A Simple Fix To A Dead Electronic Scale Brought It Back to Life
A friend of mine brought this dead scale to be repaired. He said this scale was sitting in the storage room for a long time and when there was a need for it, the scale did not power on.
While the customer waits in the shop,
I powered the power supply and as seen in the photo, the green stand power LED light did not come on indicating a fault in it.
Before cutting open the power supply to find the fault I powered the scale using my bench power supply and as seen in the photo, the AC charging sign came on indicating a working electronic scale.
It was not easy cutting through the power supply plastic case but finally it was done and I could see a lot of dry soldering joints. I re solder all these joints but that did not bring the power supply to life.
There were 310 DC volts at the main capacitor and when disconnected it, the capacitor was discharging fine.
I have seen such fault before and if I am not mistaken I think the power supply was not powering because the main output cable was shorted causing the power supply not to provide any voltage to the output points.
I de soldered the main output cable and right away the LED of the power supply came on and I could read a 24 volts about the output pins.
I cut off the main output plug and tested it for continuity; it was ok. It seems like the whole cable was shorted and needed a replacement.
I used a new thicker cable as seen in the photo but kept the main power plug since I do not have the same size in the shop. I soldered it, isolated it with electrical tape and plugged it in the electronic scale.
As expected the scale came on and it was working according to specs.
The customer came for pick up and he was happy with the result. He tested it by weighing himself; he approved the accuracy of it (He weighed about 70 kilos and that what showed in the display).
Mission Accomplished.
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.
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Note: You can check his previous article on A Welding Machine With Overheating Issue Repaired
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Parasuraman S
November 4, 2023 at 1:38 pm
Though the fix was easy, finding the fault requires a lot of expertise! Good job and thanks for sharing!
Waleed Rishmawi
November 4, 2023 at 3:51 pm
Parasuraman:I appreciate your kind words. have a blessed day my friend.
YOGESH PANCHAL
November 4, 2023 at 4:35 pm
Goof Job! Waleed.
Waleed Rishmawi
November 5, 2023 at 12:13 am
Yogesh:I am sure it is a typing mistake when wrote goof job.. lol have a blessed day.
Yogesh Panchal
November 13, 2023 at 4:04 pm
Ha ha......
Albert van Bemmelen
November 4, 2023 at 4:49 pm
Luckily this power supply had a decent pwm circuit that protected its components by preventing any too high short-circuit current.
Waleed Rishmawi
November 5, 2023 at 12:16 am
Albert: yes you are right otherwise we would have a mess in there. Have a blessed day.
Tito Kanshulu
November 5, 2023 at 4:14 pm
Good job Waleed. We have learnt something
Waleed Rishmawi
November 5, 2023 at 9:17 pm
Tito: thanks man. I am glad you did. Have a blessed day