Failed SMPS Switching IC Bypassed In PANASONIC LED TV Model TH-23A403DX
This TV was brought by a regular customer with the complaint of not getting on. After thorough cleaning of inside, when I checked, I saw bulged capacitors in the secondary side.
I replaced the bulged capacitors first. Another capacitor had leaked too spilling over the electrolyte over to adjacent IC and components. After replacing all the electrolytic capacitors, I cleaned the area thoroughly using IPA. Then applied power and did not find any output. The tank capacitor was remaining fully charged to over 325V DC and did not drop on switch off quickly, which itself is an indication of absence of switching of the primary.
I discharged the capacitor and removed the Mosfet fit on a heat sink to locate the Switching IC and connecting circuits underneath it. The six pin small SMD switching IC had a marking of NMP and 3GR by its side on the top and FG underneath it:
As there was no datasheet available for this IC and symptoms showed not switching, I checked all the components for any short, open or difference in value and did not find any. The ring test showed healthy reading indicating that there was no short in the secondary. The optocoupler was checked using two multimeters, one digital and another analogue.
Using the X1 in ohms range, checked the pins 1 & 2, while keeping the digital multimeter probes to the secondary side, in ohms range. It showed a few ohms when the voltage was applied in the primary by the analogue multimeter, confirming that the opto was working very well. Then I connected a three wire module to the primary, by ignoring its green wire and connecting the red to the B+ return from the SMPS transformer and the black to hot earth. Kindly see the following link for detailed description of the use of this three wire module: https://jestineyong.com/cracked-unknown-pwm-replaced-by-universal-module-in-pressure-monitor-smps/
The output was present when power was given indicating that the switching IC was faulty. As a replacement was not available in the market, I decided to provide a 5-24 Board in order to revive the power supply. First let us have a look at the three wire module connected to the PCB:
Connection of a 5-24 Board was well explained by me in yet another article, link of which is provided below:
As mentioned in the article, I lifted pin 3 & 4 of opto from the combo board (hot end side pins) and connected two wires to it. Then removed the opto from the 5-24 Board and connected the wires from the opto of the combo board to the 3 & 4 points in the 5-24 Board. Then connected the other wires of the module to respective places (Black to hot ground, Red to B+ return from the SMPS transformer) Thus the primary switching was bypassed to this module while maintaining the original SMPS secondary section and switching-regulatory-feedback from it, intact in the combo board.
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I fixed the Mosfet of the module to the heat sink. Let us have a look at this arrangement:
The TV came on when powered up and the output of 12V was stable. There were minor lines on the screen, which did not hinder the viewing. The customer was fully aware of this problem and wanted to use it to the best possible extent, as a replacement panel was not available in the market.
Mission got accomplished deriving satisfaction which got gulped by the collection bag without any hesitation!
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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Mark J
February 15, 2026 at 4:06 am
Parasuraman great article good troubleshooting. Thank you for sharing.
Parasuraman S
February 15, 2026 at 10:49 am
Many thanks, dear Mark!
Lewis
February 17, 2026 at 8:06 pm
Hello Parasuraman.
It was very interesting reading this repair as I think I have seen this technique by another engineer on You tube using 1 Str 5 pin modification. Thank you very much.
Parasuraman S
February 18, 2026 at 4:59 pm
Many thanks for your comments and reference!
MP
February 15, 2026 at 8:39 am
As I started reading the article, I almost got disiniterested until I read the all too familiar words to the effect, "i used IPA". Otherwise its quite unlike you to hurriedly scratch on the surface with little disregard to detail as you narrate a repair issue. The NMP SMD IC doesnt look to me like an effective high frequency SMPS switch for a 23 inch LED tv. A more robbust-looking-like-transistor mosfet looks far more reliable though and hence a better replacement. The power module incorperates the reassuring much needed transistor based mosfet. I know of a crt tv that has been working without a hitch for, exceeding 3 years, with a power module. Now the repaired Panasonic tv here only calls for 30 watts to operate, so I will ignore whats written at the back and find out whatever the cause for it to get warm are, I mean abnormal warmth. As I write this, please every one of you pray for my family so that God gives us strength, courage and wisdom as we prepare to burry our departed mum. MP=MUYKIT. God bless.
Parasuraman S
February 15, 2026 at 2:23 pm
Heartfelt condolences! RIP - Many thanks for finding time to post a detailed comment!
Yogesh Panchal
February 15, 2026 at 3:46 pm
MP,
My sincere condolences to you and your family on the loss of your mum. May she rest in peace, and may you find strength during this time.
Waleed Rishmawi
February 15, 2026 at 7:24 pm
MP: praying for you in this difficult time. May the Holy Spirit be with you all with a special comforting… praying for you all.
Tito Kanshulu
February 19, 2026 at 6:55 pm
May the soul of your mom rest in eternal peace
Yogesh Panchal
February 15, 2026 at 4:33 pm
Sir,
The
NMP 36R FG component is an LD7536R Green-Mode PWM Controller. & here is Link for Circuit diagram.
https://elektrotanya.com/panasonic_th-23a403dx_chassis_ms82p-ap.pdf/download.html
Parasuraman S
February 15, 2026 at 6:49 pm
Vow! How Did you manage to get it? Many thanks for your comments and info.
Yogesh Panchal
February 16, 2026 at 12:59 am
Sir,
You can't rely on SMD codes as standard, as companies are marking their own codes to create confusion and maintain their monopoly.better way to trace the pins in circuit connectivity to other components & try to understand working of that particular pin.
Parasuraman S
February 18, 2026 at 5:00 pm
Yes, I do have an application that can help. Many thanks, dear Yogesh Bai!
Albert van Bemmelen
February 15, 2026 at 4:46 pm
I also searched invain for that NMP pwm SMD IC datasheet. But also searched for the code 36R instead of the mentioned 3GR. Sadly it never showed up as being a matching pwm chip. Thanks for another repair showing the use of universal PWM modules.
Parasuraman S
February 15, 2026 at 6:49 pm
Many thanks for your comments and feedback!
Tito Kanshulu
February 19, 2026 at 7:00 pm
NMP are difficult to find. The only solution is to get them from junk boards or to do a modification with these available pmw modules
Parasuraman S
February 20, 2026 at 5:47 pm
Yes, let us be practical! Many thanks for your comments!