ABW Multimeter Blown Apart
It’s easy to get it wrong. Sometimes, VERY wrong. That’s what happened to me when I filmed my very first YouTube video for my new channel. I was repairing a microwave oven and not realising the high voltages that they have, decided to test the high voltage transformer with my CAT2 rated multimeter.
To say things didn’t go according to plan is an understatement. There was a puff of smoke from my meter and after that it decided to just provide me with gibberish on the screen. Let me set the record straight – it was not the fault of the meter, it was user error. I was very upset as I had had this multimeter for many years and had just introduced it to the world of electronics, but it didn’t seem as excited as I was. I can now understand why……..
I did open up the back several times and was left with a blank expression on my face as I saw all the coloured components that refused to operate as they should. It went into the ‘too hard basket’. Step forward 5 years.
Now, I’m the first person to stick up my hand and tell you that I don’t know everything and am always keen to listen to others to guide me on my constant quest for knowledge. That being said, after all these years had passed, I had added to my knowledge base and surprised myself on many occasions with a successful repair.
The main thing to remember is – don’t get cocky. You can always learn something from others and just when you least expect it, you have forgotten some of the basics! Anyway, enough of that, I need to get back to my multimeter repair.
I had recently carried out a simple repair on a multimeter where someone (one of my students) had incorrectly replaced one of the sliding switches on the rotary dial and this had made the multimeter inoperable. Armed with this small success, I decided to have a look at several other multimeters that I had in my collection that didn’t work. The one that we are discussing, as well as several others that had been given to me by others that also did not work. (Stay tuned for further repairs)
The first thing I noticed about this ABW multimeter (which is identical to several other brands), was that the display worked. The main problem was that all the numbers, icons and features came up together, regardless of what position you had the rotary dial on.
That let me to thinking that firstly, the fuse was OK and the display was also working. It seemed to be some sort of processing issue.
Of course, the first thing to do in any diagnostic situation is to have a very good visual. I inspected the board and components carefully to look for dry solder joints, damaged components or evidence that the magic smoke had disappeared. Everything seemed OK, but I knew better!
I started a systematic testing of diodes, transistors and resistors. Nothing out of the ordinary. Time to raise the game. IC’s were next. For many years these little black boxes with legs resembling caterpillars mesmerised me and I felt that I had no right looking in their direction. Today was different! I had recently successfully repaired several units replacing faulty IC’s and was quietly gaining confidence in my chosen hobby.
I’ll be honest here – I have several of the same meter and so testing and comparing meter against meter showed a definite difference in readings. This led me to isolating the fault.
After waiting for some time to receive the items through the post, I went about carrying out the soldering process. I have replaced quite a few SMD’s with success and found the best way to replace these IC’s was to flood the area with solder and then heating that big blob would release all the IC’s legs at once.
I have now been introduced to a recently purchased hot air station and have been practicing removing components with hot air. This is another skill I have been able to learn.
The first IC to be replaced was a 27M2C OpAmp, which installed nicely. This gave me some practice to tackle the larger CD4053BM Multiplexer. After preparing the pads for new solder and adding flux, I carefully placed the tiny IC’s in position. Soldering one leg in place gave me the opportunity to realign them before completing the soldering.
At this point, I decided to test the operation of the multimeter and to my surprise, it worked! Not to be too sure of myself, I checked the operation of all the features and compared the readings with my good multimeter. They all checked out and were very close to the other meter’s readings. I even checked the frequency and duty cycle readings using a function generator I had made previously.
To say that I was impressed with the results was an understatement and it gave me a boost to my confidence and newly acquired diagnostic and repair skills.
The multimeter would live to measure another day! 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.
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Note: You can check out his previous repair article below: https://jestineyong.com/troubleshooting-and-repairing-benq-lcd-monitor-with-video/