Sylvania LC320SLX No Power-Dead

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

So can you help me understand what I should or could be looking for on my own? Does it seem to be a short on the secondary side, etc? Earlier I asked if lifting cahtode leg of D638 would isolate that AL33v circuit from D638 which is the source, is that true? Why are my other voltages low aswell like Q601?

Ughh I was just checking Q601 and touched 2 pins now I don't have the 163v there. This TV was almost free, it was all about trying to troubleshoot the problem. Should we just move on to the next one?

[RON_CET]

Re: Sylvania LC320SLX No Power-Dead

kevin in theory by lifting the leg of D638 if there was something loading down that line our 33v should have come back up on just the cathode leg of diode we lifted,now from the rest of you standby voltages like the al13v thats low course now that the 2 pins were touch over on Q601 that transistor could be bad now

[RON_CET]

Re: Sylvania LC320SLX No Power-Dead

look on the positive side you have learned a lot of troubleshooting techniques and that complete board is also very inexpensive if your wanting to just replace the board

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

Ok.. so since the 33v didn't come up when we lifted D638 any guesses? I'd be happy to keep going just don't wanna waste everyone's time for a crappy TV, Id have to order some parts first of course

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

Yes thank you all for the help on this one I agree. Hate to give up but yes learned a lot. Have 3 or 4 more sitting here waiting anyways!

[budm]

Re: Sylvania LC320SLX No Power-Dead

If you look at the diagram, D638 is the rectifier (It gets its AC from transformer pin 11) that feeds filter cap C638 and the clamping Zener Diode D639. If you lift the leg D638 then for sure you will not have the 33V. I would look real close at that Zener D639, and that filter cap.
I do not understand why you expect to see 33v when the D638 is not in place.
Unless I am missing something.

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

Sorry Bud as Im not educated enough in the function and how all of the components work together, I'm just trying to keep up with what you guys ask and follow instructions. Ideally for my own knowledge I'd love to have the same model working TV sitting next to this one to be able to compare readings to give you. However that said I appreciate any insight. I believe C638 tested good and D639 aswell on my DMM diode setting.

[RON_CET]

Re: Sylvania LC320SLX No Power-Dead

it does get it's Ac input from pin 11 T601 but if you lift cathode side of D638 you should see the 33 volt dc come up on the cathode,D639 would not prevent the 33 volts unless it was leaky or shorted and he did say D639 was good,be same thing if we had cold solder joint on the pad but at the leg we had the 33volts

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

Question I see some voltage protect circuits in the SM is there any chance that the problem is elsewhere and shutting down the voltages we are looking for? I just googled the model # and came up with this:
http://www.fixya.com/support/t102899...vania_lc320slx

[Mr Bill]

Re: Sylvania LC320SLX No Power-Dead

I believe i read a post a while back that if one inverter transformer was bad it would shut the tv down. But, the tv would start to turn on (led would flash). You have no led at all. You did check all the diodes right? I'm only asking because it was mentioned very early in this thread but i don't see whether you confirmed this. The few sylvania's and emersons i've repaired all have had 1 bad diode. The one slyvaina LC420SS8 had no standby led. It was a shorted diode.

What is the board number on your power supply. I have a 32" emerson power supply in the basement.

[RON_CET]

Re: Sylvania LC320SLX No Power-Dead

those 3 resistors in that link are in the power supply startup for the backlight inverter,if those were giving you the problem of protect3 shutdown which is monitored @ pin3 of connector cn1001 first thing you would notice would be the power led on front of set would first go to red stanby then after you hit power it would go green and the protect3 line would go to 3.3 volts once the protect3 line goes to 0 volts from a inverter power supply issue then set would shutdown,from what i gathered you had no power at all to set not even a stanby led indication?

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

I checked all diodes and resistors on the primary side, it's a big board and wasn't sure if it was practical to lift every resistor and diode on the secondary side without being instructed.. This is my board:
http://www.shopjimmy.com/sylvania-a9...unit-board.htm

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

Yes Ron correct everything was dead just was wondering.

[Mr Bill]

Re: Sylvania LC320SLX No Power-Dead

This was the diode that was shorted on my last sylvania that was completly dead. I never lifted any of the diodes. I checked them in circuit and if it read 000 then i removed to verify.

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

Im gonna check some diodes out of curiosity, I get weird readings in circuit some seem ok some are questionable. Is there a trick to checking them in circuit? Some read like they should with a reading one way and .0L the other, some read both ways.

[Mr Bill]

Re: Sylvania LC320SLX No Power-Dead

you should get something one way and OL the other. Don't freak out if you see some diodes that read .120 one way and OL the other. If it's shorted you'll know it. It'll be 000 both ways or darn close. Focus on the bigger diodes. All the tvs i've fixed have all been the larger ones.

Good Luck

[budm]

Re: Sylvania LC320SLX No Power-Dead

You will not see 33Vdc at the Cathode of the Diode since there is no cap to charge up to the peak of AC. You can build the circuit and test out that theory, all you are getting is the high frequency at the only half of the cycle coming through.
How do you think you get about 170Vdc when you rectify 120VAC, 120 X 1.414 =169.68VDC.

[RON_CET]

Re: Sylvania LC320SLX No Power-Dead

sometimes depending on how there connected in circuit in order to get a correct reading you should remove or lift one side to make sure nothing in the associated circuitry is giving you a whacky reading

[budm]

Re: Sylvania LC320SLX No Power-Dead

It is just a simple half wave rectifier set up with filter cap, nothing special at all.
Take a 120 to 6V transformer, attach a diode to one leg of the transformer, take a DC meter one probe to Catode, another probe to the other lead of the transformer and see what DC you get at the Cathode, then attach a 10uf or so to the Cathode and another end of the transformer, I will bet you will not see 8.48VDC without the cap.

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

My meter doesnt seem to do well checking diodes in circuit get a lot of readings both ways.

But not sure if this is correct but I started checking cathode side of diodes to ground, and 2 diodes (D632 and D643) have a reading of 0.00.