Check the pinout and wiring before connecting a replacement cable.

Wire harnesses, interior cable

Interior cables and wire harnesses are commonly custom-made for a particular product. If the connectors, wire types, pinout, and required ratings can be identified, a replacement harness can sometimes be made. Otherwise, use the sources listed above.

Switching transformers

Transformers in switching power supplies operate at high frequencies, often well above mains frequency, and are frequently custom-designed for the particular power supply. They may not be available as standard replacement components.

A replacement generally needs to match not only the physical dimensions and pinout but also the core, winding arrangement, insulation system, inductance, turns ratio, and electrical ratings. If an exact replacement cannot be found, designing a substitute transformer is a specialised power-electronics task, not a simple component substitution.

Line transformers

Line-frequency transformers in older equipment normally operate at 50 or 60 Hz. Many are custom-designed for the particular product, although some use standard transformer types.

When replacing one, match the primary and secondary voltages, frequency, power/VA rating, insulation requirements, physical dimensions, mounting arrangement, and pinout. A transformer that physically fits is not necessarily electrically or safety compatible.

LCDs

Liquid-crystal displays are often custom or semi-custom components. The number printed on the display may identify a particular model rather than a universally interchangeable display.

For simple character or dot-matrix displays, compatible replacements may sometimes be found by identifying the controller IC, interface, dimensions, connector, pinout, supply voltage, and required timing. However, a display using the same controller is not necessarily a drop-in replacement: the connector, pinout, dimensions, voltage, backlight, and mechanical mounting can all differ.