element eldft551 not turning on

[cashkennedy]

Re: element eldft551 not turning on

No, unfortunately at home I have my 7 function clamp on multimeter ($12)
in my condo I have the 7 function cheapo 5 dollar one
maybe I should splurge and get the 11 function one ($20) but the reviews say that one has a horrible screen that fails... I need another multimeter for home though cause I keep leaving mine at work / and my neighbors always borrowing mine...

these are all from
http://www.harborfreight.com/catalog...t?q=multimeter

Ill attach new pictures in a minute.

[cashkennedy]

Re: element eldft551 not turning on

Took forever to figure out a way to get no glare. Finally propped the board up vertically in a extremely bright room. Hopefully you can make do with 4 pics, if you really need 10 pics like you showed I can go take some more *sigh*...

BTW clamp on part of the multimeter is worthless. I didn't buy it for electronics obviously, but for AC repair and what not , but the clamp only measures current and not voltage ...

[tom66]

Re: element eldft551 not turning on

Well, of course the clamp only measures current. The definition of a voltage is a potential difference between two points, how would you design something with a single clamp to do that?

AC current is still useful though I prefer clamp with both AC and DC.

[cashkennedy]

Re: element eldft551 not turning on

Yep, you described the downside better then me, it also is a really finicky clap, not only do you need the wires 90 degrees from the clip (which is understandable) but you also have to try a lot of different positions inside the clamp / like move it around and you get all kinds of varying readings ...

Theres a $44 multimeter also at harbor freight, that one looks like a winner all around, its basically a knock off fluke 87 with auto ranging and everything. I think I qualify as using mine enough to warrant the price, Im practically using mine on 3 projects a day... all my stuff has been dieing on me... had 2 computers in a row go bad on me for caps in the power supply / had replacement all on hand though

[cashkennedy]

Re: element eldft551 not turning on

Any luck? or knowledge gleaned from the more detailed pics?

If your still having trouble making parts out I can take 10 smaller shots with a digital camera instead of that phone.

Board is laid out horribly... cant see a p/n on a single damn one of the FET's and other to-220 parts.

[cashkennedy]

Re: element eldft551 not turning on

From what I can discern from the secondary the large transformer creates 12v only then there are 3 identical power diodes (correct term?) mounted to the heatsink: 2 power diodes for the 24v section , 1 for the 12v .

The smaller transformer leads to a power diode that creates 1 voltage follower by a dc regular (d452a) that makes it the 5v .

[budm]

Re: element eldft551 not turning on

I have not have a chance to look at the new pictures yet.

[tom66]

Re: element eldft551 not turning on

Forgot to link to the MLT199 schematic. Got the CD yesterday and have already got about 1,100 schematics up. Still, I haven't hit the 10GB threshold, yet!

http://www.tgohome.com/ServiceManual...&Search=Submit

[budm]

Re: element eldft551 not turning on

That is great to be able to get the diagram, thanks TOM.
OK, on page 3 top left corner of the page, there are VCC1 (for PFC IC, which is working), and the VCC2 for the 12V/24V SMPS IC UA4 pin 12 on page 2, check and see if you have 12V or more on VCC2.

[tom66]

Re: element eldft551 not turning on

I hope it's the right one. Shame that there are no component values on it.

[cashkennedy]

Re: element eldft551 not turning on

Thank you Tom! Schematic isn't perfect (a few components are marked differently / probably a few versions of this power supply / with different spatial requirements / so numbered a few components differently) but its definitely close enough to count on.

I think weve isolated the problem down a lot > the vcc2 reads 11.5 - 12 ish VAC against cause ground when the set is just plugged in , but when you turn the set on (LED lit blue) then it drops down to 9 VAC. I assume it should stay steady at 12 if things were working as designed? There is no "lag" time between pressing the power button and it decreasing by the way, the millisecond I press the power button it drops down to 9 vac.

[retiredcaps]

Re: element eldft551 not turning on

I think weve isolated the problem down a lot > the vcc2 reads 11.5 - 12 ish VAC against cause ground when the set is just plugged in , but when you turn the set on (LED lit blue) then it drops down to 9 VAC.

Wow, your HF multimeters need replacing if they are reporting VAC when they should be measuring DC voltage on the secondary side of the PS.

[cashkennedy]

Re: element eldft551 not turning on

The measurements he requested are on the primary side, and I can test VAC or VDC if I want with my multimeter...(hopefully that's just sarcasm about my meter) but if they wanted VDC I can retest for that, Its really late at night / I just worked 12 hours and yeah now that I think about it VAC doesn't make a lot of sense as these chips are after the bridge rectifier, I was assuming primary = AC , secondary = DC when I took the measurement , but that's not a good rule at all lol.

> tv off : vcc2 = 9.1 VDC
> tv on : vcc2 = 6.75 VDC (first second or two of "on" was around 6.35 VDC, then stabilized at 6.75)

At least I specified VAC vs VDC so there was no ambiguity

I am buying the $44 dollar multimeter tomorrow (fluke 87 knock off) , clipped the 20% off 1 item coupon from my sunday paper , so should be around $39 after tax. Found a 50" plasma and 42" LCD and a 50" lcd(Samsung in the bad cap class action suit) all in my area so might be fixing a bunch more big ticket TV's...

[cashkennedy]

Re: element eldft551 not turning on

That IC that were testing the VCC on is an sg3525an not sure what brand / but the STM and motorolla sheets I looked at were very similar



Supposed to have 8-40 VDC powering it, so looks like we drop out of range once the set is on.

If im interpreting the power supply schematic right they get 12v power(or whatever voltage vcc should be) from the smaller transformer? But I cant figure out how 12v(or whatever) comes out from the same side as the 400v goes in... does the transformer convert 400v on the primary to 24v on the secondary side , then convert that 24v on the secondary to 12v on the primary, or is it better to think of it more as 400v going through the transformer once, and you can layer as many outputs as you want off that, and have those output voltages leave on either side / wherever you have room to stick pins?

[budm]

Re: element eldft551 not turning on

"I think weve isolated the problem down a lot > the vcc2 reads 11.5 - 12 ish VAC against cause ground when the set is just plugged in , but when you turn the set on (LED lit blue) then it drops down to 9 VAC." You are working in the primary side, case ground cannot be used for ground ref point, the negative leg of the main DC filter cap in the primary side is the ground ref point of the primary circuits you are working on. The only time ou use the chassis as the ground ref point is when you are working on the secondary side (cold side).
The meter should be set to DC for checking the VCC2 DC Voltage.

[cashkennedy]

Re: element eldft551 not turning on

I retook the measurements using the negative leg of the main cap

vcc when off > 0
vcc when "on" > 15.1 V (I tested that in a few places along the path to the IC, as well as directly on the actual vcc pin of the IC

[budm]

Re: element eldft551 not turning on

That VCC2 is 15.1VDC? or that is VCC1?

[cashkennedy]

Re: element eldft551 not turning on

That's VCC2 as far as the "schematic" labels it. But the datasheet on the part shows pin 13 being VCC and pin 15 being VCC2, but both are connected so are essentially the same thing.

Sorry for the confusion.

[budm]

Re: element eldft551 not turning on

OK, so the IC is getting correct DC for it to function, I will have to look at the digram to see what else to check in that circuit.
So far that IC UA4 drive the coupling transformer directly, so it can be bad IC. Can you read the number on that IC?

[cashkennedy]

Re: element eldft551 not turning on

UA4 (the same IC I was testing VCC2 for) is the sg3525an that I linked a datasheet for above.

I did some testing based on the diagram and T4-A has 5vDC on pins 3 and 4 for 1-2 seconds after turning "on" then goes away. Also the FET's QA2 and QA3 read out of range (over 1000 vDC) for 1-2 seconds after turning "on" then goes away. So it appears the problem occurs at UA4 or somewhere upstream of that.