lg 60pz550 black screen, no power, etc

[budwich]

Re: lg 60pz550 black screen, no power, etc

:-).... you certainly need to be "good" with your testing / eyes since "our internet end" can't see anything else. Since the "new values" are more expected, you should probably go thru the latest suggestion by unspun01 and go from there.

[legonch]

Re: lg 60pz550 black screen, no power, etc

Okay. power board installed. no flat cables attached anywhere. Do not get the red light in front of the tv, remote doesnt work

Plugging in the tv while reading the 5v pin shows an initial voltage of 3.7, then drops to Zero

Reading the Va pin, i get voltage numbers all over the place. 137volts to 0. Meter voltage is constantly moving. Same readings while plugged in, and while powering up.

The bottom Vs pins register 0 volts.

This is my response to unspuns suggestions. Wondering if power board has a big issue with the lack of voltage, etc.

[budwich]

Re: lg 60pz550 black screen, no power, etc

BUT... you didn't read his "request" carefully... he did NOT request that ALL ribbon cables to the power board are disconnected.

[Unspun01]

Re: lg 60pz550 black screen, no power, etc

hmmmm.... I would expect any kind of resistor in / around any FET's or "switch transistors" to be in the 5-20 ohm range....

Good observation budwich - I skipped over the decimal.

Most of those resistors that I highlighted in red are 15 ohm or parallel 27 ohm resistors which would read 13-15 ohm. If someone measures in "resistance" mode they should appear as 13-15 ohm. If someone measures in "diode/continuity" mode the display may show 0.015 which corresponds to 15 ohm...

Legonch: can you please re-measure all the gate resistors I highlighted on ysus and zsus boards? They should be about 10-15 ohm or close to it.

[legonch]

Re: lg 60pz550 black screen, no power, etc

will do!!!

[legonch]

Re: lg 60pz550 black screen, no power, etc

Im attaching a pic of the zsus board.

All of the resistors on the zsus tested around 15 ohms. The one tested 48 ohms.

How do I test these little chips you have highlighted?

The ysus board, all the resistors checked at around 15 ohms.

What do I test next?

Thank you again for your help!!

[budwich]

Re: lg 60pz550 black screen, no power, etc

BUT... I think you need to EXACTLY do the test that unspun01 specify with the cabling as suggested... if in fact to ensure that there is no question as to what is connected and what isn't, post a picture of the "test setup".

[budwich]

Re: lg 60pz550 black screen, no power, etc

Im attaching a pic of the zsus board.

All of the resistors on the zsus tested around 15 ohms. The one tested 48 ohms.

How do I test these little chips you have highlighted?

The ysus board, all the resistors checked at around 15 ohms.

What do I test next?

Thank you again for your help!!

if that resistor is labeled / looks the same, then that it is a problem.

[legonch]

Re: lg 60pz550 black screen, no power, etc

yeah, that resistor is pulling that many ohms. Probably a stupid question, but can one single resistor cause the picture to not show at all? Seems like a tiny part for all that

[legonch]

Re: lg 60pz550 black screen, no power, etc

Okay. power board installed. no flat cables attached anywhere. Do not get the red light in front of the tv, remote doesnt work

Plugging in the tv while reading the 5v pin shows an initial voltage of 3.7, then drops to Zero

Reading the Va pin, i get voltage numbers all over the place. 137 volts to 0. Meter voltage is constantly moving. Same readings while plugged in, and while powering up.

The bottom Vs pins register 0 volts.

Okay, attached is a pic of how everything is installed. Everything hooked up except the ysus and zsus boards. I still get the same voltage readings as before.

Where to now? Power board dead?

[legonch]

Re: lg 60pz550 black screen, no power, etc

bump

[Unspun01]

Re: lg 60pz550 black screen, no power, etc

Wow, there are a whole bunch of replies to this thread that did not show up previously so my apologies if some of my replies are not timely or out of order.

Legonch:

Originally, you had a semi-working TV that stopped working after you re-soldered coil connections on the YSUS and ZSUS boards.

We started testing the YSUS and ZSUS boards because there was no reason to suspect the power supply until now.

You must have damaged something by accident so we must find out what.

Based on the YSUS and ZSUS tests I asked you for, I think those boards look ok for now.

HOWEVER, please post CLEAR pictures of the actual soldering you did on the backside of ZSUS and YSUS boards.

----------------------------

The photo requested by budwich is exactly what he and I want to see. All of the cables and boards are installed and connected except for the PWR-to-ZSUS and PWR-to-YSUS which is good.

******With this arrangement, please measure 5V, VA and VS with reference to TV chassis (ground) that I described in post #33.

Press power button and measure each voltage for 5-10 seconds. Let us know if you 1) measure a voltage?, 2) what is the voltage?, 3) whether that voltage stays on?, 4) if the voltage goes away?.

[legonch]

Re: lg 60pz550 black screen, no power, etc

Wow, there are a whole bunch of replies to this thread that did not show up previously so my apologies if some of my replies are not timely or out of order.

Legonch:

Originally, you had a semi-working TV that stopped working after you re-soldered coil connections on the YSUS and ZSUS boards.

We started testing the YSUS and ZSUS boards because there was no reason to suspect the power supply until now.

You must have damaged something by accident so we must find out what.

Based on the YSUS and ZSUS tests I asked you for, I think those boards look ok for now.

HOWEVER, please post CLEAR pictures of the actual soldering you did on the backside of ZSUS and YSUS boards.

----------------------------

The photo requested by budwich is exactly what he and I want to see. All of the cables and boards are installed and connected except for the PWR-to-ZSUS and PWR-to-YSUS which is good.

******With this arrangement, please measure 5V, VA and VS with reference to TV chassis (ground) that I described in post #33.

Press power button and measure each voltage for 5-10 seconds. Let us know if you 1) measure a voltage?, 2) what is the voltage?, 3) whether that voltage stays on?, 4) if the voltage goes away?.

I did post a pic of how the boards are connected now on the back of the tv. the ysus and zsus boards do not have the power board connections connected.

I did measure the voltage, the 5V i get an inital rise to 3.8 volts, then goes to zero. Va i get voltage all over the place, as high as 138, and low of zero. This cycle repeats constantly and never changes with the tv on. The VS pins register zero. I measured these voltages on both of the connectors to the sus boards on the power board.

[Unspun01]

Re: lg 60pz550 black screen, no power, etc

Please read my reply.

I am asking for clear photos of the ACTUAL soldering you did on the rear of the YSYS AND ZSUS boards.

You had a working power supply, but something you did to the YSUS or ZSUS may have burned out the power supply.

The VA and VS pins on the power supply should rise to the voltages stated on the label on the back of the panel. These voltages should remain constant.

The fact that you have no VS voltage tells me that you now have a power supply problem.

Since you did not touch the power supply, you may have damaged it by accident with something you did on YSUS or ZSUS boards.

[legonch]

Re: lg 60pz550 black screen, no power, etc

Here are the pics of my soldering on the sus boards.

The last pic, the board looks discolored for lack of better terms on the back side, is that the way it is supposed to look?

Thanks!!!

[Unspun01]

Re: lg 60pz550 black screen, no power, etc

legonch:

Thanks for your pictures of your soldering. They are very helpful.

The slight discoloration of the board is normal and may be from operating in a war/hot area of the TV, or may be present from manufacturing. Not an issue here.

Now for bad news.

Your soldering is not good. The coil soldering was not cleaned properly, and it looks like you did not use flux or enough solder.

These coils expand and contract a lot throuch heating and cooling, and therefore the solder connections break over time due to the brittle ROHS lead-free solder used at the factory.

What you need to do is remove the bad dark oxidized solder from the coils and the solder pads on the circuit board.

Then you have to use LOTS OF FLUX and a good soldering iron to "re-tin" the coils and the solder pads. You need to use a good amount of solder and ensure that you have good solder flow between the board and the coil legs.

What you have now is poor solder connections, and possibly no solder connections at all in a few of them.

The clean/new solder appears to remain clumped to itself and no adherence to the coil, or the board in some places.

To clean the crusty bad solder use de-soldering braid or de-soldering wick, and possibly gentle scuffing with an X-Acto blade to scrape off bad solder. When you have nice silver surfaces then you can re-apply solder.

Unfortunately, it looks like not one of the coil solder connections is good, and I suggest re-soldering every one of them.

Also, please re-solder the HEATSINK solder tabs and maybe the transistor legs because from the cracked pad with a black circle around it in your first picture, you also have poor solder connections at other locations on the board.

[legonch]

Re: lg 60pz550 black screen, no power, etc

okay, thanks!! i didnt remove the old solder, i just heated the pins up and melted new solder on it.

Would these have anything to do with the power board voltages not being correct? I do get continuity through all of these new soldered joints if that means anything.....

[legonch]

Re: lg 60pz550 black screen, no power, etc

Also, please re-solder the HEATSINK solder tabs and maybe the transistor legs because from the cracked pad with a black circle around it in your first picture, you also have poor solder connections at other locations on the board.


I didnt even see that until you mentioned that!!! Nice Catch!

[Unspun01]

Re: lg 60pz550 black screen, no power, etc

You still have a power supply issue, and it could be related to improper ZSUS or YSUS repair but I don't see any locations where your soldering created a short circuit - only incomplete repairs due to the soldering.

You definitely want to fix these YSUS and ZSUS issues because they will only cause you problems.

Regarding the power supply, please check fuses for continuity and test all diodes and transistors for shorts. There is an issue here that is causing your no voltage issue.

[legonch]

Re: lg 60pz550 black screen, no power, etc

Update.

I ordered a new power board. I couldnt find anything off following your instructions.

New power board installed. All cables hooked up except the ysus and zsus boards.

Redid all the solder I initially did. Totally clean nice solder job now.

I still have the same condition. The voltages measured at the 5v, Va, and Vs are exactly the same as when the other power board was installed. Also the voltages on the fuses remain the same. Lower fuse on power board reads 120, the other two read 62-62 volts.

Where do we go to now?