LG 50PJ350-UB Power board problem

[LDSisHere]

Re: LG 50PJ350-UB Power board problem

Optoisolator's rarely, but not never, go bad. I think I recall one bad one in almost 3 years of participation.

I had the experience of frying one of these a few weeks ago when I was working with the Viper22A board. Since I had fried some FETs and an IC on this board I just was not sure what else I could have damaged so I just want to be sure. I just look at it all as a learning experience about how circuits work and what I should expect to see when I probe something with my meter(s).

Your link to digikey says part not found so I don't know what you are looking at.

Apparently after you add something to an order list the link will not work for others, so I will keep this in mind in the future.

The Fluke 77 IV can read up to 60M ohm. Without knowing the part number, I can't be sure if RL101 is bad.
Obviously, you should desolder the component (relay) and measure it out of circuit to verify.

I pulled them both as you suggested and I quickly learned that I had jumped the gun on thinking one of them was bad. When I got to that point last night I was tired and it was late so the conclusions I drew were way off the mark. RL103's function is to bypass the two thermistors TH101 and TH102 when the supply comes out of standby. RL101's function is to pass the mains voltage that RL103 passed to it on to the main rectifier diode D101. When I pulled both relays and they both were open I realized the 15 ohms I was reading was the series resistance of TH101 and TH102

PS. Your pics are excellent. In addition, it helps a lot when you highlight the problem area so I don't have to spend my time searching for the component. I don't have selldoor's eyesight.

Thanks for the compliment, I have been trying to get better at taking pictures and I will try and highlight the areas I am describing in the future since it is helpful.



I now think the power supply is working properly. I was depending on the manual to tell me each step and I was not thinking the fluctuating standby voltage completely through. I have come to the conclusion that the voltages listed on page 42 are what you would see if you probed the pins while it was connected to the Main board. After many hours of tracing circuits, pulling and testing components it dawned on me that the reason the standby voltage was not stable was not because of a faulty component but due to a lack of load. As soon as I put a 100 ohm resistor from standby to ground the circuit stabilized at 3.434V. This is 0.2V less than listed but I do not think that is enough to be concerned about.

Since I can manually get the supply to turn on and off as described on page 41 and VA is 206.0V, VS is 60.1V and M5V is 5.1V I think it is working properly. AC Det is 4.961V compared to the 4.44 listed but this was taken with the connector disconnected and no load on the AC Det circuit which may explain why it is a little high.

I have not found a good way to probe the voltage levels between the power supply and Main board as of yet so I cannot say how far it goes to in the start-up process but no voltage is ever applied to VS. I had my meter set to hold the MAX voltage level and it never rose above ~1.5V even though I could hear the relays working. At this point I figure the best thing to do is read, research and figure out how and where to tap into RL On, AC Det, and M_ON while trying to turn the TV on so I can know how far it goes into the start-up cycle before it stops.

Thanks for taking the time to assist me in trying to figure this out, there is not doubt I have a lot to learn and need all the help I can get. Especially when I seem to cause a lot of my own problems. As I seem to like to fry components fairly regularly.

Thanks,
Lloyd

[LDSisHere]

Re: LG 50PJ350-UB Power board problem

You may want to check the two green thermistors right below the relays. They act as circuit protection and can shut down a power supply. I had one that was cause of failure before, and now that I think about it I'm pretty sure it was an LG. It looks like there's a black one also off to the right between the coil and red connector. (Actually I think one's a thyristor and the other is a thermistor?? I always confuse the two)

Anyways to check them you'll need to google the part number and see what the resistance should be out of circuit

Thanks Cosmo66 for pointing this out, it helped me understand what was going on a lot after I pulled the relays and was probing around this area. The resistance was good when I checked them but I did not know that for sure until I followed your advice.

[retiredcaps]

Re: LG 50PJ350-UB Power board problem

Thanks for taking the time to assist me in trying to figure this out, there is not doubt I have a lot to learn and need all the help I can get.

Sometimes it helps to have another perspective or bounce ideas off. I don't profess to have any expertise in plasmas, but a SMPS is a SMPS "more or less".

You will certainly learn a lot by working on the "tough" problems versus the "simple" cap replacement repairs.

Currently, I'm trying to repair a 30 year old Fluke multimeter. Yes, I have spent a lot of hours on it and the payback in terms of $$$ is certainly not worth it, but I'm learning new stuff and while it can be frustrating, I'm hoping to see it actually measure something once I'm done.

[LDSisHere]

Re: LG 50PJ350-UB Power board problem

When I was working on the power board I was not getting diode readings that matched what was in the training manual, even after I got it working. I was not sure what was going on so I did not test any of the other boards using this method until yesterday. It was only after I read the fluke manual where it said it only diode tested up to 2.4V that I realized why my readings did not match. Anything over 2.4V would show up as open not the value listed in the manual. Since then I have done some reading and probing, the results do not look good. I am certain the Y-SUS and Z-SUS boards have multiple failed MOSFET's after testing them out of circuit. These MOSFET's are proving very hard to source as the chip manufactures does not even list them on their sites. However, I can get both boards for around $50 from a reputable dealer thus saving myself a lot of hassle. The upper Y-Drive also failed the diode test, the results that did not match the listed ones and are marked on the attached image. Anything not marked was within a few hundredths of a volt or over 2.4V so not testable with my meter. Should I replace this board also?

I also have another concern and that is I am not even 100% sure the screen is good. It looked to me that someone may have "worked" on the Y-SUS board in the past. I am thinking they may have ran it disconnected without removing the Y-Drive boards like the manual warns you about and thus causing a lot of the problems. Since I got this off of Craig's list I have no idea what was done to it. I do not have a reason to think the screen is bad but I do not want to dump even more money into this thing if the screen could have been fried. Can shorted mosfets on the Y-SUS and Z-SUS take out the screen? Should I just get the SUS boards and see if the upper Y-Drive is bad or just spent an extra $25 and get the upper Y-Drive at the same time? Or do I quit now and sell the parts to get my money back out of it as best I can since it may become a money pit that will never work? I am not sure which way to go at this point.

You will certainly learn a lot by working on the "tough" problems versus the "simple" cap replacement repairs.

Very rarely do I ever get a simple fix. The stuff I get to work on usually have been been worked over by Murphy and his law to the max before I get it in my hands. I was hoping this TV was going to be a simple fix but it has gone from bad to worse.

Currently, I'm trying to repair a 30 year old Fluke multimeter. Yes, I have spent a lot of hours on it and the payback in terms of $$$ is certainly not worth it, but I'm learning new stuff and while it can be frustrating, I'm hoping to see it actually measure something once I'm done.

I think you have quite the challenge there. Is this meter analog or digital? (Has Fluke ever made and analog meter?) It sounds like it could be a pain in the rear especially trying to figure out what some of the parts are or suitable replacements due to the original ones age.

[tom66]

Re: LG 50PJ350-UB Power board problem

Shorted FETs cannot damage the screen. It is glass, noble gases, and electrodes.
You do have horizontal drivers which can fail but they cause lines, bars, etc. on the panel.

[LDSisHere]

Re: LG 50PJ350-UB Power board problem

Shorted FETs cannot damage the screen. It is glass, noble gases, and electrodes.
You do have horizontal drivers which can fail but they cause lines, bars, etc. on the panel.

Thank you for this information, it is good to know that the screen should be OK. The control board passes all the tests and I now believe that the main board is good. I think the reason I never saw any VS voltage when connected to the Y-SUS board was because of the shorted MOSFET's or at least I hope that is the reason. The VS voltage is on the dot when connected to the load tester.

[retiredcaps]

Re: LG 50PJ350-UB Power board problem

It was only after I read the fluke manual where it said it only diode tested up to 2.4V that I realized why my readings did not match. Anything over 2.4V would show up as open not the value listed in the manual.

1) Yes, the 17x and 77 IV test up to 2.4V on the diode range. The 80 series goes up to 3.0V on the diode range.

2) How are you interpreting the "run" column?

3) The only test on page 71 that would lead to some ambiguity is pins 21-23. It says the "correct" reading is 2.8V. If your 77 IV shows 0L and around 0.41V, I would say it is probably good.

[LDSisHere]

Re: LG 50PJ350-UB Power board problem

2) How are you interpreting the "run" column?

I have not been able to do the run tests on anything but the power board. The Y-SUS and Z-SUS have multiple shorted\damaged FETs.

3) The only test on page 71 that would lead to some ambiguity is pins 21-23. It says the "correct" reading is 2.8V. If your 77 IV shows 0L and around 0.41V, I would say it is probably good.

I used a poor choice of words to discribe my results. Two readings were completely different from what the book said they should be when tested.

YSUS_DATA (Red probe on FG) was supposed to be open but I had a reading of .637V

YT_DATA (Black probe on FG) was supposed to be open but I had a reading of 1.4V

My issue with the manual is that I have found several mistakes throughout it which makes me have doubts about completely trusting it. Look at page 110 for example. D1, D501, D504, and D505 pin "C" is being called pin "A". On page 69 it has:

FG5V TP
Open with Red Lead on Scan
0.41V with Black Lead on Scan

This should be:

FG5V TP
Open with Red Lead on FG
0.41V with Black Lead on FG

I think I have found more but I do not recall exactly what they are right now but I think you get my point.


I will hopefully know for sure tomorrow if my diagnosis pans out or not. This morning I ordered the Y-SUS, Z-SUS and upper Y-drive and I should get them tomorrow according to UPS. All three boards including shipping, and tax cost me $84.38. I intend to do some diode mode testing on these boards prior to installation for comparison purposes and reference. I am suspecting someone ran the Y-SUS board with the upper Y-drive disconnected but not removed and this resulted in the destruction of the Y-SUS and Z-SUS boards.

I would have tried to repair these boards if I could have sourced the FETs for a reasonable price but I got the entire boards for approximately the same price and I do not have to wait for them to get here from China. I also do not know if any of the other "chips" on these boards are damaged from the shorted FETS like I did when I shorted the power board FETs. If these boards do not fix it completely, they should at least allow me to better diagnose what else is wrong with it. (Unless if use a hammer to fix it permanently. ) Maybe I will at least learn to follow my own advice that I have given others, which is to stay from Plasma TV's.

[retiredcaps]

Re: LG 50PJ350-UB Power board problem

YSUS_DATA (Red probe on FG) was supposed to be open but I had a reading of .637V

YT_DATA (Black probe on FG) was supposed to be open but I had a reading of 1.4V

Unless the diode reading reads the same both ways or very low (like 0.023V), I usually don't tread the above readings as a short especially when they are done in circuit.

On the Fluke that I'm trying to fix, I measured a zener diode in circuit and it showed 0.023V both ways. I desoldered on leg to verify, found it was good, tried to re-insert it and the other leg broke off!

For finding shorts, I like to use resistance measurements or continuity. On the Fluke 77 IV, continuity is defined as less than 25 ohms. If it beeps, it is likely shorted. As you know, the Fluke continuity feature is very fast.

My issue with the manual is that I have found several mistakes

Either that or there are multiple revisions of the board and you may not have the same one?

I would have tried to repair these boards if I could have sourced the FETs for a reasonable price but I got the entire boards for approximately the same price and I do not have to wait for them to get here from China.

I probably would have done the same if the price are the same.

Maybe I will at least learn to follow my own advice that I have given others, which is to stay from Plasma TV's.

I prefer plasma over lcd for watching movies.

Lcd TVs also have their own problems as well: tab bonds failing, cracked ccfls, bad inverter transformers, bad t-con, etc

[tom66]

Re: LG 50PJ350-UB Power board problem

I find most plasmas easier than LCDs. Much less variety in a plasma display compared to an LCD for example.

[retiredcaps]

Re: LG 50PJ350-UB Power board problem

I find most plasmas easier than LCDs.

I'm the opposite since I started with repairing LCD computer computers I find it "easier" to understand LCD TVs.

[tom66]

Re: LG 50PJ350-UB Power board problem

I will say though, a scope is basically a requirement for debugging a plasma display, whereas an LCD can usually be debugged without one.

[LDSisHere]

Re: LG 50PJ350-UB Power board problem

I am very pleased to report that the boards I ordered work and the TV is now working. I did a diode check on the new boards before installation and I think I was correct in replacing the three boards I thought were bad. The original upper Y-drive had one test point that failed the diode test and the resistance was ~68 ohms both ways. The new one was open on the diode mode which was the way it was supposed to be and was in the megaohm range.

I do have another problem now and I am very afraid I am going to be told I need an oscilloscope to solve it. The picture does not line up properly. What I mean by this is that it looks like the red is shifted slightly to the right from the rest of the image on the screen. It may be all three colors are shifted from each other but I cannot be sure as it would take a stable image and all I had at that time was TV shows. If someone can please tell me how this can be adjusted I would appreciate it. If you can tell me how to do it without an oscilloscope it would be even better.

I want to say thanks for the help I have already received, I have learned a lot from this experiance. More than I wanted to learn actually.

[tom66]

Re: LG 50PJ350-UB Power board problem

Very odd. I have never seen that with a plasma display. Make sure the connectors on the control board and X-driver boards is correct.

[LDSisHere]

Re: LG 50PJ350-UB Power board problem

It turns out ghost images were due to the signal source, once I had a chance to actually check it out.

The power supply hums slightly when the set is on, but you can only hear it when you get next to it. Is this also normal or does this indicate there is still a problem?

As best as I can tell everything else works really good. My kids are excited as they can now see their games the way they were meant to be seen.

Thanks again for all the help guys!!!

[Bafury]

Re: LG 50PJ350-UB Power board problem

If there is no power at all, then it's the 6 pin chip 3BR1565JF that's the culprit. I've created a repair kit to fix the LG 50PJ models, but i've also noticed that the Infineon 3BR1565JF chip is also in the LG 50PJ models and some Zenith models.. Please troubleshoot your set first before making any purchases. After purchasing, email me and let me know if your power board has two or three white resistors located at the top right corner of the board

Repair kits NOW available on Ebay NOW! 50PJ models

http://cgi.ebay.com/ws/eBayISAPI.dll...m=191149541749

[cricoc]

Re: LG 50PJ350-UB Power board problem

Hi, ¿what it´s the specificatión of the diode d304 ? Best regards

[WBA]

Re: LG 50PJ350-UB Power board problem

For what it's worth , I had one of these (50PJ340-UC) in for repair, bought the repair kit, installed everything correctly, and all I got was the "click" twice just as before.

5v was present all the time.

After inspecting the P/S board with a magnifier very carefully, I found poor solder joints on the two big yellow xformers . (Very small rings around the joints) After re soldering,
Everything worked just fine !

[Wilderone]

Re: LG 50PJ350-UB Power board problem

Repaired 2 of these Power Supply boards recently with both suffering cold solder joints.