lg 60pz550 black screen, no power, etc

[legonch]

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

Okay, so I tested the zsus thoroughly. The fuse ohms out. however the fuse to the board doesnt. multiple locations on the board to not ohm out. Most if not all mosfets are grounded. Multiple capacitors are grounded. Im seeing basically half of the board with not register any ohms at all.

Am I correct in thinking this board is totally gone?

[legonch]

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

Well, more news. Yesterday I had the proper volts on both sus connectors. Today I do not.

The lowest fuse reads 120.8 volts. The other two fuses on the power board read 63

What does this mean?

The voltage at the sus connectors reads initially, but zeros out in a second. Exact same thing at both connectors Like there is a voltage, and then it bleeds away.

Power board suspect here?

[Unspun01]

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

Okay, so I tested the zsus thoroughly. The fuse ohms out. however the fuse to the board doesnt. multiple locations on the board to not ohm out. Most if not all mosfets are grounded. Multiple capacitors are grounded. Im seeing basically half of the board with not register any ohms at all.

Am I correct in thinking this board is totally gone?

"The fuse ohms out"??? This slang means exactly nothing. It means even less to anyone who does not speak English well. Don't use this phrase - remove it from your vocabulary actually. Nobody should ever use this junk ambiguous phrase. Use the word "continuity". The fuse has continuity or the fuse does not have continuity is immediately clear to anyone reading this.

I told you to check the 4633 IGBTs and their 7371 drivers on the bottom of the board. If one of these is shorted out, then you could measure a short to ground at multiple locations. You should try removing one "shorted" IGBT transistor at a time until therecently are no more left. Many of your other "shorts" may disappear with removal of the bad components. I don't recall but there may be about 6 of them.

This is usually a very repairable board. If you remove/isolate the bad components you have high chance of repair. But listen to advice on here and do not rush.

[legonch]

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

Dumb question, with the boards installed on the tv, cables unplugged, should you get continuity on every solder point if everything is in working order? Im testing the z and y sus boards, and the power board, and finding about half of the board there is no continutity.

About half of the 7371s have continuity on two pins, but not on the single pin by its self. The other 7371s have no continuity at all, this is on the zsus board.

[Unspun01]

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

legonch:

How are you measuring things? It sounds like you are trying to measure continuity from all components to the grounded TV chassis.

If you are measuring for short circuits from TV chassis to ZSUS and YSUS boards, there are MANY common ground points. If you do not know which ones are intentionally grounded, you will not be able to troubleshoot this board.

Please work on ONE BOARD AT A TIME, then proceed to the next board.

I don't think your problem is power board so leave it out for now.

Start with YSUS or ZSUS. Make it clear to us which board you are working on and do not lump together your observations for both boards since we do not know what you are doing.

Measure each of the 3-pin 4633 IGBTs. I've asked you to do this a few times and you still have not done this. I'm still waiting for your results.

There should be NO short circuits between pins 1-2, 2-3 or 1-3 for any of the IGBTs.

Some 3-pin diodes will have pins 1 and 3 tied together on-board but pin 2 should not measure as a short to pins 1 or 3. Diodes may measure a short in-circuit but may not be the issue if they are connected to a shorted IGBT.

You still have not said if the fuses are good? Are the fuses good or not?

[legonch]

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

ok, thanks. this is the zsus board. I took it off the tv, bench tested it. nothing attached to it.

There are three rows of these of these igbts. looking from the front, far left row, installed on a silver piece, no continuity on any of the four diodes.

Middle row of these under a long black piece, i get continuity on pins 1 and 3 for the top 7, the bottom three, i get no continuity

the last row, installed on a silver piece, no continuity to any of the six installed

I have continuity through the fuse, reading .3 ohms.

will wait for a reply before testing ysus board. Thank you for your help

[Unspun01]

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

I attached a markup photo of the bottom of the ZSUS board. I highlighted in RED each IGBT transistor and their gate resistors, and their gate drivers.

The red highlighting in my photo is:

Upper right area (the 4 parts are attached to small silver heatsink)

Lower left area (the 4 parts are attached to larger silver heatsink)

Lower middle area (the 3 parts are attached to large black heatsink)

I did not highlight the diodes on the heatsinks.



From your observations:

1) The 4 diodes look ok.

2a) The top 7 parts you measured are diodes. Pins 1-3 are physically connected together for each of them. If you have no short between pin 2 and 1-3 they are ok.

2b) The lower 3 IGBTs look ok if you do not measure short-circuit from 1-2, 2-3, 1-3.

3) The 3 IGBTs look ok if no continuity on all 3.

4) The fuse looks ok.


I think your ZSUS may be ok. Can you test between pins 2-3 on the white topside connector P102?

If you do not measure short-circuit here, then let's move on to the YSUS.

[legonch]

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

okay, ill attach a pic of my tests, hope you can see it. I do not register continuity between pins 2 and 3 on the p102

[legonch]

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

Here are my tests on the ysus board.

[legonch]

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

bump

[Unspun01]

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

Please see attached photos for YSUS checks to complete.

Unfortunately, your tests are not clear to me since I do not know what or how your are measuring.

On top side, measure the 3 fuses FS101, FS102, FS103 for continuity. You already said FS102 is good I think?

Also, check for short/continuity between GND and ANY of +5V, +VA, +VS on connector P113.

RED:
On the bottom side, please check for short/continuity in all of the 3-PIN devices highlighted. If you measure a short in any combination 1-2, 2-3, 1-3 then the component may be bad.

The gate resistors highlighted should be low resistance values. If they are high resistance, or "open", then they are likely bad.

YELLOW:
The devices in yellow are diodes and rarely fail, but can measure shorted if an associated IGBT is shorted. If you measure a short on any of these, double-check the RED highlighted devices.

PINK:
These coils can develop bad solder connections. If they look dark, or burned, or loose, then re-solder with lots of non-acid flux and leaded solder.

[legonch]

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

On top side, measure the 3 fuses FS101, FS102, FS103 for continuity. You already said FS102 is good I think?

continuity between all of these three fuses


Also, check for short/continuity between GND and ANY of +5V, +VA, +VS on connector P113.

No continuity between any of these pins



All the red highlighted items, there is no shorts detected. The resistors all have continuity, .15 ohms


Pink highlighted items show continuity.

[Unspun01]

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

Well, it looks like you didn't measure shorts on the ZSUS, or YSUS boards.

Let's go back to power board.

1) TV unplugged.

2) Connect everything except power wires (from power board to YSUS and from power board to ZSUS)

3) Place black multimeter lead on TV metal chassis and leave it connectd.

4) Plug TV in and turn on.

5) Measure voltage with red probe at 5V on power supply.

6) Measure voltage with red probe at VA on power supply.

7) Measure voltage with red probe at VS on power supply.

You may have to turn TV off and back on again to complete the measurements. We want to measure the voltages AS YOU TURN THE TV ON... We want to see if the voltages come up, and if they come up, what are they? and if any voltages do not come up.

Write back here.

[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.

[budwich]

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

there is something "strange" about "All the red highlighted items, there is no shorts detected. The resistors all have continuity, .15 ohms".... is the ".15 ohms" a typo or that the measurement? Have you looked closely at those resistor to see if there is any label on them to indicate value.... the value you list is basically a "short"... or at best, the resistance of the test wires.

[legonch]

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

the .15 ohms isnt a typo. Thats what all of them read. All the same, pretty much exactly

[budwich]

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.... and I personally have never seen a resistor below 1 ohm. Further, most meters unless they are "really good", would measure the reistance of the test leads in fractions of an ohm.... meaning that you potentially ARE seeing a short / near short.

[legonch]

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

Ill retest and publish the results.

Im leaning twoards the power supply board having an issue. I dont get any voltages at the connectors to either sus board

[budwich]

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

some time shut down happens pretty fast... depending on conditions and how you are monitoring things.

[legonch]

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.... and I personally have never seen a resistor below 1 ohm. Further, most meters unless they are "really good", would measure the reistance of the test leads in fractions of an ohm.... meaning that you potentially ARE seeing a short / near short.

Okay, did new testing. I got readings from 13.8 to 15.3 ohms. I apologize for the misprint above.

Anything else I should test?