lcd television repair

Troubleshooting And Repairing Sylvania LD320SS8 LCD TV With Shutdown Problem

This is a common LCD TV that we see for repair. The failure symptom is almost always that the TV will turn on for just a moment, “digital television” is displayed in the lower right corner and then the TV shuts down and goes back into standby mode.

This type of failure is almost always caused by a power supply or inverter circuit failure in the majority of LCD TVs. Normally I would start by measuring output voltages from the power supply during the moment it is on to see if any are out of tolerance or missing especially the output to the inverter circuit, inspect the PCBs for solder connections with ring cracks and check the power supply secondary side filter capacitors for raised ESR and check the pico fuses and transformers on the in the inverter circuit etc.., but with this model I know that one of the HV transformers in the inverter circuit often develops an open secondary winding, typically it is the HV transformer at location T1100.

lcd tv high voltage transformer

The first thing I do with this model is check all the secondary windings to see if any have opened by measuring there resistance, an open winding will have an infinite resistance or if you are using a DMM you will get an O.L. (Over Limit or Open Loop) reading. Each one of the HV transformers in this model TV has 2 secondary windings.

lcd tv primary winding

While measuring the resistance I found that none of the secondary windings had opened, but what I did notice was that one of the secondary windings had a much lower resistance that then all the others I measured. All of the secondary windings had a resistance of between 522 and 527 ohms and the suspect secondary winding had a resistance of 495.4 ohms, about 30 ohms less than the rest. This was a very good indication that this secondary winding had shorted turns. This is what's great about testing the HV transformers in most LCD TVs, being able to compare the test results of one transformer against the others as typically only one of the HV transformers will go bad and it will be easily identified when tested and compared against the others.

lcd television transformer

lcd tv transformer

Upon closer inspection of the transformer with the shorted secondary winding the burned area of the secondary winding was noted as well, confirming without a doubt that the transformer was faulty and sure enough it was T1100, the transformer that we normally replace in this model but always for an open secondary winding but this time obviously the winding was shorted. Most likely what typically happens is the secondary coil shorts and then excess current is drawn as the resistance of the coil drops which in turn causes the coil to heat up and burn causing it to go open, but in this case the coil shorted and the TV shutdown before it had a chance to open.

lcd television high voltage transformer

lcd television transformer

After the HV transformer was replaced with a new one, part number LTZ2PC0MS008(substitute for 3PC0XB001) the TV turned on and functioned properly once again.

The LTZ2PC0MS008 can be found at Electronica USA along with many other electronics components.

Hopefully you all enjoy this article and special thanks to Jestine Yong for giving me the opportunity to do a guest post this month. Best wishes to all the ERG members. As always I can be contacted by emailing me

john@preher-tech.com

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