element eldft551 not turning on

[cashkennedy]

Re: element eldft551 not turning on

If Budm doesnt even really know what kind of protection the section that leads to DA4 provides can i just remove DA4 and see if i still am getting shutdown signal?

[tom66]

Re: element eldft551 not turning on

I can't see a problem as long as you only do it briefly and you disconnect all loads. If the output voltage skyrockets it might blow the output caps...!

[cashkennedy]

Re: element eldft551 not turning on

The over voltage protection is handled by ZA1 and ZA2 would not be disabled by just removing DA4 would it? From what i understand theres 2 differnt checks feeding into the same opto. Then again im not 100% sure how ZA1 and ZA2 sense overvoltage. Are those zeners specific ones that only let current past if its over 26v and 14v respectively or something? or are SMD zeners all the same? Im fairly certain the actual power supply stably creates 12v and 5v as they both reach a very stable reading for the 1-2 seconds they turn on, the 24v on the other hand barely reaches 23.8 when the power supply shuts it off / so I dont have any way to know for sure it wouldnt have climbed further / this could be what the overvoltage is detecting, and possibly it is seeing a higher voltage faster then my multimeter, and so thinks it got to high.

[budm]

Re: element eldft551 not turning on

Since thground terminal of the power supply board is monitoring if the 24v supply is being connected to the load or not by sening the ground pin which eventualy gorund when the inverter is connected, that is the only thing I can think of why it has that circuit sensing at the ground point of the 24V. For the 24V sensing of through the Zener Diode to work, the ground return of the 24V power supply has to be completed by having the inverter connected. So what you can do is to connect the 24V ground retturn pin to the 12V gorund return pin and have 24V small lamp connected to the 24V output and see if it will work.I have a feeling that thecomparator circuit is the one that is triggering the shutdown since the sensing of the ground return of the 24V is an open circuit, not grounded out, basically it wants to shutdown if the load is not connected, in this case the gorund of the circuit is compeleted when it is connected to the inverter board, then that sensing line to the comparator is grounded out.

[budm]

Re: element eldft551 not turning on

Ok I just look at that comparator section again. Have the TV plugged in but NOT turn on if you check the DC voltage at the Anodes of DA4 (check both of them) when the cable is not connected between the power supply and the inverter board, then hook up the inverter, see if the voltage at the anodes change state.
Notes: that comparator circuit does not look like it is drawn correctly, the bottom one cannot change state if it is hooked up as shown, the output at pin 7 of UF4A will always be high or low dependS on the voltage divider network of R33~36 values. I would also try lifting Diode DA4 after you verify the voltage at both Anodes of DA4.

[cashkennedy]

Re: element eldft551 not turning on

Do 2 12v bulbs in series work as a 24v load? Incadescents are fairly resistant to temporary over-voltages anyways right? I was also considering just forcing the inverters on with a long wire / resistor to the 5vsb.

[cashkennedy]

Re: element eldft551 not turning on

Edit: wait up here, I might have been reading the wrong side of the opto (1 side should be 5v im guessing as its connected to Vref. gonna go retest quickly / hard to see the traces while the sun is setting.




I was testing for voltage at the anodes of da4, tried power off / cable connected and disconnected / and finally power on but neither had any voltage vs the secondarys ground (screw hole / all the grounds in the connectors)

So I figured let me test it closer to the opto. I don't have any voltage there either vs the same ground (screw hole so on...)

So there is no voltage on 1 side of the opto, but 5.1v on the other side... Im guessing I have a short somewhere between d31 and the opto.

Tell me if this sounds bogus / did these measurements with the new multimeter / did some tests with it and auto ranging is a little trippy / so just set it at 00.00 V range... I might also be using the wrong ground, not sure.

[cashkennedy]

Re: element eldft551 not turning on

K I retested , currently what im getting is nothing on the secondary of the opto, on the primary the vref side is 5v , and the important side(the emitter I guess) is .61 vdc (so that might not be enough to trigger an error in itself). now after d31 I get ~5v at q18 I get 5v on collector, 4v on the base, and 5v at the emitter... so maybe c53 or r30 is shorted? or theres something going on here that I don't understand.

[tom66]

Re: element eldft551 not turning on

If the opto failed OPEN, the OVP would never trigger. So it can't be open, IMO.

[cashkennedy]

Re: element eldft551 not turning on

So q18 has 3 diode readings

red on emitter > black on collector .750V
red on emitter > black on base .655V
red on collector > black on base .659

Im pretty sure that's my bad part, thoughts?

Maybe this is a pnp transistor? (do I tell that just by the arrow pointing towards base instead of away?)
so that would mean what I called emitter was really collector and what I called collector was really emitter on all the readings above

Also explains why I see 4.1 v on the shutdown pin , its basically 5v minus .750v diode

[cashkennedy]

Re: element eldft551 not turning on

I pulled q18 off (used some wick), put board back on without any grounds connecting the screw holes, and the power board on some cardboard. plugged it in, turned it on and got some steady sparking / light output / magical smoke , the sparking might have been coming from the TCON not 100% sure. The inverters did come on / set stays on. I freaked out unplugged everything and made sure the carboard wasn't burning, but everything looked good as new... so I installed board properly with screws and all , and got a millisecond spark when connecting the set from the tcon (not sure if just a reflection...?) ... but it went away, so I started testing set, and it turns on / and turns off fine, and inverters light up, but I don't have any sound or picture, just backlight and on off control are working...


So idk if something else blew, or is the sparking was just the flux burning off? or maybe sparking was related to me not connecting a ground to power supply? could the tcon have fried cause of there not being a dc ground to frame? there was a AC ground from my extension cord connected to the TV at all times though. The sparks could have been from a bulb in the center and just bright enough to go through the metal ? most of the glow when it first happened was from the center of the bulbs / not really the tcon or the power supply...

[cashkennedy]

Re: element eldft551 not turning on

The piece of carboard I had the power supply on had some cellophane on the back / the cellophane shorted a few lvds wires together / burnt the connector out / destroyed wire and tcon as far as I can tell.

The LVDS on this is fairly unique to the set (with the extra separate wires / connectors on the mainboard) so Ill probably need a true replacement , not just make due with stealing one off a similar cmo panel set.

http://www.ebay.com/itm/ELEMENT-ELGF...item416c9d04e0 might have to buy that , still looking.

[budm]

Re: element eldft551 not turning on

Well, right now I am completely confused by what you have done.

[cashkennedy]

Re: element eldft551 not turning on

I was pretty sure q18 was bad as it had 3 diode readings (see readings about 5 posts ago), I removed q18, power supply works great now , all voltages stable.

Only down side is that I started the set with cellophane over the lvds cable , and it shorted the cable, that burned a hole in the lvds and the connector on the tcon.

If this seems unlikely / and you think something else related to be removing q16 / starting the tv with out the power supply well grounded might have cause the tcon connector to fry, then tell me . I sure as hell don't want to buy a tcon and lvds cable (looks like ill be spending around 30 total) just to have them go bad again.

[cashkennedy]

Re: element eldft551 not turning on

The short story on how I isolated Q18 and decided to test it really carefully is > that I got .6 volts right after the opto, but 4.1 v on the shutdown pin of the IC, so knew the error was inbetween. Realized there was basically 5V on all 3 sides of Q18 so decided to test it carefully.

I just went back and tested the voltage of all the LVDS outputs from the mainboard with the set on, and the red wires on the LVDS read 12vDC, and 0v for all the black wires , and .5-2v on the LVDS pairs. So hopefully that's a good sign that the fried LVDS cable wasn't from the actual signal being transmited, but hopefully from the cellphane shorting it.

[budm]

Re: element eldft551 not turning on

OK, so right now Q18 is removed, the shutdown is no longer in the circuit. Since you are reading 0.7 between E and C which is not right, it should show OL on the meter.
It is PNP transistor, so the E is connected to the 5V,, so the Base voltage should be about 0.6~0.7V lower than the Emitter. So if you do have 0.6 between E and B, that transistor is on so the C will have about 5V also to feed the Diode.
On the opto the LED side, if it is activate, you should have about 1.8VDC on the 2 pin of the LED side.
What you can so is to put the q18 and then short the two pins of the OTPO LED side, that will turn off the Opto for sure, if you still get 5V at the Collector of Q18, then you on the right track that Q18 is bad.

[retiredcaps]

Re: element eldft551 not turning on

(hopefully that's just sarcasm about my meter)

It is obvious that my attempt at some humour to help you has failed. Sarcasm is not part of my personality.

I was assuming primary = AC , secondary = DC when I took the measurement , but that's not a good rule at all lol.

However, the subtext looks like it made you think it through and find a resolution. As I write this, I'm 40 posts behind in this thread alone since I last logged in so I have some catching up to do.

PS. In general, we don't ask people to do a lot of AC measurements for the purposes of this forum. In fact, I think budm is the only regular who asks for any kind of AC measurement and that is usually on the big filter cap like in this example

https://www.badcaps.net/forum/showpo...3&postcount=31

[cashkennedy]

Re: element eldft551 not turning on

Yeah ive learned a lot on this set. Thanks for all the help so far! Schematics make a world of difference. I also found a great pdf explaining the different implementations of PFC that's teaching me a lot.

The new multimeter is pretty fly, Im sure most of the auxiliary functions are fairly inaccurate, and the COM wire seems to get loose if I swing around the wires a bunch / but that's what you tend to get when you buy something 1/10th of the price of fluke. I trust the simple voltage and resitance measurements it makes to be close enough to not cause significant problems (within 2%).

There a bunch of 50-55" sets in my area (mostly plasmas) in the 125-150 range. Im trying to talk some of them down to $100. Hopefully it will lead to some good profits, cause guns are starting to be plentiful in the stores around here / and starting to crave more. What are you willing to pay for faulty 50, and 55's? (question is to tom66 and others, not to budm obviously who works for free

[retiredcaps]

Re: element eldft551 not turning on

1/10th of the price of fluke.

Check your local pawn shop as per this thread ...

https://www.badcaps.net/forum/showthread.php?t=24239

https://www.badcaps.net/forum/showthread.php?t=26191

[cashkennedy]

Re: element eldft551 not turning on

No cheap flukes on my local craigslist for more than a few seconds. I don't really go to pawn shops except when ffl transferring guns. I don't really see an advantage to getting a "simple" fluke that is meant for a specific purpose and only does the main basic tests, when cheap meters can do the basics just fine (within 2%). True RMS meters are only help with current, and we don't really need that around this forum. Infact we could all use the $5.00 harbor freight multimeter for basically everything. Obviously that meter is a piece of crap physical quality wise (I own one, and ive had to resolder the connectors) , the next up models at harbor freight (both have clamps) don't do capacitors , the 4th highest has a horrible screen that goes bad, and finally the best they sell, the one I got, doesn't really have any big down sides, other then that the included dB meter is trash. Plus im starting to enjoy the range selection a lot more then constantly rotating the dial.