Mystery Monger Monitor – LG MODEL W1953-TE PF
This monitor which was serviced by me by replacing bulged capacitors in November, 2024 did a revisit in January, 2025 with the complaint that it was dead. Earlier the complaint was dull display though the capacitors were found bulged, about which I have already written a report and it is in the queue. That was one mystery and this is yet another.
On opening and checking the power supply, the 12V and 5V were present. But on switch on, absolutely nothing happened.
When I checked up the voltages, the P-on (Enable) for backlight was just coming as a flash and stopping. Then I thought the problem could be in the backlight, as this was an LCD monitor. I focused on the back light issue and downloaded its datasheet.
The 12V was present on pin 18. I used the ring tester and checked the secondary of the booster transformer and found it to be ok. Then I used another LCD Monitor full boards and connected the LCD lights and found the lights turning on indicating that the lamps were ok. Then I wanted to turn on the backlight without connecting the mother board. I connected a 10K resistor from 12V to enable pin 2. Then tried. But backlight did not light up. Then followed a link provided by my techie friends, which I am providing below. The language is Hindi.
In it, he said to cut the track of pin 9 and connect a 47K resistor to the ground. But that also did not turn the lamp on and I therefore removed the Mosfet IC and checked. The Mosfet IC was having one N-Channel and one P-Channel:
When I checked the duo Mosfet using my analogue multimeter in X1 range, both Mosfets were found to be working and it got on and off using the usual methods to turn it on. If anyone wants to know how to check it, there are plenty of videos in YouTube. Then why was it not getting on?
Anyhow I ordered for replacement ICs which I might get in a couple of days. Then turned my attention to the mother board. First I cut the 12V supply to the LCD driver to disable it. From my experience, usually the monitor panel should show indication of power on. This was a touch type panel and I touched the panel several times by even using different fingers and hands. But nothing woke up the monitor. Then I checked the IC number and downloaded its datasheet.
Then used my oscilloscope to check the crystal of the µcontroller IC and found it to be working. The voltages were also normal:
Then checked the clock and data pulses that go to the touch control IC. Found these also present. But the output from the IC was remaining stagnant when I tried touching the panel again and again using different fingers and hands.
I removed the connectors and applied lubrication oil on both sides; i.e, mother board and the slave board. But nothing changed the mutant monitor. Then I tried touching the board from behind instead of from the front. Then, the mysterious monger monitor woke up!
Then I wanted to check the backlight after connecting the working mother board. So, I re-connected the 12V supply, replaced the Mosfet and removed the de-protection resistor and made everything like how it was before. There again, the backlight was on and the display was also damn good!
I allowed the monitor to be on for several hours before putting the covers back. Let us have look at the mother board of this mystery monger monitor and the result:
The monitor was responding to the touch from the front also! Mission accomplished mysteriously though satisfaction had enough reasons to get entry to the bag! The ICs ordered will get added to my inventory for future use!
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.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
P.S-If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!
You may check on his previous article on Bypass Surgery Done In SAMSUNG LED TV Model UA32T4450AKLXL
(34)Dislikes
(0)
12 Comments
Leave a Reply
Albert van Bemmelen
August 2, 2025 at 7:26 pm
This was a mysterious monitor repair which leaves questions on what had changed that got it working? But glad that you nevertheless got it working (again)!
About using an oscilloscope to check the crystal of the µcontroller IC, I recently noticed that the EMC that was radiated by my Hantek DSO 2D15 oscilloscope while checking a DCF module. It caused unacceptable electromagnetic interference with the DCF transmission. Which showed in erratic pulses inbetween the 200mS and 100mS pulses that normally should appear once in each second. So my guess is that the Hantek scope is not adequately shielded from transmitting these unwanted emissions!
Parasuraman S
August 2, 2025 at 9:08 pm
Yes, oscilloscopes do cause interference unless properly shielded. Many thanks for your expert comments, dear Albert! That mystery got solved much later during its re-visit, which I am covering by a new article on it.
tree
August 2, 2025 at 8:02 pm
Great job, sir.
Parasuraman S
August 2, 2025 at 9:09 pm
Many thanks!
stv
August 3, 2025 at 5:16 pm
maybe a dry joint u missed?
Parasuraman S
August 4, 2025 at 3:53 pm
No. That was retouched already. Thanks!
Waleed Rishmawi
August 2, 2025 at 10:01 pm
Sometimes reseating flex cables after cleaning connecters can do magic I have seen it happen before. Thanks for sharing
Parasuraman S
August 3, 2025 at 10:22 am
Yes, I do agree! Many thanks, dear friend!
Mark J
August 3, 2025 at 7:46 am
Parasuraman great article. I like that your articles are always thorough. Thank you for sharing.
Parasuraman S
August 3, 2025 at 10:23 am
Many thanks, dear Mark!
Yogesh Panchal
August 3, 2025 at 5:35 pm
Good Job! Sir,
If you didn't have spare motherboard, this would be difficult job.
Parasuraman S
August 4, 2025 at 3:52 pm
Yes, luckily I had! Many thanks!