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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Albert van Bemmelen
October 27, 2020 at 7:16 pm
You probably needed to test quite a few of these LA78040 Vertical TV IC amplifiers in the past to construct this special tester. But if you want to do this for every other analogue IC that exists in the CRT TV world, you got a lot of unfinished work left to do! (lol)
I suppose that is what differentiates it from the ease of use of most universal digital IC testers.
Parasuraman S
October 27, 2020 at 11:38 pm
Yes, I agree. LA78040 is a common vertical IC and testing that off the board will help me troubleshoot a problem faster. I enjoyed the laughter side of your comment! Many thanks!
Joseph Gomez
October 27, 2020 at 7:50 pm
Very Creative and amazing. I have followed many of your repairs and rebuilds and have always been impressed. Learnt much from your postings. Thanks.
ps : Also Learnt much from many of the other Gurus on this forum
Parasuraman S
October 27, 2020 at 11:39 pm
This is a forum in which all of us learn many things from each other! Thanks to Jestine Yong, who is taking a lot of trouble in maintaining it to help us!
Eric Rice
October 28, 2020 at 8:59 am
Good job as always!
Thanks,
Eric R.
Parasuraman S
October 28, 2020 at 8:25 pm
Many thanks!
Humberto
October 28, 2020 at 12:42 pm
Wow! What a test circuit for this vertical IC! You are a Master.
Parasuraman S
October 28, 2020 at 8:26 pm
Many thanks, dear!