Malfunction Of LM324 SMD IC Caused No Output In V-GUARD Voltage Stabilizer Model VG50
This voltage stabilizer was brought to me by my neighbor saying that it was getting on but no output came even after the three minutes’ delay. I opened the unit and found the inside very clean and neat. It consisted of a control board with LM324 SMD IC, two relays, two SMD transistors and one through-hole transistor. Let us have a look:
I applied power and checked whether the voltage was reaching the IC pin No.4 . 6V was present out of the 17.5V generated in the secondary because of a Zener SMD diode (Z1). I replaced all the three electrolytic capacitors as a routine on such complaints. 470/40V, 100/25V and 47/25V. The third cap was the timing control cap.
I checked the voltage build up across this cap when the unit was powered and noticed that around 3.79V was coming but not going down or going up, one of which should have been the design to operate the relay. I checked all the components on the board and did not find anything wrong. On consultation with my techie friends, they told me to replace the LM324 as it can become defective for no apparent reasons. I removed the IC using blower and replaced with a new one, cleaned the board and retouched the portions that got dry in the process and applied power and waited for three minutes to get the following result:
As I had kept the leads of the cap long for measurement of the voltage across it, I watched it getting drained to around 3.43V, upon which the relay got operated and green LED lit, indicating that output relay was triggered. As there were no defective components in the board such as a leaky cap, value changed resistor etc.
I have no idea why the LM324 failed, which according to the techie group, was a common fault in this stabilizer. I cut the extra leads of the cap and reassembled the unit and gave a bulb as load and switched on. The bulb got on after a delay of three minutes:
I went to my neighbor’s house, fixed the unit to his Fridge and waited for it to get on, collected my charges, exchanged some niceties and returned.
Mission accomplished with satisfaction and new learning getting added to the collection!
This article was prepared for you by Parasuraman Subramanian from India. He is 74 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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Tayo
October 4, 2025 at 10:57 am
Good to have friends in high places! This ICs are impossible to diagnose and you would have been going around in circles (thinking it was good) if your friend didnt advise you to replace it. I had a similar (but larger) IC saga sort of like you had here. I checked everything and checked it twice. After 2 weeks everyone involved threw in the towel and concluded it was the IC at fault. It was specialized so I had to just order a whole new board but it was a good experience.
Parasuraman S
October 4, 2025 at 1:34 pm
Yes, sometimes troubleshooting drives us crazy! Many thanks for your comments and sharing your experiences!
Albert van Bemmelen
October 4, 2025 at 6:11 pm
The LM324 is a quad OP-AMP IC consisting out of four high gain amplifiers. And they easily can be tested in simple to make Opamp tester circuits. However the smd chip size being not DIP or DIL size requires us to use a smd to DIP adapter. How to make such adapter that is not available anywhere is explained in my old article here:
And Opamp testers are now cheaply available and also can easily be made from standard parts. Just like testers that test the special Comparator opapms (which normally can't be tested in normal only Opamp testers!).
Parasuraman S
October 4, 2025 at 6:51 pm
Many thanks for your expert comments and very useful link, which I refreshed and read my comments too, dear Albert!
Mark J
October 5, 2025 at 2:36 am
Parasuraman once again great job on the repair.
Parasuraman S
October 5, 2025 at 12:03 pm
Many thanks, dear Mark!
Waleed Rishmawi
October 6, 2025 at 3:55 pm
hi, never encourtered such a device but I leared something today. thanks for sharing and have a blessed day
Parasuraman S
October 6, 2025 at 6:14 pm
Many thanks, dear friend!
Yogesh Panchal
October 8, 2025 at 7:24 pm
Good Job! Sir
Parasuraman S
October 9, 2025 at 3:44 pm
Thanks!