LC-60LE550U No Power

[m4a2t0t]

When I check Z7001 (I cant remember what its called. Is it a thermistor?)I am seeing 123V when measured across both terminals and it also reads about 2M ohm. Thats bad right? How do I determine the replacement value. The board has zero voltage except across the input and the fuse.

Thanks

[nomoresonys]

Re: LC-60LE550U No Power

thats your metal oxide varistor, just measured the one on my bench, its about 1 m ohm, the other similar looking component that sometimes gets confused with it is an ntc which is a thermistor, those are about 10 ohms.

[nomoresonys]

Re: LC-60LE550U No Power

yours looks to be ok.

[nomoresonys]

Re: LC-60LE550U No Power

to test you just measure resistance, thats ohm scale, high reading varistor is good, low ohms means its bad, ALL ohm readings are done with tv UNPLUGGED from power.

[m4a2t0t]

Re: LC-60LE550U No Power

OK. thanks for the info.. Its measuring 1.6M ohm

Any suggestions of what else to check?

[nomoresonys]

Re: LC-60LE550U No Power

what exactly are the symptoms, when you try to turn it on?

[m4a2t0t]

Re: LC-60LE550U No Power

No power at all. The front light doesnt even turn on anymore.

Isnt the low side of the PSU isolated from the high side with those opto isolators? If I use the low side ground as a reference point I get no voltages anywhere on the low side. If I use the neutral of the high side I read AC voltages on the low side. I must be doing something wrong.

[lotas]

Re: LC-60LE550U No Power

The hot side (high voltage) has its own ground, the cold side has its own ground, and they are isolated from each other.

[R_J]

Re: LC-60LE550U No Power

The first thing to check is the standby voltage. Check the voltage ACROSS C7950B, If there is o volts then it is likely IC7903 is not working, check the resistance of R7900, it should be a couple ohms, if it is open, IC7903 is likely shored.

[m4a2t0t]

Re: LC-60LE550U No Power

Voltage across C7950B is 4.98
R7900 - 3 ohms

I rechecked the output pins and every pin except pin 8 is 0V or something like .030 V. Pin 8 is 4.98.

[R_J]

Re: LC-60LE550U No Power

There are actually 24 pins (two rows) on the PD plug, pin 15 (not 8) is BU5V (5v standby)
Pin 14 is PS_ON, You need to check the voltage on this pin, this pin turns the power supply on and off.

[m4a2t0t]

Re: LC-60LE550U No Power

Oh, I thought pin 2 was to the right of pin 1. There is 0V at pin 14. If grounding it turns on the PSU like a PC then that doesn't work either.

[Davi.p]

Re: LC-60LE550U No Power

Sharp TV don't have an high signal on the PS-ON pin at open circuit, you must jump bu5v to PS-ON

[m4a2t0t]

Re: LC-60LE550U No Power

Ok I wired ps-on to 5v and nothing changed except pin 5 and 7 are now rapidly swinging from about 2v to 8v. I do see 1.6v on pin 13 now.

[Davi.p]

Re: LC-60LE550U No Power

probably there's a short on secondary, try measuring the pins of the KIA regulator if there is one, is probably under the heatsink near the PD connector, 4 pins to220 package, eventually removing it to test the rest..

[R_J]

Re: LC-60LE550U No Power

Ok I wired ps-on to 5v and nothing changed except pin 5 and 7 are now rapidly swinging from about 2v to 8v. I do see 1.6v on pin 13 now.

Did you disconnect the cable between the main board and power supply before shorting pin15 to pin14 first? if not the main may be holding down that PS_ON pin
Check that there are no shorted diodes in the secondary like D7131, D7130 etc. if there are no shorts, next check to see if your PFC circuit is working, To do this check the voltage ACROSS C7800A or C7800B, In standby this voltage should be around 165VDC, when the ps is turned ON, this voltage should be around 385VDC and steady.

[m4a2t0t]

Re: LC-60LE550U No Power

How do you test it? There is a KIA378 under the heatsink next to the connector. I get the varying voltage on the DC input, Output is 0V, and the on/off pin is 0v. If I check the resistance from ground to the input pin on the KIA I get 350 ohms.

[m4a2t0t]

Re: LC-60LE550U No Power

Did you disconnect the cable between the main board and power supply before shorting pin15 to pin14 first? if not the main may be holding down that PS_ON pin
Check that there are no shorted diodes in the secondary like D7131, D7130 etc. if there are no shorts, next check to see if your PFC circuit is working, To do this check the voltage ACROSS C7800A or C7800B, In standby this voltage should be around 165VDC, when the ps is turned ON, this voltage should be around 385VDC and steady.

I didnt remove the cable. I will check all of this now

[Diah]

Re: LC-60LE550U No Power

take out the PWB and put it on the table to run stand alone test... so you have access to down side.

[m4a2t0t]

Re: LC-60LE550U No Power

I removed the cable and when I start it the input pin of the KIA goes to 13.8v, no output. The unit does make a faint noise now when I turn it on.

All the diodes on the secondary side seem good.

Voltage across C7800A and B is .001 in stby and .198V after i turn it on. I coulda sworn it was reading different yesterday.

What voltage is the rectifier bridge supposed to output? If I measure from a primary heatsink to the + pin im getting 14V. From bottom to top on the rectifier. - 0v, 63V, 63V, + 14V