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

Hot_Amir wrote:

If resisted. 1If the shunt resists 10آمپر را پیدا کنم چگونه و چه رابطه ای بین اون و شنت سوخته شده وجود دارد؟ چگونه من را به مقاومت سوخته موازی با 51 اهم میرساند؟

Added after 1 [minutes]:

به نظر می‌رسد که نیمه اول سوال شما به درستی کامل نشده است. من فرض می‌کنم که شما در حال پرسیدن درباره‌ی چگونگی یافتن مقاومت شنت برای دامنه 10 آمپر مولتی‌متر هستید و چه ارتباطی بین آن و شنت سوخته‌ی قبلی وجود دارد که با مقاومت 51 اهم موازی شده است.

برای روشن‌تر کردن این مسئله باید بدانیم که مقاومت‌های شنت در مولتی‌مترها با توجه به دامنه‌ی اندازه‌گیری جریان که قرار است استفاده شوند، انتخاب می‌شوند. مقاومت شنت برای دامنه‌ی جریان بالا (مانند 10 آمپر) معمولاً مقدار بسیار کمی دارد تا افت ولتاژ کمی ایجاد کند و در عین حال جریان زیادی را تحمل کند.

برای مثال، اگر مولتی‌متر شما برای اندازه‌گیری 10 آمپر روی یک افت ولتاژ حدود 200 میلی‌ولت طراحی شده باشد، مقاومت شنت باید برابر با:

$$ R = \frac{V}{I} = \frac{0.2V}{10A} = 0.02\Omega $$

باشد. بنابراین، شما به دنبال یک مقاومت شنت با مقدار 0.02 اهم خواهید بود.

اگر مقاومت 51 اهم به صورت موازی با شنت سوخته شده قرار گرفته است، این کار می‌تواند برای حفاظت یا اطمینان از ادامه کارایی مولتی‌متر در صورت خرابی شنت اصلی انجام شده باشد. در این حالت، مقاومت کلی کاهش یافته و این اجازه را می‌دهد که هنوز مقداری از جریان از طریق مقاومت 51 اهم عبور کند، اما دقت اندازه‌گیری‌ها تغییر خواهد کرد و نمی‌توان به آنها اعتماد کرد.

در این مرحله، برای تعمیر دستگاه، باید شنت اصلی را با یک شنت مناسب جایگزین کنید و سپس مولتی‌متر را دوباره کالیبره کنید. اطمینان حاصل کنید که همه دامنه‌های اندازه‌گیری جریان پس از تعمیر دقیق هستند و در صورت لزوم همراه با یک مولتی‌متر دقیق دیگر تست کنید.

اگر به کمک بیشتری نیاز دارید یا سوالات فنی دیگری در مورد این موضوع دارید، لطفاً اطلاع دهید.

Hot_Amir wrote:

(...) ours, which part of the feed will you be damaged? Where do I take the voltages?

Added after 4 [minutes]:

If I plug the multimeter into a 9-volt adapter instead of a 9-volt battery and the multimeter goes off after a few hours, which part of the feed will you be damaged? Where do I take the voltages?

Using a 9-volt adapter instead of a 9-volt battery can potentially cause issues if the adapter is not well-regulated or if the current provided is not within the specifications required by the multimeter. Here are some factors to consider and steps to follow:

1. Voltage Regulation: Make sure that the adapter is a regulated power supply that provides a stable 9 volts. An unregulated adapter might supply a higher voltage than expected, which can overheat or damage the components within the multimeter.

2. Current Rating: The adapter should also have the proper current rating. If it supplies too much current, it can lead to overheating. If it supplies too little, the multimeter may not function correctly or may turn off intermittently as it tries to draw more current than the adapter can supply.

3. Polarity: Check the polarity of the adapter's connector. If the polarity is reversed, it could damage the multimeter. The positive terminal of the power supply should match the positive input on the multimeter.

4. AC Ripple: If the adapter is not a pure DC power supply and has AC ripple, it could cause the multimeter to malfunction or shut down due to inconsistent power.

If the multimeter goes off after a few hours, it's possible that something in the power supply section is being damaged or is overheating. To diagnose the issue:

1. Visual Inspection: Begin with a visual inspection of the multimeter's PCB. Look for any signs of overheating, such as discolored components or melted solder.

2. Check the Power Input: Measure the voltage at the point where the adapter connects to the multimeter circuit to ensure it's stable and consistent with a 9-volt battery.

3. Voltage Regulator: If the multimeter has an onboard voltage regulator, check that it is functioning correctly. Measure the input and output voltages of the regulator. The output should be stable and within the specifications for the multimeter circuit.

4. Check Capacitors: Look at the capacitors in the power supply section for signs of bulging or leakage, which can indicate failure.

5. Check Diodes and Other Components: Diodes, resistors, and other components in the power supply path should be checked for proper operation.

6. Thermal Shutdown: Some components have a thermal shutdown feature. If something is overheating, this might shut off the device to prevent damage.

7. Intermittent Connection: An intermittent connection could also cause the device to turn off. Check solder joints and connectors for any signs of a bad connection.

If you are not comfortable with these diagnostic steps or if you don't have the necessary equipment, it might be wise to seek the help of a professional electronics technician. Repairing a multimeter yourself can be challenging, and there's a risk of causing further damage if you're not sure about what you're doing. Additionally, be cautious when working with power supplies to avoid electric shock or short circuits.

Hot_Amir wrote:

(...) d the adapter and left a new battery, but the multimeter does not turn on.
Guidance on Nutrition Troubleshooting

Added after 6 [minutes]:


@ElektrodaBot After power off, I disconnected the adapter and left a new battery, but the multimeter does not turn on.
Guidance on Nutrition Troubleshooting

It seems that your multimeter is not turning on after having used an external power adapter and subsequently switching back to a new battery. This indicates there may be an issue in the power supply section of the multimeter or other related components. Here is a step-by-step guide to troubleshoot the issue:

1. Check the Battery Connection: Ensure that the new battery is correctly installed with the right polarity and that the battery contacts are clean and making good contact.

2. Fuse Check: Some multimeters have a fuse that may blow if an incorrect voltage or current is supplied. Check if there's a fuse that's accessible and replace it if it's blown.

3. Visual Inspection: Open the multimeter and perform a visual inspection looking for any signs of damage, burning, or component failure. Pay special attention to the area where the external power was connected.

4. Voltage Regulator: If the multimeter has a voltage regulator, check it to ensure it is functioning correctly. Measure the input and the output of the voltage regulator using another working multimeter.

5. Continuity Check: Use another multimeter to check for continuity in the power supply path, including the power switch, battery connectors, and any in-line resistors or diodes.

6. Check Protection Diodes: Some multimeters have protection diodes to prevent damage from reverse polarity. Check if these diodes are functioning properly or if they have become shorted.

7. Power Supply Capacitors: Check the condition of any capacitors in the power supply circuit. They may be damaged due to overvoltage from the adapter.

8. Check the Main IC: If the power supply components seem intact, the problem could be with the main IC or other critical components that may have been damaged by an overvoltage or overcurrent condition.

9. Trace the Power Supply Circuit: Trace the circuit from the battery to the rest of the multimeter using the schematic if available. Look for any breaks in the trace or solder joints that may be causing an open circuit.

If you are not experienced with electronics repair, it may be safer and more time-efficient to consult a professional electronics technician for help. Since multimeters contain sensitive components that can be easily damaged, it's important to handle them carefully. If the multimeter is under warranty, consider contacting the manufacturer for support or replacement.