Servicing Sunma YX-3600Treb Analogue Multimeter

By on September 26, 2017
sunwa multimeter repairing and fixing

 

 

 

 

 

 

 

 

 

 

 

 

sunwa multimeter repair

Until I read the importance of using Analogue Multimeters from Jestine Yong, I was using Digital Multimeter for many years, though I had a BPL Analogue Multimeter from the yester years (my first test instrument), which was using Taut Band Suspension instead of the pivot and jewel. Often, our Multimeters might become defective either due to wearing out of contacts or some carelessness in use. I have repaired them in the past whenever possible, including retouching the worn out tracks with lead, spreading it evenly etc. Servicing a broken taut band suspension is almost impossible as we need precision instruments to refit like in the factory. But Pivot and Jewel type can be adjusted and balanced properly; but again is a very intricate job.




The Analogue Multimeter that I bought for my service in the Hospital, developed a problem. It was showing ‘0’ in X1 range, even where in reality it was not. I did not realize it, and did a lot of unwanted probing while servicing an SMPS, thinking that there was a short in the secondary side! (My Multimeter was showing dead short between + and -!) Only when I opened a working piece and found that the Multimeter was showing same reading there also, better sense dawned in me and I turned my attention to this MM. So, I opened the back cover and took a couple of snaps to record which wires go where. If we do not do it, if any wire breaks off, it might be difficult to find out where it was connected. This is especially true, when more than one wire breaks off!

how to fix sunwa multimeter

As you will notice from the first picture on the top, this Multimeter uses 2xAA batteries for X1 range and a 9V battery for x10 and upwards ranges. Mr. Jestine Yong had detailed in his number of books, how these two ranges are different in its working, and how we can use it for checking components. The only one PCB, is snapped in place by three plastic holders. I pried each one of them carefully and removed the PCB for taking the above two snaps. Then, kept the rotary switch in X1 position and checked where the three contacts underneath the switch touch. Please see the following snap:

how to repair sunwa multimeter

Then tracked the connections and found that it has one SMD resistor marked as 100 (for TEN Ohms).  When I checked with my SMD Tester, it showed very high value. Knowing Chinese tricks on using different value resistors in their circuits I checked another resistor on the board which also had 100 marked on it. It showed 10 Ohms. Then I knew that this was the culprit. I placed my soldering iron on top of this resistor, after applying flux, and it came out very easily.  I rechecked the resistor and found it was showing very high resistance:

sigma smart tweezers

Took out one ordinary ¼ W resistor, cleaned the leads with tweezer, and routed one end through a hole found near the resistor, from the other side of the board, and soldered it in place.




Then I soldered the other end on top itself to a jumper wire which was coming to the other side of the SMD resistor (negative path from the battery).

how to fix sunwa analog multimeter

The Multimeter functioned very well after that in the X1 range, bringing relief to me. Another hard lesson learnt (perhaps again and again!) how our test instruments can mislead us! In this case, I think it was some sort of over-confidence that I ignored this possibility, in spite of checking with a DMM and finding a different reading!

Anyhow, a happy ending!

This article was prepared for you by Parasuraman Subramanian from India. He is 68 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done  graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.




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You may check on his previous repair article below:

http://jestineyong.com/471k-mov-cracked-in-led-tv-repaired/

 

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19 Comments

  1. suranag Electronics

    September 26, 2017 at 1:49 pm

    Wow.. nice Repair
    MR.Parasuraman,
    Thanks you !

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  2. Albert

    September 26, 2017 at 1:55 pm

    Keeping our test equipment in good working order is like a repair job already half done! Thank you for another satisfactory job done Parasuraman! I however hardly use any old analogue multimeter anymore.
    And I still wonder why they are preferred over the digital ones which have a much higher input impedance and therefore hardly influence the measurements made in a circuit. The only disadvantage in my opinion is the need of a 9V block battery for them to operate. (A mini-penlight AAA or penlight AA battery operated DMM would be nice!)

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    • Robert Calk

      September 26, 2017 at 10:24 pm

      Because the analog meter with X10K (9V battery) allows the meter to test with higher voltage than most DMM's. I usually only use my VOM to test diodes, diacs and such. I used my BK Precision VOM in this article: http://jestineyong.com/lights-of-america-shop-light-repaired/

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      • Albert

        September 28, 2017 at 8:09 am

        I know Robert, and I remember that article about the use of a good analogue meter. But I only own an old big Russian analogue multimeter that I keep unused in its original aluminium case (certainly not an expensive one like your BK Precision).
        Like you I also have those Peak Atlas SCR-100 and a DCA75 Pro meters, and also a few other modern battery operated multitesters (including one that can test opamps, TTL/Cmos chips, zeners, some amplifier chips, and even optocouplers).
        Anyhow we both have other modern digital meters/test equipment that can provide us with the information we need like our DY294 that can test
        components under HV conditions that our DMMs simply can't. And like you I also have a special AR907A+ digital Insulation tester. Which makes me wonder why we have to use an old analogue meter like your BK Precision VOM to test DIACs, also named bidirectional symmetrical trigger diodes or DIode Alternating Current switch? Can't the DY294 and the AR907A+ not also test these? (I do not have a Diac at hand to test this so I take it that you already had tried this?).

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        • Robert Calk

          September 28, 2017 at 4:05 pm

          I'm no expert on test equipment, but the VOM with X10K will test at higher voltage than DMM's. I don't use the DY294 for diodes and such except for zeners. VOM's are usually more affordable for most people.

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          • Albert

            September 28, 2017 at 8:44 pm

            Sadly Robert the BK precision or comparable analogue MMs (AMMs ?) that I looked up on eBay,Aliexpress or others are much too expensive compared to any brandnew DY-294 meter. I have seen analogue VOM prices that exceed the price of the DY-294 at least 4 times! My guess is that they are simply over-priced because they are becoming scarce, not being manufactured anymore and therefore hardly being sold.
            The DY294 is ideal for measuring breakthrough voltages, so likely also capable of testing breakthrough voltages of DIACs. I probably have a DIAC diode laying around somewhere but finding it is hard because it probably isn't marked as being a DIAC. But when I find one I will give it a HV test on my DY294.

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            • Robert Calk

              September 29, 2017 at 1:05 am

              Yeah, the BK Precision 114A like mine are not very cheap since they are no longer made. But there are others that are pretty inexpensive and some you can get in kit form and put together yourself. I have one that was one of the first kits I put together when I first started learning electronics and soldering. I think it is a Tenma.
              There is a pretty good article on analog meters in the new October issue of Nuts and Volts magazine. For those in other countries you can get the magazine digitally pretty cheap.

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              • Albert

                October 14, 2017 at 10:16 am

                As I already expected is the DY294 also perfectly able to test any DIAC.
                I've just tested this with a DB3 DIAC that according to this datasheet has an breakthrough voltage of 28V.

                http://www.st.com/content/ccc/resource/technical/document/datasheet/fb/af/b0/56/99/1a/42/b4/CD00002277.pdf/files/CD00002277.pdf/jcr:content/translations/en.CD00002277.pdf

                And that is exactly what my DY294 showed on its display when tested in the capacitor voltage clamps on maximum voltage scale. And in both directions!

                Although it may not explicitly been written in the DY294 manual but it supports testing DIACs also just fine.
                So no need to use any old analogue meter!

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  3. Yogesh Panchal

    September 26, 2017 at 2:12 pm

    Good Job! Sir
    Reviving the old tools fabulous.

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  4. Robert Calk

    September 26, 2017 at 10:27 pm

    Good job, Parasuraman. That Sunma meter does not look like it is of very good quality. Be careful my friend.

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    • Parasuraman

      September 27, 2017 at 10:21 pm

      There is limitation when we buy tools for an institution like Hospital, especially when it is doing a lot of charitable health care. So, I am carrying my ESR Meter, digital SMD tester, blue Ring Tester, Peak Atlas and Another tool that can be used to test Monitors without the need for a Computer System, daily up and down, as I do not want to burden the Hospital.In fact I had volunteered to do electronic in-house servicing myself, though the management was hesitant to give another burden to me. So, I enjoy doing service in the hospital, during my free time. I hate to sit idle!

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      • Robert Calk

        September 28, 2017 at 4:09 pm

        You're a very good man. I hate to sit around doing nothing also. I guess that's why I have a lot of hobbies.

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  5. Henrique Jorge Guimarães Ulbrich

    September 26, 2017 at 10:42 pm

    The choice of using digital or analogue instrument depends on the type of measurement being performed. In certain cases (for example, when the value to be measured presents small oscilations), the analogue one is indicated, as the digital instrument gets confused due to the sampling method, that renders it difficulties to determine the mean value. For circuits with low or medium impedance (the most part of the circuits) the analogue instrument does not burden the circuit, so no problem with measuring accuracy. Moreover, in maintenance works the exact value is not necessary, so the precision of the digital instrument is not relevant.

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  6. Ding Villanueva

    September 29, 2017 at 11:41 pm

    Hi Mr Parasuraman,

    Greetings from the Philippines

    I also have two Sunma Analogue MM that needs some fixing. However, I can't find its schematic diagram so that I can replaced a burned out resistors.
    I wonder if you have a copy of the schematic for the same Sunma that you just repaied recently.

    Can you please send me a copy if I am not asking too much.

    Thank you and more power.

    Ding

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    • Parasuraman

      October 1, 2017 at 10:31 am

      Sorry, dear, I do not have. Perhaps you can trace it from the photos given in article?

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  7. Amir Mukhtar Ashrafi

    October 4, 2017 at 1:40 pm

    Thank you Mr. Parasuraman Subramanian
    Also, More thanks to Chineese conspiracy tricks for Resistor's wrong Showing Value like 100 = 10 ohms.

    Thank you Again
    Keep sharing to Learn more with you.

    Amir Mukhtar Ashrafi
    A student of Electronics
    Karachi .PK

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    • Parasuraman S

      October 5, 2017 at 7:54 am

      That is not wrong, dear! 100 marking on SMD resistor means, 10 with no zero to be added. The third digit indicates the number of zeroes to be added. For example, 101 indicates 100 Ohms. 102 indicates 1000 Ohms (1K) So on..... Kindly download and keep SMD codes from the open website and study. All the best!

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  8. Dr Tejas Gaydhankar

    October 12, 2017 at 1:17 pm

    Indeed a nice article... another one which ...I liked was about zeb ATX smps...Chinese tricking on resistor values.
    I have a same multi meter...but the resistor besides 10 ohms is burnt.. can't see the value in your pic. if u know the value.. please help.

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    • Parasuraman S

      October 16, 2017 at 7:13 am

      If you save the image and zoom it and see, it is clear. Anyhow, the next resistor value is 100 Ohms (101), the next one to that is 1.1K (112), and the next one is 16.9K (1692). Hope this helps!

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