Instant Make Vertical IC Checker
As a CRT TV under repair was causing problems in the vertical section inspite of the best trouble shooting methods employed, the doubt was naturally on the IC itself. But even when I replaced it, the problem could not be solved. Fake ICs are available in the market and I thought a jig to test it would be appropriate. So, I built a circuit to check the LA78040 outside without involving the high voltage circuits and yoke, which had a risk of failure of other components too in the process of repeated check-ups.
I assembled the circuit in a common board, with a bridge rectifier and capacitor so that I can connect the secondary of a 24V Transformer. I used IC sockets for inserting the IC so that I need not have to solder it each time. A 7805 IC supplied the 5V required at PIN 7. The yoke coil at pin 5 was ignored.
After checking and rechecking that all connections were ok, I applied power and connected an Oscilloscope to its output and got a good wave form. Then an idea stuck me that a Vertical IC is just an amplifier and audio could work, if I connect a speaker on the output. I fed audio to its input and got an amplified signal at the output on the speaker. This is something many technicians might not be aware of! The following picture is a screen shot of the video I took.
This test helped me conclude that the IC under test was good enough and something else was wrong in the CRT TV and I continued my search for the problem in it. (Note: Since the test was only for a few seconds, the 24V to the input of 7805 did not matter!)
Mission of a different kind accomplished with utmost satisfaction that got added to its collection bag!
This article was prepared for you by Parasuraman Subramanian from India. He is 70 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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