Electrohome 42E900 TV - No video

[Deviant69]

I just posted this over at the AVS Forum also, but perhaps you guys will have more information:

I just came into possession of a plasma TV that is not fully working and I'm trying to determine if it's worth the cost to fix it. (It was free, which is the only reason I'm considering it.) This model uses mostly Samsung components. The condition is as follows:

- No video, but the panel is clearly getting a slight hue when powered on.
- Sound is working, but volume control is not.
- Front panel buttons don't appear to be responding, except for the power button.
- The remote was not with the TV.

I'd like to narrow down which boards I should try to replace so I don't end up throwing too much money at it. All the voltages from the power supply seem to be present and correct, the diagnostic LED on the PS is solid-green, and all fuses are good. (One fuse had over 700 volts present at it - this seemed a little high.) The main logic board is an LJ92-01270A. Installing the test-mode jumper on this board does not generate the expected all-white image. LED #2010 is on solid, while #2011 is flashing - I don't know if the flashing is normal because I can't find these two indicators documented. If I buy a replacement LJ92-01270A do I need to be concerned with it having a specific firmware on it?

There is no visual evidence of bad capacitors anywhere, and I would have expected worse problems if there were any. I have to suspect the CEE062A Scaler board first-off because the unresponsive buttons are connected to it and it works hand-in-hand with the CME038A AV board to pass video to the LJ92-01270A. The LJ92-01270A may also be bad because it isn't generating the white-screen test. It would appear more than one board is bad because these problems should not be all related to one stage in the chain. The only evidence I have that any video might be making it to the X and Y panel boards is that feeding an external video source through the active input (side composite connector) changes the 'character' of the barely-audible buzzing from the power supply.

This TV appears to be essentially identical to a Sansui HDPDP4200 and also a Philips-Magnavox model. I have located a service manual for the Sansui and also for the Philips but neither of these provides any useful detail about the AV or Scaler boards. I would greatly appreciate any advice on isolating the culprit(s).

Major boards and part numbers:
LJ44-00101A - Power Supply (I couldn't find this number on the PCB but I found it in the service manual.)
LJ92-01199A - X-Main
LJ92-01200A - Y-Main
LJ92-01202A - Y-Buffer (Upper)
LJ92-01203A - Y-Buffer (Lower)
LJ92-01054A - Logic Buffer (E)
LJ92-01055A - Logic Buffer (F)
LJ92-01270A - Main Logic
CME038A - AV In/Out
CME062A - Scaler (and VGA input)

[Deviant69]

Re: Electrohome 42E900 TV - No video

After some additional investigation this evening, volume control is now working for no apparent reason. Perhaps it was something in the numerous cable connectors on the Scaler board because I had since detached and re-attached all of them while looking for the board part number.

I did the Y-Buffer disconnect test. The upper Y-Buffer appears to be bad because when the lower buffer runs alone there actually is something displayed on the bottom half of the screen - not anything much recognizable though. Black areas show scattered sparklies throughout. It was enough to prove that the on-screen display data is actually reaching the screen. The volume indicator shows up as huge vertical bars of white and orange - you can actually see the pattern of the volume bar moving in response to the controls though. The menu comes up as well but is just a solid white block. The input select button appears to be cycling inputs properly now.

Upon very close second inspection I've found one swollen capacitor on the Y-Main board. It is 50V 100μF. I've read that if one of the two Y-Buffers is bad then it is recommended to replace both upper and lower as well as the Y-Main. Is this really necessary, given the results of the test, or can I just replace the bad upper and the capacitor? Is the junk image the result of a defective main video logic board?

[martino]

Re: Electrohome 42E900 TV - No video

pictures of the fault would greatly help here. Also pics of the boards.

[Deviant69]

Re: Electrohome 42E900 TV - No video


(OSD of volume control with only lower Y-buffer connected.)

I've taken photos of all the major components and put them online in the following gallery:

http://s1262.photobucket.com/user/Sp...%20Plasma%20TV

Photos of the screen sparklies and vertical bars have been included, and there are part numbers, descriptions and notes on every photo.

What I gathered from a service person's advice somewhere else online is that repeated screen data vertically indicates a shorted Y-buffer. This would suggest the lower Y-buffer board is also bad, but the main video logic could still be defective anyway. I don't know what bearing this might have on the condition of the Y-Main.

I can't find the correct capacitor for the Y-Main (YSUS) on eBay. It is 50V 100μF 4x7mm. Can anyone suggest a suitable alternative source (without a minimum order charge)?

[Deviant69]

Re: Electrohome 42E900 TV - No video

One other question - What is the push-button on the main logic board used for? (It is near the left side. You can see it in the photo I posted of that board.) I'm not sure if I should try pressing it. The service manual only mentions the test-mode jumper, but nothing about the button.

Also, too late to edit my last post, but the capacitor noted above, 50V 100μF, should be 10x18mm size. Somehow I wrote down the wrong one.

[Deviant69]

Re: Electrohome 42E900 TV - No video

Well, I now know what a bad buffer IC looks like. I purchased a pair of Y-buffer boards from eBay which the seller said were "removed from a working environment". Contrary to that statement, one of the boards was horribly burned all around and under one of the individual buffer chips that had catastrophically failed. (While one of my original Y-buffer boards seems to be defective, it doesn't have any evidence of burning.)

Further to my bad luck I also purchased a supposedly working Main Logic board from another seller on eBay. This one causes the power supply to shut down after a few seconds. The power supply flashes the error LED 13 times which is listed on the PS board as a "Time Over" condition. Does anyone know what that implies?

So I still have a defective TV, and the parts I started with are 'less defective' than the replacements I ordered. I'm starting to wonder if I'm wasting my time and money. If anyone has more advice to give I'd certainly appreciate it.

[Deviant69]

Re: Electrohome 42E900 TV - No video

In today's news, I managed to get a full refund from eBay for the Y-buffer boards. (They didn't even require me to send them back!) I saw a YouTube video today of a guy showing a simple way of testing for shorted buffer lines. It's a basic continuity check with a multimeter between the output pins for the screen ribbon cables and the high-voltage input to the Y-buffer boards. Every pin on my original boards and on the lower board from eBay showed a consistent resistance. Compare this with the pins around the fried chip on the bad upper board from eBay - The burned tracings had no continuity, and a few others were almost fully shorted. Interestingly, every other pin on all the other chips on that board was fine.

This doesn't completely rule out defects in these chips on the original ones or the second set, but it is pushing my suspicions back towards the logic board. I noted while doing the continuity check that almost every pin on both input connectors on each Y-buffer board is directly linked together to one common high voltage plane. Even the smaller connector that bridges the two buffer boards to each other is just repetition of this one common voltage plane. This would suggest that the buffers should work even if that link is left disconnected.

I also received a remote control from eBay, and it works! I've added a photo of it to the gallery I linked above. Small progress but progress none-the-less. Now I'm waiting on a second replacement main logic board and another (non-fried) upper Y-buffer. I am a bit more confident in the sellers' proclamations this time about the functionality of these boards.

[ReeceyBurger123]

Re: Electrohome 42E900 TV - No video

Looks to me like a Ymain buffer ram Ic's (NOT THE Y BUFFER BOARDS EITHER THE BUFFER RAM CHIPS ON THE YMAIN) are at fault. The Ymain isnt loading the panel properly and is sending incorrect signals to the buffers. I have a Ps50Q97Hd with similar glitches the fault is with the Ymain. Btw your buffer boards are fine you should see some resistance. Have you an image of the Ymain ?

[Deviant69]

Re: Electrohome 42E900 TV - No video

Here is the image I have that was part of the gallery link I posted:

Samsung LJ92-01200A Y-Main (Y-sustain) (direct link)


(Upper Y-buffer board was removed at time of photo.)

I've pulled the board out of the TV just now in preparation for replacing the one swollen capacitor (the only obvious visible fault I could find in the entire TV). There actually seems to be very little physical logic in the path between the video input and output stages of this board. While it's entirely possible that a fault on this board could cause erroneous data to get sent to the screen, I'm not seeing much that could affect this in a way that almost purely repeats one line of image data over and over. Once I get that capacitor replaced I'll be more certain of what I'm dealing with. I'll post another photo of the board tomorrow now that it's been removed and will provide an unobstructed view.

The primary reason I'm suspicious of the main logic board is that applying the test-mode jumper doesn't yield the solid white screen expected, nor does it seem to have any effect at all. Video will get from the external connections via the input switcher to the screen but it is a garbled mess. You can tell there is motion going on but there is no valid image. If my original Y-buffers are actually good then I'll end up with a spare pair, which definitely isn't a bad move.

Keep in mind that the screen won't show anything at all if the original upper Y-buffer is present, which suggests multiple points of failure. This makes it harder to test properly. Thankfully the power supply seems to be operating perfectly to spec. Do you have any suggestions on how I can test further in order to isolate the problem?

[Deviant69]

Re: Electrohome 42E900 TV - Bad picture (was No video)

I've added the full image of the Y-Main removed from the TV:



The swollen electrolytic capacitor is the one in the upper right of the photo, nearest the big blue component.

One new experience now that I got a second new main logic board. (The last one caused a safety shutdown, as mentioned prior.) This one allows the TV to power on and stay on, but it actually won't shut off and doesn't seem to be responding to commands. The green light on it that would normally be flashing slowly on the original board is not coming on at all. It never gets so far as turning on the screen. I assume I'm now dealing with an issue of firmware. All three logic main boards I now have are the same part number and same revision. I suppose if I was really determined I could remove the flash chip from the original board and transfer it over to each of the others to test this theory. I can't think of any other way to accomplish this.

Does anyone know which chip on the logic main board is the flash ROM?