Don't Miss


Digitor Multimeter Repair

By on April 2, 2020

 

 

 

 

 

 

 

Some repairs are simple.

digitor multimeter repair

Some repairs are created difficult if someone else has been there before you, attempted an unsuccessful repair or have actually created the problem that you now face. Most times if someone has damaged a component or done something wrong, it is a very rare thing that they put up their hand and own it.

At the college were I teach, we have a range of multimeters that the students can use during classes. However, occasionally the classes may be bigger and there may not be enough meters for everyone to have one. That’s where the main issue with this multimeter repair began.

When I teach anything electrical or electronic, I drag around a trolley with multiple storage containers. I have years’ worth of bits of wire, experiments I have made, examples of faulty components, testing equipment I have developed, etc. I carry one of my personal multimeters with me (that’s right I have more than one – well over twenty in fact 🙂 ), and on this particular day, we didn’t have enough meters for the students, so I lent him mine…….

The first rule of Electronics is: You do not lend you multimeter to students.

The second rule of Electronics is: You do not lend you multimeter to students.

I was teaching the students how to test for voltage, resistance and current. I instructed them on the importance of moving the positive lead when testing for current. I also explained that if they did blow a fuse, not to panic and then showed them how to disassemble the multimeter and replace a fuse.

At the end of the day, all the meters were put pack in the store and mine was placed back in my hallowed electrical storage system. All seemed fine. Until….next time when I was showing the class a feature of my particular multimeter. The screen appeared, but nothing made sense and no readings could be taken. To say I was put out was an understatement.

I nestled my cherished multimeter, but I couldn’t bring it back to life. This would require something more drastic!

Naturally, I assumed that the magic smoke had disappeared and that there would be remnants of a charred circuit board when I disassembled the meter. Unfortunately, I didn’t have a schematic that I could refer to and as a hobbyist, I am always questioning my levels of skills. But I soldiered on, thinking that I could logically work through the components one by one and find the complex fault had had obliterated my precious meter.

I started with fuses. But looking back, there was no need to do that as I had all features on the screen, so it must have had power. Next I started a systematic testing of all diodes and transistors. I headed into the deep end! I found 2 transistors that had a dead short across the terminals, so I felt I had discovered the fault.

digitor multimeter repair and fix

As I removed the component off the board and tested it, I discovered that it was working fine. After closer inspection of the board, I noticed 2 things – firstly that the 2 outer legs of the ‘transistor’ were tied together on the track and secondly, it wasn’t a transistor at all! It was a CM431 current shunt regulator.

multimeter circuit board repair

After finding a testing procedure using a 1KΩ resistor, the regulator proved to be working correctly, outputting 2.5 volts.

magnify glass for repair

Maybe the IC’s were faulty…..perhaps I should replace those.

But, before I did that, I took a step back. I smelt the circuit board. If there were burnt components, it is not unusual for the board to have a horrible burnt smell. No smell. What was I missing? As I said, I have several meters, so I disassemble one of my other ones and started to compare one with the other.

I didn’t have to dig far as after a good visual, I suspected that I had found the fault. When I removed the rotary dials, I noticed that the little switch contact points were in different locations. Surely it couldn’t be this simple – after all the testing I had done!

how to repair multimeter

As you can see in the photo, the sliding contact had been fitted in the wrong spot. I must admit, it is easy to do and I have done it on a number of occasions, but fortunately, I have found my mistake before reassembling the meter.

So what actually may have happened? Remember I said that I had taught the students how to replace a fuse in the multimeter if they happened to blow one? This is when they perhaps dropped the rotary switch or one of the sliding contacts and then installed it in the wrong position. Easily done and to be quite honest, not really their fault. As you can see on the dial, there are 2 positions that the sliding contact can go back on. Perhaps this is for a more advanced multimeter with more features, but using the same basic construction.

Whatever the case, I could rest easy knowing that I had another multimeter that I could use.

how to fix digitor mutlimeter

I learned several lessons in this repair, firstly:

The first rule of Electronics is: You do not lend you multimeter to students.

The second rule of Electronics is: You do not lend you multimeter to students.

Secondly, that not everything has to be a complex repair and taking a step back to access the basics, even though you thought you had covered them all is a good idea. And lastly…..it doesn’t hurt to have a spare identical multimeter to check your testing against!




If you are interested in this repair, you can see a video on my channel following the link below:

This article was prepared for you by Mark Rabone from Australia.

Please give a support by clicking  on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.

P.S- Do you know of any your friends who would benefit from this content that you are reading now? If so, forward this website to your friends or you can invite your friends to subscribe to my newsletter for free in this Link.

Note: You can check out his previous repair article below:

https://jestineyong.com/ingelen-trv111-am-portable-radio-repair-with-video/

 

Likes(77)Dislikes(0)

15 Comments

  1. Albert van Bemmelen

    April 2, 2020 at 1:16 pm

    Your warning is clear! And in case one of the sliding contacts got missing after one of the students opened the multimeter we just buy another cheaper DMM and use one of those mostly matching copper sliders to replace the missing one in our more expensive digital meter. I therefore normally never lend out my expensive electronic instruments to anyone who has not got any good knowledge of our instruments and who values the importance of our equipment! Same goes for other things like Blurays or DVDs because it happened more than once that they were completely destroyed by the person who I lend them to.

    Likes(5)Dislikes(0)
    • Mark

      April 2, 2020 at 4:35 pm

      Thanks Albert,
      I don't know what I was thinking!
      I normally don't hand out my precious multimeters. They must have caught me in a moment of weakness...
      Good idea buying a cheap multimeter for the sliding contacts. I'll keep that in mind 🙂

      Likes(3)Dislikes(0)
  2. Gassan Ali

    April 2, 2020 at 1:26 pm

    Great work! I downloaded this videos on YouTube. Keep more electronics repair coming. It's really helpful that you make the videos.

    Likes(1)Dislikes(0)
    • Mark

      April 2, 2020 at 4:36 pm

      Hey Gassan,
      I have another multimeter repair coming up soon. This was a little more complex, but fortunately, I was able to rescue it 🙂

      Likes(1)Dislikes(0)
  3. Parasuraman S

    April 2, 2020 at 2:14 pm

    Vow! What a suspense thriller article! It looked like a godzilla in the beginning and turned out to be a tamed cat! A big relief! You have very aptly and correctly pictured the psychology of a technician, especially a hobbyist like me, and made me go through it as though I was doing the troubleshooting and repair! Well done!

    Likes(1)Dislikes(0)
  4. Mark

    April 2, 2020 at 4:39 pm

    Thanks Parasuraman,
    This helped me to repair another multimeter, which will be in a future article/video. I am constantly learning and sometimes I forget to just take a breath and step back and start again with the diagnosis.
    It really helps to have another meter to compare when you don't have a schematic.

    Likes(3)Dislikes(0)
  5. Robert Calk Jr.

    April 2, 2020 at 6:11 pm

    Good job, Mark! The manufacturer wants you to throw the DMM away and buy a new one.

    Likes(2)Dislikes(0)
    • Mark

      April 2, 2020 at 9:00 pm

      Hey Robert,
      There doesn't seem to be too many repair videos on multimeters, so I am enjoying the learning experience & hopefully be able to share with others along the way 🙂

      Likes(2)Dislikes(0)
  6. reza

    April 2, 2020 at 10:06 pm

    Hi Mark
    hanks for sharing your experience

    Likes(1)Dislikes(0)
    • Mark

      April 3, 2020 at 11:14 am

      You are welcome Reza!

      Likes(0)Dislikes(0)
  7. reza

    April 2, 2020 at 10:10 pm

    Hi Mrak
    Thank u for sharing your experiance

    Likes(1)Dislikes(0)
  8. Imoudu Onwumah

    April 9, 2020 at 6:00 pm

    Good repair from experience,however maybe you can help me out.I have a model uni-t ut39A+ which 400omh,4k,40k ohms are not functioning but all other modes are functioning. It's a 4 months old dmm.Pls advice me what to do base on your repair experience.

    Thanks

    Likes(0)Dislikes(0)
    • Mark

      April 10, 2020 at 1:41 pm

      Hey Imoudu,
      I guess start with the basics.
      Are your fuses & battery OK? Are there any dry solder joints? Did it happen after you took a specific measurement? Is the rotary dial contacting properly?

      It is very difficult to make a suggestion without a schematic, but find where the rotary dial is positioned when in the resistance mode and work back from there.

      Likes(0)Dislikes(0)
  9. Imoudu Onwumah

    April 12, 2020 at 4:13 am

    Thanks Mark,I will check all those areas.Have a nice day.

    Likes(0)Dislikes(0)
  10. Humberto

    April 15, 2020 at 10:41 am

    Thanks Mark, for sharing your experiencies. By the way, I was Electronic Teacher at school many years ago.

    Likes(0)Dislikes(0)

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Free Report