A Five Wire STR Module Did Not Work In This AOC LCD Monitor Model TFT15W60PS
This Monitor was serviced using a 5 wire module and I had submitted my report which may please be studied before reading this article:
https://jestineyong.com/beware-of-these-fake-pwm-ics/
As you could perhaps see, I had solved the fake IC problem by connecting a 5 Wire STR Module and the Monitor worked very well for almost one and half years before brought in dead condition. On opening and checking the Monitor, which was clean inside, being used in an AC environment, I detected that the 5V and 14.5V outputs were missing.
I looked for any defective components in the primary and secondary and could not find any. 325-330V DC was present across the tank capacitor, when power was applied, but switching was not taking place. I checked the Run DC and found that around 9V was present, but it was not stable and was getting dropped. I checked the module and found all components were good. Then it could definitely be a case of STR failure and therefore replaced it with a new one and fit it in place:
When I applied power and checked the outputs using a Digital Multimer, the output of 5V and 14.5V (showed around 17V because there was no load of the backlight) was ok. So, I connected the mother board which was already connected to the panel. But the Monitor did not get on. I was wondering why and rechecked the voltages again using the Digital Multimeter and found these to be ok. Then I checked the Run DC and found it to be around 11.6V but it did not look like steady. Thinking that electrolytic capacitors could be the culprits, I checked ESR and found these to be slightly out of range. Anyhow, I replaced all the electrolytic capacitors including the Tank Capacitor and did a retouch of the board. But nothing worked and the Monitor did not get on though voltages were ok.
Then I remembered Jestine Yong’s instructions in his books about the use of Analogue Multimeter, which is quicker in its responses. I checked the 5 Volt using the Analogue Multimeter and found it to be slightly oscillating (vibrating). So, that was the reason! I checked the Run DC also using the same Analogue Multimeter and found the same phenomenon there also! So, I assumed it could be due to the oscillation filter fixed capacitor, 152/2KV and replaced it. It was found to be out of range too. But the monitor did not get on and the oscillation was still there. On a further investigation, I noticed that the oscillation was prominent only when the Mother Board was connected. So, I replaced the four electrolytic capacitors on that board too. But that also did not bring the necessary result. Then, I was wondering as to what could be wrong, as a similar 5 wire module indeed worked last time and failed only now. Then it stuck me that perhaps the current drawn could have got increased due to ageing of the LED backlights.
So, the power drawn was beyond the range of the 5 wire module. That is when I thought of using the 4 wire 5-24 Universal SMPS Board instead of this. (As I have covered usage of this board in a few articles before, I am not repeating them here) So, I removed the STR module and wired the 5-24 Board, which had Red, Black, Yellow and Blue Wires. Red was to be given to the point where primary B+ return through the SMPS transformer. Black was for Hot ground. The Yellow and Blue wires were the outputs which were supposed to be given to the secondary section of the transformer and a potentiometer in the board to be adjusted to get the desired voltage. But what I did was lifting the 3 & 4 pins of the opto-coupler in the Board and connecting these two wires from those points on the board to the opto-coupler of the PS board of the Monitor. In this way, a grafting would take place, by which switching and voltage regulation would be as designed in the original circuit, using the bypass board instead of its own. Let us have a look at the picture:
This time there was no vibration of the needle of Analogue Multimeter and the Monitor worked very well. As I could not fix the module within the PS board on top, I removed the heat sink plate and straightened the two soldering lugs and fixed the Mosfet on that with the original screw duly providing a pad. Then placed it on the bottom metal cover and fixed it there with another screw from behind. Let us have a look at the pictures to follow this better:
I fed the signal from my Micro-VGA Test Generator and allowed the Monitor to be in on condition for several hours and made sure that there was no failure.
I ensured that fresh conductive metal tapes were put on the silver foil stickers of the panel case as I had to peel them again which made the sticker lose its stickiness.
This is very important and I am providing a picture of that too before concluding this article:
Mission accomplished resulting in greater satisfaction getting added to the bag!
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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Albert van Bemmelen
December 22, 2024 at 7:17 pm
The Master of using universal smps power modules strikes again!
I hope to follow your successful replacing story too in the near future since I have not used any of these modules in any repair yet.
Parasuraman S
December 22, 2024 at 10:24 pm
These are some special methods used by expert techie friends here and I get a good lot of guidance and support from them, without which I will be nowhere! Thanks for your valuable comments, dear Albert!
Bill G
December 22, 2024 at 11:07 pm
Thank you for your innovative articles on using substitute power supplies when the OEM SMPS breaks down. Could you please describe how do you know where to break into the OEM circuit card with the four or five wires from the replacement? In other words, how do you know where to connect the new wires and cut the old traces?
Yogesh Panchal
December 23, 2024 at 12:00 am
Good Job! Sir,
Have you tried these type of power Module in ATX SMPS used in PC.
Waleed Rishmawi
December 23, 2024 at 3:00 am
Interesting repair, I never encountered such issue and never had the chance to use such modules. I have learned something new today. Thanks and have a blessed day
Imoudu.O
December 23, 2024 at 5:45 am
I didn't get you right where you finally solder blue and yellow wires of str, why did the use of new 5 wire module failed this time...aging in stock?
Mark J
December 23, 2024 at 8:47 am
Parasuraman another great article and repair.