Three Wire Module Fixed In IMPEX 2.1 Multimedia Speaker System Model Musik Plus
This was brought by a technician from a faraway distance, with a request that the power supply section using SMD components be restored, as he was undergoing an eye treatment with restrictions on eye strain. The set was already opened and cleaned, saving my time on it. Let us see the board:
On my checking, I found that the fuse 3.15A was open. The rectifier diodes M7 were short. The Mosfet was already replaced by him, which I just removed and checked and found to be ok.
After replacing the fuse and M7 diodes, when I checked the primary with my Ring Tester, it showed healthy. After applying power, no output was coming, though the tank capacitor was getting the 300V DC. The voltage was standing steady even after disconnecting the power without getting drained, which is an indication that the Switching was not taking place. Discharged the capacitor and removed the SMD control IC and connected two wires (Red and Black) ignoring and neatly covering the green wire with tape.
Red wire was connected to the B+ return path from the SMPS primary and black was connected to the hot ground. This was not having any opto-coupler for feedback control. I kept the voltage adjusting potentiometer in the module at minimum. Then when I applied power, the output was ok. 
(You will find 110V marked on the module, as this was adjusted like that, which I changed to minimum). Then connected a USB and played a song, which was ok in the Subwoofer. He had not brought all the other speakers and I could not connect external speakers as the connectors were all different. But the front control and its remote were working very well and the voltage was steady even with the load.
I provided heat sink and fixed the module on the cabinet in a vacant place close to the primary of the supply and routed and fixed the wire properly. Mission accomplished resulting in satisfaction, which passed the qualification criteria to get entry into the bag! (LOL)
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
February 24, 2024 at 12:37 pm
This is totally over my head Maestro.
Please kindly explain what you believe the fault was and what the name of this ingenious work around is called.
Parasuraman S
February 25, 2024 at 7:01 pm
The Switching IC in the primary was the culprit. It had failed and no replacement was available. So a three wire SMPS module was used, ignoring the green wire. I have explained abou the use of this type of module in many of my previous articles and did not therefore repeat it. Many thanks!
Albert van Bemmelen
February 24, 2024 at 2:34 pm
Your expert fixes often go too quick and escape a clear explaining. Especially in these cases where again such a universal power module was used to replace a not working original pwm controller circuit. By leaving out the new changed circuit connections it doesn't help most readers, who never used such a module, in understanding how the modification was done. And a remark like "You will find 110V marked on the module, as this was adjusted like that, which I changed to minimum" then only adds to the confusion.
Parasuraman S
February 25, 2024 at 7:03 pm
Yes, your observation is very accurate. I too realised it after reading the article now. Shall take care! Many thanks for your expert comments!
Imoudu.O
February 25, 2024 at 4:52 am
Waiting for more explanation on these statements, 'You will find 110V marked......" Just has Albert.B observed.
Parasuraman S
February 25, 2024 at 7:05 pm
The module was set to give out 110V when I used it in a CRT TV. I used that only for such needs. But I had to use this module as I was not having a spare one at the time the technician came in. Many thanks for your observations and comments! Looks like I had got crowded with a lot of pending work when I prepared the article and missed even essential details. Anyhow, it shows that my article is being read in full, which is a solace! (LOL)
Yogesh Panchal
February 26, 2024 at 12:37 am
Good Job! Sir
Parasuraman S
February 27, 2024 at 9:58 am
Thanks, dear!
Mervin Binda
March 2, 2024 at 10:59 pm
nice job