Dick Smith LOPT/FBT tester repair.
This is an old tester that I have in my shop. I bought this tester on EBay when I first opened the shop about 12 years ago. Today as I was testing a laptop power adapter, I did a terrible mistake and I shorted out the meter. Seems like the main capacitor was not discharged as I expected and the moment I did the connections on board, the power indicator went out indication a dead tester.
I opened the meter cover and the first thing that I saw was a black burnt on a 1k resistor. I soldered it out and tested and it was an open resistor. I replaced it with a new part but that did not bring my meter to life.
I stared checking the entire component on that board. As you can see in the photo, most of the component there are resistors and all of them checked fine. I continued with my testing and could not find any bad components.
There are two IC’s on that board and the only way I can test them is by checking voltages on them or with the oscilloscope. The power supply here is four AAA battery sizes which come to total of 6 volt reaching the main small capacitor. I did the voltage testing on the first IC part number LM393N and there was voltages reaching that IC and 3.17 coming out on all the legs of that IC which indicated something wrong. I did not have a replacement part for it in my shop so I ordered from a local store just about 20 minutes away from my shop. I had to wait till the next day to get it. There was another IC part number CD4015BE on that board. To be on the safe side, I ordered that IC as well.
I got the two IC’s in the morning and the moment I installed the LM393 on board, the meter came to life. That put a smile on my face because I was feeling guilty about breaking this meter. It was silly mistake that caused me time and money.
My lesson for the day, we are humans and we do mistakes, we should learn from our mistakes and move on. ALWAYS DISCHAGE CAPACITORS BEFORE WORKING ON ANY EQUPMENT.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment. Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
By the way if you have any good repair article that you want me to publish in this blog please do contact me HERE.
(20)Dislikes
(3)
4 Comments
Leave a Reply
shihab kably
July 26, 2013 at 7:08 pm
test devices are our weapons in this field and it is important to learn how to take care for them .thanks for sharing this experience
Waleed Rishmawi
July 27, 2013 at 4:32 pm
you are welcome Shihab. tools and knowledge gos hand in hand in the repair field.
teddux
October 31, 2017 at 1:20 am
That LM393 is a common problem in these units.
I couldn't find a replacement; so, modded a LM339N in situ...
If each time you depress the ON switch and the LED's count-up, the second "Shift Register" I.C.2 is Okay. "Part A" of I.C. 1 is bad.
I just got through repairing mine that sat w/ batteries - leaked/ damaged for years.
Installed new brighter LED's, also.
Drilled hole in top of case for power supply when needed. No more internal batteries for mine!
Already made a new board but it will wait in the case for another time.
jai
February 7, 2020 at 10:39 pm
Good job Waleed.