REPAIRING AND NOT THROWING AWAY

Richtige Fernseher haben Röhren!

Richtige Fernseher haben Röhren!

In Brief: On this site you will find pictures and technical information about Service Modes, Circuit Diagrams, Firmware Update procedure, Disassemble procedure, Universal remote control set-up codes, Troubleshooting and more....

If you go into the profession, you will obtain or have access to a variety of tech tips databases HERE IT IS Master Electronics Repair !.

These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.
As always, when you get stuck, checking out a tech-tips database may quickly identify your problem and solution.In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts.

Happy repairing!
Today, the West is headed for the abyss. For the ultimate fate of our disposable society is for that society itself to be disposed of. And this will happen sooner, rather than later.

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..............The bitterness of poor quality is remembered long after the sweetness of todays funny gadgets low price has faded from memory........ . . . . . .....
Don't forget the past, the end of the world is upon us! Pretty soon it will all turn to dust!

©2010, 2011, 2012, 2013, 2014 Frank Sharp - You do not have permission to copy photos and words from this blog, and any content may be never used it for auctions or commercial purposes, however feel free to post anything you see here with a courtesy link back, btw a link to the original post here , is mandatory.
All posts are presented here for informative, historical and educative purposes as applicable within fair use. NOTHING HERE IS FOR SALE !

Tuesday, 19 February 2019

LG 37LH55 POWER SUPPLY TROUBLESHOOTING

LG 37LH55 POWER SUPPLY TROUBLE SHOOTING


    AC should not be applied at any time while adding resistors or unplugging connectors as damage to circuit boards might occur.
[A] The SMPS PWB 'Must' be producing STBY 5V on either pin 7,8,9 or 10 [5V].  If this voltage is not produced SMPS PWB is defective.  There is no need to continue with next test.
[B] Unplug  P700 on the main PWB and P203 to the ballast.
Add a 19K resistors between [5V Standby] pin 7,8,9 or 10 and pin-2 [PWR].  Apply AC.  This will turn On the power supply.
  • Check that the 24V and 12V power supplies are turned ON, P201 (24V pins 17 & 18) (12V Pins 13 & 14) and  24V to the Ballast P203 Pins 1-5.
  • Remove AC Power.  Reinsert the plug P203 to the ballast.
Continue if the above test is OK.  Leave original 10K resistor in place.
  • Add an other 10K resistor between 5V pin 7,8,9 or 10, and pin 20 [INV On]
Unplug the small ribbon connector  CN-1.  [This floats P-DIM].
  • Apply AC power.  This simulates a Power ON and Back light command.
  • If back light is normal:  If all is normal the back light should turn ON
  • If back light is abnormal:  Recheck connector P203 and confirm  24V on pins 105.  If low, or missing , use diode mode to check the 24V line on Ballast connector CN 1.  If low, this indicates a shorted output FET.
  • If Open, check Ballast fuse, possible open.  
  • Confirm the INV On/Off line P203 pin-10 is going to 3V
  • Confirm Pin-3 of CN-1 has >2V.  If not, need to add 3V by adding a 10K resistor from 5V_ST to pin -3 of CN-1.  Back light should light.
Remove AC power
  • Check the connections to the back lights.  'Do Not' check with these when AC is applied as they can carry [1.2Kv each].