Here are my rules of thumb for troubleshooting electronic devices:
1. Confirm the problem
Confirm the problem before diving into the fix. Identification can start from:
- Ask the user to get as much information as possible.
- Reconstructing the sequence of events that resulted in the damage, whether it was purely an incident or due to human error.
My Rules of Troubleshooting
2. Safety first
Before making repairs, try to find out what hazards are associated with your repair equipment. Take precautions to ensure safety. Take it slow (be careful).
3. Always think about "what if"
This also applies to investigative actions. Do not neglect your equipment, provide protection for the probe tip (conductor) to prevent short circuits.
4. Always learn from mistakes
When making a mistake, never delay to evaluate. Some mistakes can result in big losses, simple problems such as probe tip slip can be a problem, so it costs more to restore it. Meanwhile, your experience is measured by how much effort you put in, so you can take points from the mistakes. We can all get important points through bad experiences first, such as carelessness, etc. What we need is only "How not to fall into the same hole again."
5. Always start with a simple analysis
Don't always start with test equipment such as a multitester and Don't immediately assume that your problem is some combination of complex damage. If the electronic device is also equipped with a mechanical system, then start your analysis from the easiest such as the mechanical system, which can be done with your 5 senses, this can also train your sensitivity to machine logic. Also prepare some alcohol, degreaser, contact cleaner, or light oil, if necessary.
6. Take a break
If you are tired and far from the solution approach, then there is no need to force it, so that you are trapped (unknowingly asleep) and your head is on the device, even forgetting to turn off all supporting equipment. This is very fatal, dangerous and unproductive. Better to take a break!
7. Simplifying Problems
If possible, try to isolate a particular module section from the main circuit. This includes efforts to narrow down the problem, so that we can find priority cases. This method is very safe for unit identification, because it can prevent possible effects that can affect other modules.
8. Preventive Maintenance
Don't blindly trust the instrument. If you find a measurement reading that doesn't make sense, then you need to suspect your instrument, perhaps it needs to be calibrated.
9. Take Notes
Whenever working on precision equipment, try to take simple notes, including pictures if necessary. You will be grateful for your notes when the time comes to reassemble the unit. Most connectors or cables are secured by a combination of a series, or a series of nearly identical but different screws. This is necessary because not all units come with a repair/disassembly manual.
10. Understand the risks of ESD (Electro-Static Discharge)
Understand the risk of ESD (Electro-Static Discharge). Some components such as ICs are very susceptible to ESD. The preventive measure is to ensure that your body is connected to a pure GND (Ground), not the ground of a device such as a transformer or casing. To get a pure ground, you may need to create a single channel buried in the ground several meters deep. Connect your wristrap to the channel and wear it every time you start operating.
How to Check & Test Electronic Circuits?
Continuity Testing
A number of problems can be identified by checking the PCB tracks for near zero resistance. An ohmmeter with Rx1 scale can be used for this.
With an audible tester such as the one in Figure 2.61 the eye can continue to monitor the circuit. Use the needle pointer to penetrate the oxide layer that forms the insulator, and make sure that the instrument under test is off.
Here are some possible places for continuity breakdown:
- Two ends of the cable (conductor or broken connector).
- The IC legs and circuit tracks on the PCB make for poor connections, especially if the IC uses a socket.
- Two long, thin ends of a track on a PCB.
- Fixed or moving switch or relay contacts (bent, broken or corroded switch contacts).
Short and Open Circuit
Figures 2.61(a) to (c) show the voltage distributions in a series circuit under normal, short-circuit, and open-circuit conditions.
To trace a short or open circuit in a series circuit, with an oscilloscope or voltmeter from ground to A, move to B, C, D, E, and F. The voltage drop to zero is observed at point F.
Figure 2.61: Continuity Tester With Audio
Normal series circuit and voltage to ground
A short circuit indicates that no voltage passes through the short circuited element.
An open circuit drops all voltage across the disconnected circuit.
If there is no voltage drop across some element until the incoming voltage is dropped, there may be a crack in the circuit, between D and E in Figure 2.61(c).
Figure 2.61.d: shows the voltage that produces power across a resistor. A resistor that is found to dissipate more power is therefore short-circuited. A resistor dissipating less than ¼ of its rated power is most likely an open circuit.
Graph to Determine Resistor Power Quickly
If one or more elements have a small / zero voltage, then a short circuit is suspected, but this does not apply to:
- Fuse elements, thermistors and coils show very small voltage drops, because they have very low resistance.
- Small resistors will drop small voltages, but values in the 100 ohm range are commonly used in series at the input and output of high-frequency amplifiers to prevent oscillation. This shows no voltage drop at signal and dc frequencies. Power supply decoupling resistors (Figure 2.62) in the 100 ohm to 1K ohm range also show no dc drop.
Figure 2.62: Rs As A Decoupling Resistor In A Power Supply
Certain resistors have no voltage drop under certain signal conditions but show voltage under other conditions. For example: the emitter resistor in a complementary-symmetrical power amplifier (Figure 2.63) or a class B pushpull amplifier has no drop, but will drop a volt or more at full signal.
Figure 2.63: Re in Complementary-Symmetrical Amplifier
Schmitt triggers, one shots, and flip-flops (figure 2.64) will show no drop across the collector resistor when the drop is nearly as large as VCC across the others.
Figure 2.64: Rc On Flip-Flop
Various Electronic Symbols
The following diagram illustrates active components, the difference between active and passive is that active components require a power source to operate, while passive components do not. The top symbol represents a vacuum tube or thermionic device. Although at one time, these were being replaced by smaller transistors and integrated circuits, they are finding their way back into electronics for use in professional audio equipment and some radio receivers.