Desk Caller ID Telephone Repaired
I received this telephone that all the functions were dead. The wall out wire was the first thing that I replaced with a good one the sockets of the telephone wire was broken.
But telephone still is not functioning. I opened the box of machine and directly search for fuse/ filter of telephone the code of this fuse was TPA2000.
This fuse/filter does not show any reaction to multimeter even in fresh state.
I had in my stock P6KE200 from my last repair they are same as each other’s but still no voice in handset. After this the red led s of key board turned on to red lights this means voltages of the line are reaching to machine. I replaced the earphone hand set with a good one, yes the voice of beep beep line is coming now. This means the earphone of the telephone under test has problem.
Then I replaced the earphone capsule of telephone with a fresh one that I had in my stock but still the telephone has more problem! The key board is working and numbers are shown on the display LCD but not transmitting from the phone to the line and telephone center this means the main board of telephone has problem.
I resoldered all bad joint but still no progress then I start to check the electrolytic caps I found a bad biggest cap in the main, the legal value according the cap must be 1000 microfarad@10v but my cap tester read this 1444! And ESR at most must be 0.12 but I had 0.14 I replaced the cap, (this is the purifier electrolyte cap that is part of the power supply, of telephone) now the main board start to transmit dialing numbers, also I have to mention that on the main board of telephone zener diodes with different voltages are installed to regulate proper voltages for different part of machine when I push the button of HIGH PHONE to see if is working or not?
The speaker had no any voice this means somewhere something is disconnected may be? Or speaker itself has problem?, by following back from speaker by help of the beep tool of multi I found out that one of the 22 wire of flat cable was disconnected from pcb, just the first wire that was belongs to speaker line was broken, the kind manufacturer of the telephone printed the pcb just in front of each wires of flat cable one by one and mentioned the job of each wires like spk or tone, and etc….
This made my job much easier by the help of the pin of one unused resistor and soldering iron I reconnect the wire no1 of the flat to the pcb, I desolder the pin hole of the first wire and by the help of solder sucker I cleaned the hole number one on the pcb then I cut about one centimeter of resistor pin and soldered on pcb , by scraping the plastic of flat by a sharp blade I made it ready the rest of wire no. 1 to solder with the installed pin .after that speaker starts to produce whistling!!
This means that Audio frequencies are reaching to the speaker but speaker does not have enough abilities to produce the normal sound for human ear! The speaker must be 8 ohms according to the attached label on the back of the speaker but my multi read this lower!
This means some wire windings of speaker must be shorted! I replaced the speaker with a good one. Now telephone completely is working with no problem and strongly returned to services. And a few dollars were the cost of this repair.
Note: In these kind of the Chinese telephone the wires between the boards are very short due to saving the wire and make the final product more economical but in repair job these wires must be extended and more wires must be added to the original wires Unless otherwise repair is not possible and testing the boards are difficult, but same number wire must be used.
NOTE: I took the photo of telephone in the darkness to show the beauty of red and green lights color of the LEDs on the panel after telephone was rescued.
This article was prepared for you by Mr Beh from Iran
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