Beware Of These Fake PWM ICS
In this article you can learn (1) When to conclude a replacement PWM is fake (1) What to do when a replacement is not available (3) How to check SMPS using a module (4) How to connect a five wire Module
This computer Monitor belonged to the Hospital where I work and was brought to me with the complaint that they heard a loud noise and it went dead. I opened it and cleaned the inside assisted by my colleague and carried the display with boards to my home.
On check-up, I found that the TOP Series PWM IC was burst. I replaced the electrolytic capacitors and the PWM with TOP256EN, as I got this number from another technician friend, since the last number of burst IC could not be read. I also did a thorough retouch of solder points on the board.
But, no output came. I replaced the opto-coupler and TL431 and two electrolytic caps in the primary. Looked for any defective components in the primary and secondary and could not find any. So removed the IC and connected a three wire SMPS module, by connecting its red to B+ return from SMPS transformer primary and black wire to ground.
I left the Green without connecting as it is not required for testing. I got the desired outputs indicating that there was nothing wrong with the primary and secondary section.
This indicated that the primary switching section and secondary sections were ok. There could be something wrong with the feedback circuit, either in the primary or secondary or the new IC was fake. In order to make sure, I connected the following 5 wire Module:
Yellow to the source pin of Mosfet (B+return path from SMPS), Black to Hot ground, Red to Run DC diode, White to Opto pin 4, and Green to B+. I cut the track of Opto pin 3 and grounded it (Emitter of the photo transistor inside). When I switched on, the outputs were present and voltages ok.
So, connected the PS to Mother Board, which was already connected to the Panel and found it to be working. So it was a case of fake IC! (Experts to comment on this, please!)
Brought it back to Hospital and fit it inside the case. Here is a picture of the components replaced:
Mission successfully completed paving way for substantial satisfaction jumping into its bag!
This article was prepared for you by Parasuraman Subramanian from India. He is 72 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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You may check on his previous article on Dry Solder And Defective Capacitors Found In Philips AZ380/94