An Ex-Employee Saved My Life, Says A Human Life Saver BPL Defibrillator Model DF2509
The power supply of this human life saver Defibrillator was rushed to me with the complaint that it got a shock for a change and conked off! Following is the picture of the SMPS:
Incidentally, it was my prudence that saved me from getting a shock, as the tank capacitor was found holding around 290V, which I discharged through a high watt resistor. We have to be very careful whenever we get such boards from anyone and what we should do always is to check the voltage in the tank capacitor and discharge it.
As you might all be aware, a Defibrillator is lifesaving equipment and should be in a ready to use condition 24 hours a day. But this unit suddenly conked off, upon which the biomedical technician opened it to know what went wrong. He mentioned that PWM IC was found burst and he could not make out the number from the shattered pieces. I told him to open a similar model lying in another department and let me know the number, which he did promptly. Let us have a look at the damage noticed and the one in a working unit:
The TOP227YN IC had burst. I removed it and combed the entire primary and secondary side of this double sided PCB, though the ring test showed healthy. I found another 600WATTS TRANSIENT VOLTAGE SUPPRESSOR Diode, P6KE200A dead short, picture of which is given in the last above. (I took four snaps and stitched them together). This diode is available in unidirectional and bidirectional modes.
The suffix ‘C’ indicates bidirectional, whereas ‘A’ indicates unidirectional. That’s why I said it was found short, as it was reading in both directions. Following is the circuit diagram of the PWM, which has this diode as a protector:
While combing the PCB, I had to remove some of the Mosfets and one side of many components like resistors and capacitors to check the value. This took several hours, as I had to use the Desoldering station to clean the holes before refitting the components or one side leads. After finishing that, I applied power through a series bulb, connecting a three wire AC, green colour ground of which is directly connected to the secondary ground. (This picture of the bottom side of PCB is what I gave in the beginning.) The battery charging output showed 13.43V, indicating that the SMPS was back to duty again. The board was delivered to the Biomedical Technician during my visit and he fit it in the Defib and shared a video. I am also giving a screen shot of it along with the voltage reading.
By this time, some of you might have raised your eye brows about the caption used. Yes, I was working in this great company, BPL, from 1976 to 1995, after which I joined the US based Medical Equipment manufacturing company taking over its Indian operation. So, while I worked on this product, it drove me back to my good old days, though I had nothing to do with its technical side. I was in the commercial department of the marketing section.
All these reasons sprouted utmost satisfactions impregnated with nostalgic memories, which got entry into the collection bag happily!
This article was prepared for you by Parasuraman Subramanian from India. He is 76 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 How Did This TV Even Switch On With All ELCOS Burst? – Strange Case Of AOC LED TV LE32V30M6-61
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