Digital Multimeter LCD Display Not Turning On: Voltage Measurement & LCD Specs

Hot_Amir wrote:

If the digital multimeter selector is dirty, what is the best material to use? Except spray, alcohol, thinner and acetone .

Cleaning a multimeter selector switch (rotary dial) should be done with care to avoid damaging any internal components. Since you've ruled out the use of spray, alcohol, thinner, and acetone, there are still a few options you can consider:

1. Contact Cleaner: There are specialized contact cleaners available that are designed specifically for cleaning electrical contacts without damaging the plastics or the electronics. They typically come in a spray can, but I understand you're looking for alternatives to sprays.

2. DeoxIT: DeoxIT is a well-known cleaner and lubricant for electrical contacts. It's available in various forms, including wipes, which could be an alternative to using sprays.

3. Isopropyl Alcohol Pads: While you've mentioned excluding alcohol, if you meant liquid form, you might still consider using pre-saturated isopropyl alcohol wipes, which can be gently rubbed on the contacts to clean them without the risk of excess liquid damaging the multimeter.

4. Distilled Water and Mild Detergent: If the dirt isn't too stubborn, a mild solution of distilled water and a small amount of mild detergent can be used with a cotton swab or soft brush. Make sure to thoroughly dry the component after cleaning.

5. Dry Brush: Sometimes a simple, soft-bristled brush can remove loose dirt and dust without the need for any liquid cleaners.

6. Compressed Air: A can of compressed air can be used to blow out any dust or dirt from the switch without making physical contact. This doesn't involve liquids or chemicals and can be very effective for dry contaminants.

Remember, after cleaning with any liquid solution, it's important to allow the switch to dry completely before using the multimeter again to avoid any potential short-circuits. If you're using any form of liquid, use it sparingly to prevent it from seeping into areas where it could cause damage. Also, always ensure that the multimeter is off and the battery is removed before attempting to clean it.

Hot_Amir wrote:

(...) can I clean it without removing the selector? With a syringe, we pour the material on the copper contacts and the printed circuit. I dry it in compressed air or I don't use it for a few days. Is it the right thing to do? If it is true, what substances can I inject? What do you think is the correct work?

It's not uncommon for some multimeters to show fluctuating readings with movement or vibration of the selector switch, especially if there's a poor connection or dirt on the contacts. Here's how you can address this:

1. Cleaning Without Disassembly:
- Using a syringe to apply a cleaning solution can work, but you should be very careful to use only a small amount of liquid to avoid any possibility of liquid damage to the multimeter.
- After applying the cleaning solution, rotating the selector switch back and forth can help clean the contacts by rubbing them against each other.
- Using compressed air to dry the switch is a good idea, but you must ensure that the cleaner is fully evaporated before using the multimeter again. Allowing it to dry for a few days is typically unnecessary if you use compressed air, as it should evaporate quickly.

2. Cleaning Substances:
- A proper contact cleaner designed for electrical contacts is the best choice. These cleaners usually evaporate quickly and do not leave a residue. They are formulated to clean without damaging electronic components.
- DeoxIT contact cleaner and rejuvenator is another good option since it not only cleans but also improves the electrical connection.
- Isopropyl alcohol (preferably 99% purity) can be used if you don't have access to a specialized contact cleaner. It's less aggressive than other solvents and evaporates quickly, but ensure it's applied sparingly.

3. Correct Practice:
- Ensure the multimeter is turned off and the battery is removed before cleaning.
- Apply only a small amount of cleaning solution.
- Rotate the selector switch through its full range several times to help clean the contacts.
- Use compressed air to remove any excess cleaner and aid in drying.
- Wait until the solvent has completely evaporated before reassembling and using the multimeter.

If the problem persists after cleaning, it could indicate a more serious issue with the switch or other internal components. If you're not comfortable with cleaning it yourself, or if the multimeter is still under warranty, consider contacting the manufacturer or a professional for service.

Hot_Amir wrote:

20801526
Please explain more about this answer you gave me:
4. Test the LCD Itself: If you have a variable DC power supply, you can also apply a +3V signal directly to the VC+ and V0 (ground) of the LCD to see if it turns on.

Apologies, but it seems there might have been some confusion. I'd love to clarify any points, but I need a bit more context on what you're asking about when you mention "20801526."

However, regarding testing an LCD with a variable power supply, this is a common method used to check if an LCD panel from a device like a multimeter or another piece of electronics is functioning properly. The VC+ and V0 pins are commonly associated with the power supply for the LCD. VC+ would be the positive voltage supply, and V0 would typically be the ground or negative terminal.

Here's a more detailed explanation:

Caution: Only attempt this if you're confident in your understanding of electronics and the risks involved. Improperly powering the LCD can damage it.

1. Identify the Pins: Find the datasheet for the specific LCD or closely inspect the PCB to identify the power supply pins. VC+ is usually the positive voltage input, and V0 is often the ground reference.

2. Set Up the Power Supply: Set your variable DC power supply to the correct voltage for the LCD. Many small LCDs operate at around 3V, but you must check the specifications for your specific model.

3. Connect the Power Supply: Using fine wires or appropriate connectors, apply the positive voltage from the power supply to the VC+ pin of the LCD and the ground to the V0 pin.

4. Observe the LCD: Once powered, observe the LCD for any signs of life. This could be segments lighting up or the entire display coming on.

5. Adjust Contrast: If the LCD requires it, you might need to adjust a contrast voltage to see characters or segments clearly. This is sometimes done with a variable resistor or by applying a specific voltage to another pin designated for contrast control.

6. Conclusion: If the LCD lights up, it's likely functioning, and any issues with the device might be elsewhere. If it doesn't, the LCD module could be faulty.

Please note that this is a simplified explanation. Always refer to the specific LCD datasheet or service manual for the correct voltages and methods of testing. If you're unsure or the test setup doesn't match the device's operating conditions, it's best not to proceed to prevent any damage.

Could you provide more details or clarify what you're looking to understand better?

Hot_Amir wrote:

If I mix ethanol alcohol with a few drops of car engine oil, can I wash and clean the multimeter selector and its contacts? Maybe the LCD turned on.

Mixing ethanol alcohol with car engine oil to clean a multimeter selector and its contacts is not advisable for a few reasons:

1. Residue: Engine oil is designed to lubricate and protect engine parts, and it will leave a residue on the contacts. This oily residue could attract dust and dirt, leading to a build-up that could actually worsen the electrical contact over time.

2. Conductivity: Oil is not conductive, but it can form a film over the contacts that may impede electrical conductivity. A good contact cleaner for electronics will evaporate completely, leaving no residue, which is not the case with engine oil.

3. Compatibility: The chemicals in engine oil might not be compatible with the materials used in your multimeter. It could potentially damage plastic parts or the LCD if it comes into contact with them.

4. Safety: Mixing chemicals can sometimes lead to unexpected reactions, particularly if you're not sure how they will interact. It's best to use products as they are intended to be used and not mix them unless you are certain it's safe to do so.

5. Effect on the LCD: If your LCD turned on unintentionally during this process, it could indicate that the substance has seeped into places it shouldn't be. This could cause short-term operation but lead to long-term damage.

For cleaning electrical contacts, it is best to use a specific contact cleaner that is designed for use with electronics. These cleaners typically evaporate quickly and leave no residue, ensuring that the contacts are clean and will not attract additional dirt. After cleaning with an appropriate contact cleaner, if lubrication is necessary, use a cleaner with lubricating properties designed specifically for electronic contacts, such as DeoxIT.

If you're experiencing issues with the LCD, it's important to address those separately and with appropriate methods. Cleaning the contacts of the selector switch should not affect the LCD unless the cleaner has inadvertently reached the LCD's connections.

Remember to always follow the manufacturer's instructions for maintenance and only attempt repairs if you're confident in your ability to do so without causing damage. If the multimeter is under warranty, you should contact the manufacturer or a professional before attempting any DIY fixes that could void the warranty.

Hot_Amir wrote:

1-For example, R5 is written on the data sheet of the multimeter, but on the printed circuit board, it says 5R2. I'm lost. Can you help me?
2- I used a special spray. The selector was too tight. Don't you think it dries up the contacts too much?

Certainly! Let's break down your questions:

1. R5 vs. 5R2 Discrepancy:
- If the datasheet for your multimeter states "R5" and you find "5R2" on the printed circuit board (PCB), we're dealing with two different things. "R5" on the datasheet likely refers to the designator for a resistor in the schematic diagram or parts list (R is commonly used to denote resistors, and the number following it is the unique identifier for that part in the circuit). However, "5R2" on a resistor on the PCB is a code for the resistance value.

- The "5R2" marking on a resistor usually denotes its resistance value using a shorthand notation. The "R" stands for the decimal point, and the number before it represents the value before the decimal point, while the number after it represents the value after the decimal point. So "5R2" would be interpreted as 5.2 ohms.

- It's possible that there is either a misprint on the PCB or the datasheet, or there could be a version difference in the components used on the multimeter. It might also simply be a case of misreading the information. Can you provide a bit more context or even an image of the PCB marking and the datasheet reference? That would help in giving a more precise answer.

2. Using Special Spray on the Selector:
- It sounds like you used a lubricant or contact cleaner spray to loosen up a tight selector switch. Usually, a contact cleaner that's appropriate for electronics will evaporate and not leave a harmful residue. If it's a lubricant, it's meant to stay on the contact to keep it moving smoothly.

- If your concern is about the spray drying up the contacts too much, consider what type of spray you used. A contact cleaner designed for electronics should not cause any harm; it's supposed to clean and then evaporate without leaving a drying effect on the components. If you used a lubricating spray, it's supposed to leave a thin lubricating film that should not dry out the contacts.

- However, overuse of any substance could potentially cause issues. If you're worried about over-drying, the problem would usually be more about the cleaner potentially affecting other parts of the multimeter, such as plastic components, which could become brittle or crack if exposed to certain solvents. Always use these products sparingly and according to the manufacturer's instructions.

Can you tell me what kind of spray you used (contact cleaner, WD-40, silicone lubricant, etc.)? This information would let me give you more tailored advice.

Hot_Amir wrote:

Spray that I use is written by Dee Lubricant 600 . Does this information help?

Yes, this information does help. Dee Lubricant 600 appears to be a contact cleaner spray that's suitable for use in electronics. These types of sprays typically contain a solvent to clean away dirt, oxidation, and other contaminants from the contacts, and they may also contain a lubricant to ensure smooth operation of moving parts, such as selector switches or potentiometers.

When you use a product like Dee Lubricant 600, it's designed to achieve a couple of key outcomes:

1. Clean Contacts: The solvent part of the spray will clean the contacts, which could improve electrical conductivity and the overall performance of the selector switch.

2. Lubricate Mechanism: The lubricating component will help to reduce friction and wear on the moving parts, making the selector switch easier to turn without sticking or binding.

The product should not dry out the contacts in a harmful way. On the contrary, it will leave a protective lubricating layer that should maintain the functionality of the selector switch over time. However, it's important to use it correctly:

- Use in a Well-Ventilated Area: The solvents can be quite strong and potentially harmful if inhaled in concentrated amounts.
- Apply Sparingly: You only need a short burst of spray to treat the contacts—over-application can lead to excess fluid moving to unwanted areas of the multimeter.
- Avoid Overspray: Try to shield or protect other parts of the multimeter, especially the LCD and any plastic components, from the spray to avoid any potential damage.
- Follow Drying Time Instructions: Allow the spray to evaporate and the contacts to dry completely before using the multimeter again.

It's encouraging to hear that you've used a proper electronics contact cleaner and lubricant for your multimeter's selector switch. As a result, you should expect improved performance without adverse effects on the contacts. If you have any further questions or concerns about the procedure or the product, please let me know—I'm here to help!

Hot_Amir wrote:

I think that it will dry up contacts and move the switch stiff. Is this the standard or am I wrong?

If used correctly, Dee Lubricant 600, which is a contact cleaner and lubricant, should not cause the contacts to dry up or the switch to become stiff. In fact, its purpose is quite the opposite. It should clean the contacts by removing any dirt, grease, or oxidation and then leave behind a thin lubricating film that helps to keep the selector switch moving smoothly.

Here's what you can typically expect from a product like this:

1. Cleaning Action: The solvent in the cleaner removes contaminants from the contacts, which could otherwise cause poor electrical connection or intermittent signals.

2. Lubrication: After the cleaning solvent evaporates, the lubricant remains to reduce friction and facilitate easy movement of the switch.

However, there are a few scenarios where you might end up with a stiff switch after use:

- Over-application: Using too much spray can lead to excess lubricant, which might attract dust and debris over time, causing the switch to feel gummy or stiff.

- Incorrect Product: If the product is not suitable for the material of the switch or if it's not a high-quality electronics lubricant, it could potentially cause issues.

- Pre-existing Conditions: If the switch was already damaged or worn out, the cleaner might not be able to fully restore its function.

If you've used the spray sparingly and the switch has become stiff after use, it could be due to the switch mechanism itself having issues, or perhaps the product didn't have enough time to fully evaporate before you tested the switch. If the stiffness persists, you may want to carefully reapply a very small amount of the lubricant, making sure it penetrates into the switch mechanism without overdoing it.

Remember to always follow the manufacturer's instructions for the contact cleaner and only use amounts as directed. If the problem continues, there might be a mechanical issue with the selector switch that needs a closer look or potentially a replacement switch. Could you tell me how long you waited for the product to evaporate before testing the switch? And how much of the lubricant did you apply?

Hot_Amir wrote:

Why do they write 5R2 instead of the SMD resistance number on some printed circuits? The resistance value on the SMD is written with a code. What does this text mean in printed circuit fiber?
@ElektrodaBot Why do they write 5R2 instead of the SMD resistance number on some printed circuits? The resistance value on the SMD is written with a code. What does this text mean in printed circuit fiber?

It seems there might be a bit of confusion here. To clarify, "5R2" written on a printed circuit board (PCB) next to a resistor usually indicates the resistance value of that particular resistor, which in this case is 5.2 ohms. "R" in this context represents the decimal point.

When it comes to Surface-Mount Device (SMD) resistors, manufacturers typically use a three-digit or four-digit code to indicate resistance values. For example, a code "522" would mean a 5.2k ohm resistor (52 followed by 2 more zeroes), while "5R2" would simply be a shorthand for a 5.2 ohm resistor without using a digit code.

The reason for using such shorthand notations like "5R2" on the PCB could be due to several reasons:

- Space Constraints: SMD components are very small and there might not be enough space to print the full resistance value in a way that's easily readable, so a shorthand notation is used.

- Standardization: This notation is quite common and is easily understood by those familiar with electronics manufacturing and assembly.

- Clarity: This method avoids confusion with the SMD codes that might be interpreted in multiple ways, ensuring that the intended value is clear.

On the PCB, however, you're more likely to see such shorthand notations used in the silkscreen layer, which provides a human-readable indication of the component value to assist in manual inspection or repair.

If you're still in doubt about the resistor value, using a multimeter to measure the resistance is always the most reliable method. Regarding your original question about the multimeter datasheet and PCB discrepancy, I'd suggest checking whether the datasheet might be referring to the part identifier (like "R5" meaning resistor number 5 on the schematic) which is different from the resistor value ("5R2" meaning a 5.2 ohms resistor).

Is there a specific reason you are looking into the resistor values on the PCB? Are you troubleshooting or designing something? Maybe I can help with more targeted advice if I have more context.

Hot_Amir wrote:

I'm doing a multimeter repair. On Printed Circuit Board Fiber says 5R2, 5R3 and R5 These are three SMD resistors that have a certain amount written on them, but in the datasheet there are no such numbers, only R + number. Is it standard for the name of this book? What does it mean? why is it written like that? I don't mean the amount of resistance.

Ah, I understand now. In the context of multimeter repair and PCB notation, "5R2" and "5R3" are likely references to the physical locations or identifiers of specific resistors on the PCB rather than their resistance values. These labels serve as unique identifiers for each component on the board, corresponding with the reference designators used in the schematic diagram and the bill of materials (BOM).

Here's how you might interpret these labels:

- 5R2 and 5R3: These could be identifiers for resistors in a specific section or part of the circuit. The "5" might indicate a particular circuit block or section number on the PCB, while the "R2" and "R3" would stand for the second and third resistors within that block.

- R5: This is a more straightforward reference designator that indicates resistor number 5 on the schematic and PCB.

In electronics schematics and PCB design, it is standard to label components with a letter representing the component type followed by a number to differentiate it from other similar components. For example, resistors are labeled with "R", capacitors with "C", integrated circuits with "IC", and so on, followed by a unique number. This system helps technicians and engineers quickly locate and reference components during assembly, testing, and repair.

The reason you might not find "5R2" or "5R3" in the datasheet is that the datasheet often provides the electrical specification for the components rather than specific PCB layout information. The layout information is usually found in the service manual or the PCB design files if available.

For your repair, you would typically cross-reference these identifiers with the schematic diagram to find the required electrical specifications (like resistance, power rating, etc.) for each component. If you don't have access to the full service manual or the schematic, you might have to rely on context clues from the circuit or attempt to reverse-engineer the part of the circuit where these resistors are located.

If you need further assistance, could you provide more information or the context in which these resistors are used? It might help in giving you more specific guidance.

Hot_Amir wrote:

How do I reverse engineer a multimeter repair? Explain more and more clearly, and thank you for your guidance.

Reverse engineering a multimeter, or any electronic device for that matter, involves understanding how the device works by carefully analyzing its components and circuitry. It's a meticulous task that requires patience and a systematic approach. Here's a step-by-step guide to help you reverse engineer your multimeter for repair:

1. Documentation: Start by documenting the current state of the multimeter. Take high-resolution photos of the PCB from all angles. This will serve as a reference for where each component is placed and how it's connected.

2. Identification: Identify all visible components and their values. For resistors, you'll use their color codes or SMD markings. For capacitors, inductors, ICs, diodes, and transistors, you'll need to read their markings and possibly look up datasheets for their specifications.

3. Circuit Tracing: Begin tracing the circuit from a point you understand, like the power input or battery terminals. Use a multimeter to test continuity between components to understand how they're connected. Draw the connections as you trace them, either on paper or using a circuit diagram software.

4. Block Diagram: Create a high-level block diagram showing the main functional sections of the multimeter, such as the power supply, input selector, measurement circuit, display driver, and processor, if applicable.

5. Functional Analysis: Analyze how each block of the circuit functions. For instance, the input selector determines which type of measurement is being made (e.g., voltage, current, resistance), the measurement circuit processes the input signal, the display driver converts the processed signal into a readable format, etc.

6. Signal Flow: Understand the flow of the signal through the multimeter. Starting from the probes, see how the input signal is conditioned, scaled, and converted into a form that can be displayed.

7. Schematic Drawing: As you trace the circuit and understand more about how it works, begin drawing a schematic. Schematics are essential for understanding complex circuits and for troubleshooting.

8. Component Testing: Test each component to ensure it's functioning correctly. Resistors, capacitors, diodes, and transistors can all be tested with a multimeter. Integrated circuits may require more sophisticated methods to test.

9. Consult Forums and Communities: Engage with online communities, such as Elektroda, where you can share your findings and ask for help from other experienced electronics enthusiasts and professionals.

10. Hypothesize and Test: As you discover more about the non-working parts of the multimeter, form hypotheses about what might be wrong. Then, test these hypotheses by replacing components, bridging connections, or simulating signals.

Remember, safety first! Always make sure the multimeter is not connected to any power source when you're disassembling it or testing components.

Reverse engineering can also reveal proprietary circuit designs, so be aware of potential legal and ethical considerations if you intend to share or use the information publicly.

Is there a specific section of the multimeter you're having trouble with, or a particular symptom that's prompting the repair? Knowing more details can help provide more targeted advice.

Hot_Amir wrote:

(...) amount of resistance and its size. If you recall, the printed circuit was written under the SMD resistance 5R2. And the most important size of the resistor is written on it as code, but in the data sheet this text is not written and R5 is written. Exist. Please explain and teach more about this, please.

I see where the confusion lies. Let's try to clarify the differences between the resistor value markings on the SMD resistor itself, the labeling on the PCB, and the notations in the datasheet.

1. SMD Resistor Markings:
- The code on an SMD resistor indicates its resistance value. Resistors can use a 3-digit or 4-digit code. In a 3-digit code, the first two digits indicate the significant figures, and the third digit indicates the multiplier (number of zeros to follow). For example, "522" would be 52 followed by two zeros, meaning 5200 ohms or 5.2k ohms.
- In a 4-digit code, the first three digits are the significant figures, and the fourth is the multiplier. For example, "7501" would be 750 followed by one zero, meaning 7500 ohms or 7.5k ohms.
- Sometimes, the resistance is indicated in a format like "5R2", which would mean 5.2 ohms — the "R" stands in for the decimal point.

2. PCB Labeling:
- The PCB might have "5R2" printed next to an SMD resistor footprint, but in this case, instead of indicating the resistor value, it's highly likely that "5R2" is a reference designator. This is part of the unique identifier for the part on the PCB and helps locate the part on the board during manufacturing and troubleshooting. This reference does not necessarily indicate the resistance value but rather a positional reference.
- For instance, "5R2" could mean that this is the second resistor (R2) in section 5 of the PCB, or it could be a unique identifier unrelated to the sectioning of the board.

3. Datasheet Notations:
- In a datasheet or schematic diagram, resistors are typically labeled with an "R" followed by a unique number, like "R5." This labeling system doesn't indicate the resistor's value; it's purely for identification. The actual value of the resistor would be listed in a separate parts list or bill of materials (BOM).
- The datasheet or schematic won't necessarily tell you the location of the resistor on the physical PCB. It just helps you identify that there is a resistor, labeled as "R5" in the circuit, and you should refer to the BOM or accompanying documentation for its value.

Size:
- The physical size of the resistor doesn't usually have a direct relationship with the code printed on it; the size is determined by the power rating and the required precision. Common SMD resistor sizes (or packages) include 0402, 0603, 0805, 1206, and so forth, which correspond to their length and width in inches or millimeters, depending on the standard used.

To find the value of the resistor marked as R5 in the datasheet:
- Look for a parts list, BOM, or a detailed description in the datasheet that corresponds to the identifiers like "R5." It should provide the value and other specifications of the resistor.
- If this information is not available, you will need to deduce the value based on the circuit's function or measure it with a multimeter if possible.

In summary, "5R2" on the PCB is likely a reference designator and not the resistor's value. "R5" in the datasheet is the identifier for the resistor, and you need to look at the parts list or BOM to find the resistor's value, which might be unrelated to the number "5."

If you could provide the exact context or a photo of the PCB and the part of the datasheet you're referring to, I could give you a more precise explanation.

Hot_Amir wrote:

If the multimeter circuit data sheet is written in front of the resistor R5=10 KF. Indicates the amount of resistance? Or is it something else?

In the context you're describing, "R5=10 KF" in the datasheet is a bit unusual. Typically, resistance values are given in ohms (Ω), kilohms (kΩ), or megohms (MΩ), and "KF" doesn't align with standard notations for resistive values.

There are a couple of interpretations of "R5=10 KF":

1. Typographical Error: It might be a typo or misprint in the datasheet, where "KF" was intended to be "kΩ" (kilohms). In this case, "R5=10 kΩ" would mean that the resistor labeled as R5 on the circuit diagram and PCB should have a value of 10 kilohms.

2. Manufacturer-Specific Code: "KF" could be a manufacturer-specific code or internal designation that refers to something unique about the resistor, such as its tolerance, temperature coefficient, or another characteristic. This is less common, and you would normally refer to the manufacturer's documentation to decode this.

3. Series Designation: In some rare cases, manufacturers might use a code like "KF" to indicate a series or model of components, which would dictate its specifications. Again, this would usually be explained in a manufacturer's catalog or notes in the datasheet.

Given the context of your question, the most likely scenario is that "R5=10 KF" means "R5=10 kΩ," and the "KF" is an error or a misinterpretation. If possible, verify this by looking at other parts of the datasheet or service manual for consistent notation. You could also measure the resistance of R5 with a multimeter if you have access to the actual component on the PCB.

Do you have any additional context or documentation that might shed light on this "KF" notation? It might help to look at other components in the same datasheet to see if a similar notation is used elsewhere.

Hot_Amir wrote:

Shunt resistance of the burned and blackened ampere multimeter data sheet I could not get on the Internet. Paralleled by a 51 ohm resistor. What do you think I should do?

If you're dealing with a burnt and blackened shunt resistor in a multimeter, and you can't find the original value because it's not stated in the datasheet or service manual, here's what you can do:

1. Research: Try to find a service manual or schematic for the specific model of the multimeter online. Sometimes, these documents can be found in forums, specialized websites, or by directly contacting the manufacturer.

2. Estimation: If there's no documentation available, estimate the value based on standard multimeter designs. Many multimeters use a low-value shunt resistor for current measurement, often in the range of milliohms to a few ohms, depending on the maximum current range of the meter.

3. Parallel Resistor: If you have paralleled a 51-ohm resistor as a temporary fix, this is likely much too high for a shunt resistor, as shunt resistors are meant to have very low resistance to minimize their impact on the measurement circuit.

4. Reverse Engineering: Try to reverse-engineer the current measurement circuit. Look at the range switch and circuit configuration to deduce the expected value of the shunt resistor. This could involve looking at the voltage drop across the shunt at a given current and working out the required resistance using Ohm's law (V=IR).

5. Compare Models: If you have access to a multimeter of the same model that is functioning, you can measure the resistance of the shunt resistor in that unit. If you don't have the same model, you might compare with similar models and use their shunt resistor values as a starting point.

6. Trial and Error: As a last resort, you can use trial and error with low-value resistors or even a potentiometer to find a value that provides accurate readings. This method requires careful monitoring and calibration against a known good meter.

7. Calibration: After installing a new shunt resistor, you will likely need to calibrate the multimeter. You'll need a known good current source and another multimeter that is accurate to compare the readings and adjust the shunt value accordingly.

8. Safety Precautions: Keep in mind that modifying a multimeter, especially its current measurement circuitry, can be dangerous. Incorrect modifications can lead to inaccurate readings, damage to the device you're testing, or even hazards to your safety.

Please proceed with caution and consider seeking help from professional electronics repair services if you're not comfortable with these steps. Could you provide any more details about your multimeter model or the specific range that's been affected by the damaged shunt resistor? This information might help in offering more precise guidance.

Hot_Amir wrote:

Continuing the previous question: By the manufacturer of the 51 ohm resistance parallel to the burnt resistance, not me. Please answer this question

I understand now. If the manufacturer has placed a 51-ohm resistor in parallel with the burnt shunt resistor, it's likely that the 51-ohm resistor is serving as a temporary or backup current-sensing path. This approach might have been taken to ensure that some functionality is maintained even if the primary shunt resistor fails.

Here's what you might consider doing in this situation:

1. Understand the Purpose: Try to determine if the 51-ohm resistor is meant to be part of the original design (e.g., for a high-current range) or if it's a modification for some other reason. It's unusual for a shunt resistor in a multimeter to be this high unless it's used for a very low current range.

2. Identify the Original Shunt: Inspect the original shunt resistor that has been damaged. Look for any remaining identifiable marks or part of the resistor that isn't damaged. Sometimes, you can find a portion of the resistor that still has readable markings.

3. Schematic Analysis: Analyze the surrounding circuitry if a schematic is available. See if there are any clues about the expected current range and thus the potential value of the original shunt resistor.

4. Manufacturer Inquiry: Reach out to the manufacturer's technical support or customer service. They may be able to provide you with the value of the original shunt resistor or offer repair services.

5. Calculate Shunt Value: If the multimeter's current measuring ranges are known, you could calculate an approximate value for the shunt resistor. For example, if the multimeter has a range of 10A and uses a 200mV meter movement, the shunt resistor would need to be 200mV/10A = 0.02 ohms.

6. Check for Safety Features: It's possible that the 51-ohm resistor serves as a sort of fuse or safety feature, designed to become the path of least resistance in case the main shunt fails, to prevent further damage or hazard. Verify if this is the case before making any changes.

7. Consider Professional Repair: If you're not confident in making these determinations or if the repair seems complex, it might be best to consult a professional repair service or consider replacing the multimeter.

It's still a bit unclear why a 51-ohm resistor would be used in this way, as it would significantly impact the accuracy of the current measurement. If you can provide more details about the make and model of the multimeter or its intended current measurement capabilities, I might be able to offer more specific advice.

Hot_Amir wrote:

The multimeter only measures DC amps and can measure the range of 200 micro - 2 millimeters - 20 millimeters 200 millimeters and 10 amps. The ANENG digital multimeter model is AN830L. You said this information could help you respond.

Thank you for providing the details about the ANENG AN830L multimeter. Given the current measurement ranges you've described, it's clear that the multimeter is designed to measure small DC currents ranging from 200 microamps (µA) to 10 amps (A).

The presence of a 51-ohm resistor in parallel with the shunt resistor indicates that this resistor is part of the design for measuring smaller currents, as the voltage drop across a 51-ohm resistor would be too high for the larger current ranges (for example, at 10A, the drop would be 510 volts, which is unreasonable and unsafe).

Here are some steps you could take to address the issue:

1. Identify the Shunt for Large Currents: Usually, multimeters use separate shunt resistors for different current ranges. The 51-ohm resistor is likely for the microamp to milliamp ranges. The shunt for the 10A range would be a separate, much lower-value resistor, possibly in the range of a few milliohms, to handle higher currents.

2. Visual Inspection: Carefully inspect the PCB and look for another shunt resistor that's dedicated to the 10A range. This shunt is usually robust and might be a large metal strip or a thick wire that can handle high currents without significant heating.

3. Trace the Circuit: Follow the current path on the PCB from the 10A input jack to identify the main shunt resistor. If it's not immediately apparent, you may need to remove the PCB from the casing and inspect both sides.

4. Replacement: If you can identify the damaged shunt, it may be possible to replace it with a similar one. You might find a shunt resistor from an electronics supplier, or you might have to salvage one from a similar or identical multimeter.

5. Measure and Calculate: If you can still measure the resistance of the damaged shunt (despite it being burnt), you can use that value as a starting point for finding a replacement. If the shunt is completely unmeasurable, consider the typical voltage drop across the shunt at maximum current (usually around 200 mV to 250 mV for handheld multimeters) and use that to calculate the expected resistance using Ohm's law (Voltage = Current x Resistance).

6. Verify Ranges and Calibration: After replacing the shunt, you'll need to ensure that all current ranges are still accurate. This will likely require calibration against a known standard or another calibrated multimeter.

7. Consult the Manufacturer: As a last resort, reach out to ANENG or search for official repair resources. They may offer further guidance or replacement parts.

Due to the risk of incorrect current readings after such a repair, which can be dangerous or damaging, it's advisable to only undertake such repairs if you are experienced with electronics. Otherwise, it might be safer and more cost-effective to replace the multimeter. Given that the ANENG AN830L is a relatively inexpensive model, you should carefully consider the cost and safety implications of repair versus replacement.