A Dead Tel/Fax Machine Repaired. Model: Sharp UX P100
This machine was brought to my shop by a friend of mine. It was completely dead. It was not sending or receiving and the phone in that machine was also dead. It was very obvious to me that it is a power supply problem. Let the repair begins.
I took the cover off which were only three screws on the bottom of that machine. The moment I took the cover off I found a black mark on the power board and that was my repair starting point. The fuse was open indicating a short in the power supply. The capacitor was already bad because I could see very clearly that it was bulged and one of its legs was already missing. It was 100uf/400 volts. I soldered that out and cleaned the board with a chemical liquid. I replaced that capacitor but did not power the machine because I want to make sure that all components are in good working order.
I have this meter in my shop that I love so much. It is the LOP/FBT tester. When placing the meter probes on the one of the capacitor legs and the collector of MOS N FET it should give me a full light bar but it did not. When this happens, either the capacitor, the MOS N FET or the secondary diodes of the power supply are bad. I know the capacitor is good because I just replaced it with a new one. I tested the MOS N FET and it was shorted out. The moment I disconnected the MOS N FET legs off, the light bars on my meter were restored indication a working power supply. It was K2972 and I replaced it right way with a same part number. I tested it again with my LOP/FBT meter and it gave me a full light.
I was now ready to power up the machine but before I did that, I connected a 100 watt light bulb to the main fuse connectors and powered up the machine. The light bulb came on bright then it went dim and that is an indication of that good working power supply. I replaced the light bulb with a 3.13 amp. Fuse and powered up the machine. The machine started to beep and the LCD screen on this machine came on. It worked perfectly.
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.