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Learn From My Mistake In Using Sunwa Analogue Multimeter
There is no doubt that the Sunwa Analogue meter is one of my favorite meters in electronics troubleshooting. I have used this meter since the early days (mid of 80’s) I ventured into electronics repair. So many types of electronic components it can check and I just can’t do the repair work without it. It already helped me in so many repair jobs and the meter already paid itself back thousands of times!
Recently there was a customer sent in a laser printer for repair and the complaint was no power. I found that that main fuse was good so I disassembled the circuit board from the casing. I checked on the big filter capacitor and made sure there was no voltage so that I can begin to work on the board. The voltage reading of the capacitor was zero volts and this means I can start to check on the component. The moment I placed my test probes (set to x 1 Ohm) on the power FET pins (to check if FET is shorted or not) I could hear a loud sound “Poof” from my new Sunwa analogue meter.
I experienced this before in the old Sunwa meter model. I knew that the internal resistor of the meter could have blown and the cause of the problem usually was due to the un-discharged voltage in the main big filter capacitor. But I had checked earlier that there were zero volts across the main filter capacitor. Later I realized that one of my meter probes actually had an intermittent loose connection. It did not insert properly into the connector. This is my mistake and I should have check the test probes first before performing any repair work.
This is the reason why I got zero volt when measuring the voltage across the main filter capacitor. After connecting back the probe and rechecked the main filter capacitor (set to 1000VDC) it was showing about 300VDC wow! This also proven that the laser printer itself already have problem. Due to the intermittent loose connection in one of the test probes, my new meter was blown.
Well, as a repairer I have to open up the meter and start to repair it. Since this is a newest Sunwa analogue meter thus many SMD resistors were used in the circuit board.
Upon close inspection in the X1 Ohm range area I saw 2 SMD resistors with the value of 36R5, one of them already had a burnt mark. Both resistors tested open circuit. There were another one SMD resistor with a coding of 2000 (200 Ohms) also had an open circuit. It was replaced with a 220 Ohm SMD resistor.
I don’t have info for this SMD resistor code 36R5. The question now is how to read this SMD code? Here is the tip, when I checked on other good SMD resistors in the meter circuit board I found that 10R0 was 10 Ohm, 7R87 was 7.8 Ohm so this 36R5 should be 36 Ohm. I don’t have the info for “5” (36R5) or even “7” (7R87) at the end of the resistor.
Note: If you have the info please do leave a comment at the end of this article-thanks.
Since these two identical SMD resistors was connected parallel in the circuit this means the total value is 18 ohm based on the resistor parallel formula.
If you owned the older model of Sunwa 360 TRe analogue multimeter I believe you have replaced the X1 Ohm resistor before and the value was also 18 Ohm. Why X1 Ohm resistor value? Because this is the most frequent range that we use to perform checking and troubleshooting. This is why the failure rate is high on the X 1 Ohm range.
Since I don’t have the parts for the SMD resistor so I used carbon film ½ watt 18 Ohm as replacement. If I have 1/8 watt or 1/4 watt I will definitely use it. After I have soldered the resistor, I performed the value test to see if it still produces accurate reading or not. Check out the photo below:
Conclusion- If you own this type of meter and if the X1 Ohm internal resistor have problem you can always use 18 Ohm carbon film resistor as replacement. In the future if you came across SMD resistors coding that you don’t understand, always refer to the surrounding SMD resistors coding for answer. One more thing, always make sure the test probes are connected properly to avoid any future problem to the meter. My mistake can be your gain.
By the way if you want to learn how to use multimeter to perform troubleshooting in electronics circuit you can check out my Ebook HERE for more information.
You may also interested in this article too “10 Reasons How You Can Increase Your Electronics Repair Rate”