Sylvania LC320SLX No Power-Dead

[Protonus]

Re: Sylvania LC320SLX No Power-Dead

@kevinm34232 - did you ever fix this TV?

[budm]

Re: Sylvania LC320SLX No Power-Dead

Try lifting one leg of D639 ZENER, put D638 all other Diodes back in place and see if 33V is back up.

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

Of all the ones you had circled, D631 reads .0L immediatelly, the rest count up slowly until they read .0L which seems to be a pattern with my meter.

Basic question is since the 33v was missing is there a systematic approach for finding what may be loading that circuit like Ron said? Do I check all components in the schematic that I see connect with that D638 diode??

[budm]

Re: Sylvania LC320SLX No Power-Dead

D632 Cathode pad will read 0 Ohm which is what I expected as I explain on how it is used.
Same for D643 because the Cathode is connected to the winding of the transformer, which mean you will read 0 Ohm, that is the correct reading.
What do you read at the Cathode of the Diode as circled in red (no need to remove them for now)?

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

D632 and D643 are reading 0.00. So if D643 cathode should also read 0 ohms back to drawing block.

[budm]

Re: Sylvania LC320SLX No Power-Dead

"if I use pin 15 of T601 for ground and check for resistance I have 0.00 to the other 9 pins of transformer on secondary side" That reading is correct since DC resistance of the winding is very low Ohm.
"On page 40 Im using pin 15 of T601 for ground to the cathode pad of those diodes" So which one of the Diode Cathode is reading 0 Ohm, please note that D632 Cathode is connected to Pin 13 of the transformer winding (this Diode is used for Neagative power supply) so the Cathode side will read 0 Ohm.

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

On page 40 Im using pin 15 of T601 for ground to the cathode pad of those diodes, is that what you're asking? Im trying to check other components now to see if I can find something shorted but it's a little overwhelming.

Another note, if I use pin 15 of T601 for ground and check for resistance I have 0.00 to the other 9 pins of transformer on secondary side

[budm]

Re: Sylvania LC320SLX No Power-Dead

At which test point are you testing (the diode number Dxxx) so I can look up the sch?

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

With the Diode out put the meter in Ohm mode and check the resistance between Ground and the pad on the board where the Cathode (the banded side) of the Diode is attached to, then reverse the probe and take the reading at the same point again.
Best way to check the transistor and Diode is to test them out side the circuits.

I did this and have a 0.00 reading so this must be part of the problem. Do D632 and D643 have some component in common?

If I try to follow the schematic and what the 2 circuits have in common, what components can cause a short to ground?

[budm]

Re: Sylvania LC320SLX No Power-Dead

With the Diode out put the meter in Ohm mode and check the resistance between Ground and the pad on the board where the Cathode (the banded side) of the Diode is attached to, then reverse the probe and take the reading at the same point again.
Best way to check the transistor and Diode is to test them out side the circuits.

[Mr Bill]

Re: Sylvania LC320SLX No Power-Dead

0.480 and .0L. I just was wondering if that indicated a short on that circuit or if they were connected. Does D637 seem OK from above?

I've had a few even lower than .183 in curcuit but would be much higher out of circuit. I was hoping you would find something like in the picture. I can't comment on the 000 reading from the cathode end to ground but Bud M, Ron_cnet or others may be able to elaborate.

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

0.480 and .0L. I just was wondering if that indicated a short on that circuit or if they were connected. Does D637 seem OK from above?

[Mr Bill]

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.

What are the readings of those 2 diodes in circuit with your meter in "diode test mode"?

[kevinm34232]

Re: Sylvania LC320SLX No Power-Dead

The only diode I saw in circuit as reading same both ways was D637, I lifted one leg and get .0L and 0.183

[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.

[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.

[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

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.

[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

[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.