calculator repair

Casio Calculator Repair with Thermal Printer 12 digit. Model: DR-T120

A customer in a nearby store brought his calculator that was completely dead. It was not an expensive one and I gave the customer a suggestion to buy a new one instead but he insisted on the repair for some reason. I never worked on a calculator before but it was time to learn something new and get paid for it.

calculator repair

I opened the cover and I could see the printed board with a lot of tiny SMD components. I checked for obvious burnt or shorted components but I found none.

calculator repair board

I powered up the machine and I could hear some humming coming out of the power supply. This power supply is not a usual one. It had multi voltages that are running throughout the calculator board. I could read, 18 volts going to the main capacitor which was by the way 6800uf/25 volts.

Since I was getting reading at the main capacitor that indicated everything in the primary section of the power supply is working fine.

calculator transformer

When I disconnected the main power I found out that the main capacitor was still holding the charge. That was an indication of a broken line or bad component somewhere on that board. The first thing I found was a bad diode that was shorted out and I replaced it. Since this diode was shorted out, this was my way of finding more shorted component along side of that diode. Sure enough on the same line, I found a Darlington transistor that was shorted as well. The part number on it was D1414D. I checked for other bad component and found none.

I powered the calculator and sure enough, it came back to life. I could calculate and also print on it as well. I was very glad to see it come to life and the customer was happy as well. He was very generous in his pay and I gave him a discount for any future repair.

This article was prepared for you by Waleed Rishmawi, one of our "Master Authors' and currently he is working in the Bethlehem area of Palestine repairing electrical and electronic equipment.

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