Philips 42PF7320A/37 42" Plasma Repair

[stevekasian]

Hi all,

I have a Philips model 42PF7320A/37 42" plasma flatscreen that I got for free from a friend. It's in pristine cosmetic shape and is about 5 years old.

The problem is that there is no picture. Everything else worked before I brought it home, with no flashing light codes visible. Once i got it home, I plugged it in and turned it on and I get 2 relay clicks when I turn it on. There is a relay click when I turn it off as well, but I don't remember hearing any relay clicks at his house before I took it home with me.

My first question though, before going any further with this, is: How does one go about working on a plasma TV if you are supposed to keep it in a vertical position?

Thanks!

SK

[PlainBill]

Originally Posted by stevekasian

Hi all,

I have a Philips model 42PF7320A/37 42" plasma flatscreen that I got for free from a friend. It's in pristine cosmetic shape and is about 5 years old.

The problem is that there is no picture. Everything else worked before I brought it home, with no flashing light codes visible. Once i got it home, I plugged it in and turned it on and I get 2 relay clicks when I turn it on. There is a relay click when I turn it off as well, but I don't remember hearing any relay clicks at his house before I took it home with me.

My first question though, before going any further with this, is: How does one go about working on a plasma TV if you are supposed to keep it in a vertical position?

Thanks!

SK

You download the service manual from Elektrotanya. That will tell you that you can use Philips P/N 3122 785 90690 or Philips P/N 3122 785 90580 to service it. Also, it will show you that it is perfectly acceptable to lay it on it's face PROVIDED the weight is supported by the front frame, not the plasma panel itself.

Two other things -this TV is notorious for two failing 3300µF, 10V caps on the power supply. USUALLY with that failure it will flash an error code. It also uses the infamous LJ92-01200A - LJ92-01202A LJ92-01203A Y-sustain and Y-buffers. If those are the problem, IMHO, it's not worth repairing.

PlainBill

[stevekasian]

Thanks PlainBill.

I found and looked at it over at scribd.com before posting, but I couldn't find anything in it related to how to position it for service. I guess I didn't look close enough. Thanks for the info!

SK

[PlainBill]

Originally Posted by stevekasian

Thanks PlainBill.

I found and looked at it over at scribd.com before posting, but I couldn't find anything in it related to how to position it for service. I guess I didn't look close enough. Thanks for the info!

SK

Page 10 in the service manual.

PlainBill

[stevekasian]

;-)

[stevekasian]

Ok, got the thing taken apart and have all LEDs coming on with no flashers, except one on the logic board. It is buried beneath the IO board and, oddly enough, is not shown in the service manual. It has 2 LEDs on it - LED2010 and LED2011. LED2010 comes on when both relays switch on the power supply and their associated LEDs come on. Then, about 7 seconds later, LED2011 starts flashing at about 1hz. I've googled "LED2010 LED2011" (without quotes) and come up with lots of results, but none of them give any clue as to whether this is to be considered normal activity for these LEDs. Plenty of people asking about it flashing but no answers. Others mentioning different behavior with these as well, so it's hard to tell who's experiencing "normal" behavior out of all the references found.

I've checked continuity on all the major fuses on all boards and found them to be good, but have not disassembled anything yet to check any surface mount or radial leaded fuses. I don't see any caps that appear bad (although I realize this doesn't mean they are all good).

At this point, I'm kind of stuck on this LED2011 flashing deal. Would love to know if this is telling me something, but i find absolutely zero occurrence of the string "LED2011" anywhere in the service manual.

Any suggestions on that to do next?

Thanks,
SK

[PlainBill]

You have the 42" HD V4 Samsung panel. I don't see it in the pictures, but in the upper right corner (viewed from the back of the TV) of the plasma panel there should be a white label indicating several voltages.

The service manual for the panel is available at Elektrotanya. It is the next to last one in the list, and includes PHILIPS SDI PDP 14992 S37SD-YD02 in the title.

Check the voltages going to the Y-Sustain (left side in the picture).

The Coppell TV repair blog has several entries covering this panel.

PlainBill

[stevekasian]

I'll get the info from the voltage label shortly.; It is buried underneath chassis parts. In the mean time...

Unfortunately, there is no mention of the 2 LEDs on the Logic Main in the panel service manual either. Frustrating.

The Y-Sustain is called Y-Main in this manual (I believe - it matches the functional description of a Y-Sus board and is located in the same place).

I found 1, possibly 2, bad caps on Y-Main.

Also, Coppel TV Repair Blog is not showing any entries with either the TV model or the display model in the search results. Would U be so kind as to link to the entries you're finding there?

Thanks,
SK

p.s Including an image of Y-Main from the manual with annotation showing the location of the puffy cap(s), just FYI. I didn't take a pic cuz there is way 2 much chassis in the way right now.

[PlainBill]

Doggone it, do I have to do EVERYTHING by myself??

The blog entries are under the part numbers for the Y-Sustain and the Y-buffers.

http://blog.coppelltvrepair.com/2010_03_01_archive.html

http://blog.coppelltvrepair.com/2010_06_01_archive.html

PlainBill

[stevekasian]

Thanks for the links.

Here is the voltage label. Had to splice a couple images together because it wasn't 100% visible from any one vantage point.

[PlainBill]

Originally Posted by stevekasian

Thanks for the links.

Here is the voltage label. Had to splice a couple images together because it wasn't 100% visible from any one vantage point.

Check the voltages on the top line with everything hooked together, then disconnect the power cable to the Y-Sustain (with power off) and recheck. If the voltages are OK with the Y-sustain disconnected, you will have to replace or repair the Y-sustain and both buffers.

PlainBill

[stevekasian]

Sorry, but I have a dumb question: What do you mean by "the top line"?

Also, I've been reading about Y-Sus failures being primarilly due to bad design causing overheating, breaking down components over long periods with high temperatures. That sounds to me like bad caps could the primary culprit there. If so, do you think it would be prudent to re-cap the Y-Sus in an attempt to repair it, or do other components commonly go out on them as well? Thanks.

SK

[stevekasian]

I have checked all the voltages coming off the PSU on the main rails.
Unfortunately I could only check them with the Y-Sus/X-Sus & Buffer disconnected.

On the Y-Sus rail, all match perfectly with the PSU specs in the manual.

On the Buffer rail, all match perfectly as well.

On the X-Sus, all match perfectly except Ve, which reads 83.6v and should read 90v.

Ve is variable (80v ~ 105v) - Would it be advisable to adjust the Ve pot to the proper voltage before going any further?

[PlainBill]

Originally Posted by stevekasian

I have checked all the voltages coming off the PSU on the main rails.
Unfortunately I could only check them with the Y-Sus/X-Sus & Buffer disconnected.

On the Y-Sus rail, all match perfectly with the PSU specs in the manual.

On the Buffer rail, all match perfectly as well.

On the X-Sus, all match perfectly except Ve, which reads 83.6v and should read 90v.

Ve is variable (80v ~ 105v) - Would it be advisable to adjust the Ve pot to the proper voltage before going any further?

There are two possible causes for the original problem - a defective power supply, and an excessive load caused by a defective sustain board (or buffer).

Will the power supply stay on if ANY one of the various loads (Y-sustain, buffer, X-sustain) are attached? If the answer is no, the problem is most likely the power supply. The general idea is simultaneous failures of all three loads are unlikely.

PlainBill

[stevekasian]

The PSU seems to operate normally with no error codes and no difference in activity whether any of the buffers or sustain boards are connected to it or not.

I am wondering if 1 or more bad caps could be responsible for the low voltage on "Ve". I don't think that is related to the main display failure issue, but if I do fix said issue I might have another (low voltage) problem to deal with. Hmmm.

[PlainBill]

OK, I see I missed a couple of points.

I was thinking the TV turned off my itself; I see it stays on. I also missed the fact that you were testing voltages with the cables disconnected.

You will either have to rig an adapter or find a narrow probe, but the voltages are pretty meaningless without the proper load. I have found a DMM probe will slide into the top of the connectors next to the wire and make contact with the terminal.

Yes, the low Ve is an item of concern, as are the bulging caps on the Y-main.

Before you get too tied up in that, there is one simple test you can perform. Hook up a signal source (DVD player, video game, etc) that is producing sound and see if you hear audio as you cycle through the inputs.

One other thing you can try is searching on elektrotanya for samsung plasma training manual. After going through several manuals I have only a vague idea of how the Y-sustain does it's thing, and the correlation to the Z-sustain.

[stevekasian]

As stated in my original post, everything seems to work except the screen.

As for the low voltage, I was referencing the manual for the voltage specs instead of the sticker (which I just posted a picture of earlier). According to the sticker, Ve is supposed to be at 84v, so all is good (without a load). I will attempt to get my probes into the pins while the boards are connected and see if I can't get some readings under load without blowing myself up ;-).

Training manual: http://elektrotanya.com/samsung_2009.../download.html

Exerpt:

Y Board Circuit Explanation

This Y Main board maintains the sustain voltage waveform, the initialize waveform and generates the Y rising/falling ramp waveforms. The wave shape that is output to the respective Y electrodes varies depending on luminance levels and whether that pixel is actually selected. Y board failures usually cause the entire panel to be dark. Y board failures can sometimes be verified by visual inspection of the IC and FETs.The Y board operates similarly to the X board with some variations. The Y board output signal is opposite in polarity to the X Board signal. The Y Board signal is specific for each pixel. Pixels that are off do not receive a signal. Pixel brightness is controlled by varying the number of sustain pulses. Because the Y board signal is more detailed than the X board signal is output to a pair of multiplexing boards. The upper and lower Y buffers divide the screen in half vertically. The Y Buffer Boards
apply the address waveform to the Y terminals of the panel. The Y Board signal varies depending on the input video. Each Y electrode gets a unique signal; this means that the Y signal is applied through an upper and lower buffer board.

X Board Circuit Explanation

The X board contains a series of FET drive transistors. The Vs and Ve supplies are connected to these FETs. The Vs supply is approximately 200V and the Ve supply is approximately 100v. The Logic PCB triggers the FETs creating the X Drive waveform. The X Drive waveform is the same regardless of the video input signal. Variations in the Ve voltage may not be immediately noticeable on normal video but eventually the unit will display impurities. Apply a white pattern and look for red dots in the pattern, this indicates an error in the Ve supply Voltage. The X board generates the initialize and sustain signals to the X electrodes. If the X board is defective there will be no luminance and the pixels cannot be initialized. No luminance will be shown as an n extremely dark gray picture that may only be seen with the room lighting off. No initialization may cause the picture to show a reddish hue in spots with the redness filling the entire screen over time. X board failure can often be determined by visual inspection of the transistors on the heat sinks. The X board signal discharges the pixel before each new line of video and controls the sustain time of the pixels. Sustain time which equates to pixel brightness is controlled by the number of sustain pulses. The X board signal does not change and is applied to all pixels.

[stevekasian]

Checked voltages with everything hooked up. All voltages seemed to jump around in strange, time synched yet random intervals:

Contact .|. No Load . | . . Loaded
D5V________5.2v_____4.92v to 3.2v
D3V________3.3v______3.2v to 2.8v
Vg________15.14v____14.3v to 10v
Vscan____-190.8v____-190v to -189v
Vset______195.9v_____186v to 158v
Vs_________204v_____193v to 159v
Va________70.2v_____66.8v to 37v
Ve_________84v_______80v to 60v

[PlainBill]

Originally Posted by stevekasian

Checked voltages with everything hooked up. All voltages seemed to jump around in strange, time synched yet random intervals:

Contact .|. No Load . | . . Loaded
D5V________5.2v_____4.92v to 3.2v
D3V________3.3v______3.2v to 2.8v
Vg________15.14v____14.3v to 10v
Vscan____-190.8v____-190v to -189v
Vset______195.9v_____186v to 158v
Vs_________204v_____193v to 159v
Va________70.2v_____66.8v to 37v
Ve_________84v_______80v to 60v

When I encountered a TV with shorted buffers / sustain only one voltage (Vset?) was jumping around. The quickest and easiest approach (not that it's that quick or easy) may to pull the sustain boards and buffers and check them for shorts. It may be possible to check for shorts without actually pulling the boards. If it is necessary, do read the panel service manual first for the proper technique in removing the connectors from the plasma panel to the buffers.

PlainBill

[stevekasian]

-- disregard --