Philips 30PF9946D/37D Chassis LC4.6U AA

[PlainBill]

This is a 30" LCD obtained through Craigslist. The previous owner indicated it worked well for some time, then started shutting off after several hours. Gradually the 'on time' decreased until it would no longer come on. With TV, remote, and users manual in hand I headed home with my treasure.

Setting it up and turning it on I noticed the backlights flashed very briefly - much less than half a second. Suspecting a shorted driver in the inverter, I pulled the back and started tracing. The connectors on the inverter were conveniently labeled, and a quick check showed the BL_ON signal went low briefly, then went back high. Conclusion: Not the inverter or the CCFLs.

Early the next morning I tried again. This time the backlights stayed on, I was able to bring up the menus, etc. As expected, it had static on the analog channels, and hooking the DB15 connector up to a computer I was able to get a good display. After about 15 minutes the display blanked again. I have been unable to revive it, other than the brief flash.

With power hooked up and the mechanical push-push switch on the side pushed in I get a red LED if the TV is turned off from the remote. Pushing the Power button on the remote causes the LED to turn orange for a few seconds, then green. About 5 seconds after going green the backlights flash. The LED will stay green as long as a video signal is fed to the TV. If the video signal is removed, the LED will go orange after about 1 minute.

I've pulled the power supply boards and all of the caps have an ESR below 0.1 ohm with the exception of two 10uF 450 volt caps on the standby power supply board. They read about 3 ohms. Even the main 820 uF 250 volt caps ESR is below .05. There were no obvious sign bad solder joints, and all power supply outputs seem to be normal. I'm not sure because this TV was designed to use two different LCD panels requiring different voltages and some of the boards are used for both LCD and plasma sets.

Abnormailties

The service manual indicates that by pressing 062596 Menu the set will enter Service Default Mode (SDM). At that point the front LED should start blinking any error codes. The LED flickers indicating it is receiving the key presses, but no error codes are flashed.

The service manual also indicates SDM can be started by shorting a pair of contacts on "the TV board", but doesn't give much help locating the contacts.

Any suggestions?

PlainBill

[Wizard]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Um, not that hard for you to figure out which pins is for turning lamps on from mainboard at the power supply. Only 2 signal lines and rest is ground and 24V.

If lamp on stays on. and 24V stays on as well, then you have to pull the lamp inverter boards and check for any capacitor bloats or bad solder joints. Some panels uses what is "different" from rest of CCFL is called EEFL which is electodeless lamps that is excited externally through glass by external caps fitted to both ends of tubes at high frequency (way higher than usual). Easy to see that only 2 thick wires instead of multiple plugs and one or two BIG pancake transformers wound with thick litz wires. Completely different from CCFL design of most LCDs.

SAM or SDM menu is bit hard to get there. enter 6 digits and hit either status or menu. Takes few tries. Error code via LED is only for "fatal" problem if mainboard detected something wrong with mainboard or SMPS lost a voltage or something only because there is no "feed back" from lamp inverters themselves. And true for all LCDs.

Cheers, Wizard

[PlainBill]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Um, not that hard for you to figure out which pins is for turning lamps on from mainboard at the power supply. Only 2 signal lines and rest is ground and 24V.

If lamp on stays on. and 24V stays on as well, then you have to pull the lamp inverter boards and check for any capacitor bloats or bad solder joints. Some panels uses what is "different" from rest of CCFL is called EEFL which is electodeless lamps that is excited externally through glass by external caps fitted to both ends of tubes at high frequency (way higher than usual). Easy to see that only 2 thick wires instead of multiple plugs and one or two BIG pancake transformers wound with thick litz wires. Completely different from CCFL design of most LCDs.

SAM or SDM menu is bit hard to get there. enter 6 digits and hit either status or menu. Takes few tries. Error code via LED is only for "fatal" problem if mainboard detected something wrong with mainboard or SMPS lost a voltage or something only because there is no "feed back" from lamp inverters themselves. And true for all LCDs.

Cheers, Wizard

I didn't make myself clear. This does not seem to be a failure of the backlight system. The signal to turn the backlight on goes on for a fraction of a second, then off. That seems to be caused by the video processor, not the inverter.

I've double checked the power supply voltages, all are within 5% of the recommended value. At one point I thought I was on a hot trail - one point that was supposed to be 263 volts DC was only 164. Then I discovered it was the rectified line voltage for the standby power supply.

PlainBill

[Wizard]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

As a test, jam the lamp on high from a source of 3.3V somewhere else via a 100-470 ohms resistor (just in case to limit current). and see what happens?

Cheers, Wizard

[PlainBill]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

As a test, jam the lamp on high from a source of 3.3V somewhere else via a 100-470 ohms resistor (just in case to limit current). and see what happens?

Cheers, Wizard

OK, I'll give that a try.

PlainBill

[PlainBill]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

One of my favorite authors when I was young was Arthur Canon Doyle. His Sherlock Holmes stories emphasized the importance of knowledge and getting the facts to assist in deducing the trail of events. In particular, 'The Adventure of the Yellow Face' showed the folly of jumping to unwarranted conclusions based on flawed logic.

To paraphrase Holmes's words to Dr. Watson, "Wizard, if it should ever strike you that I am getting a little overconfident in my powers, or giving less pains to a case than it deserves, kindly whisper 'Philips inverter' in my ear, and I shall be infinitely obliged to you."

I have spent the past week pursuing false leads, testing good components, etc. while the answer was in my hands more than a week ago. I believed the inverter was being turned on, then off by the scalar IC. In fact, as you pointed out, the inverter controller was turning it self off. Five minutes of retesting would have saved me many hours of frustration.

PlainBill

[PlainBill]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

It's Alive!!! It's Alive!!! And showing 'White Christmas' right now.

One of the inverter output transformers had a slightly lower resistance. Using my Sencore YF33, that transformer showed only 4 rings; all others showed 6.

PlainBill

[Wizard]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Awesome, PlainBill!

How did you fix this one? Lamp inverter transformers do and will fail once in awhile, due to rather thin winding failing and shorting out. Not much have changed with flyback transformers dying in recently old days.

Cheers, Wizard

[PlainBill]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Awesome, PlainBill!

How did you fix this one? Lamp inverter transformers do and will fail once in awhile, due to rather thin winding failing and shorting out. Not much have changed with flyback transformers dying in recently old days.

Cheers, Wizard

"The more things change, the more they remain the same."

What really p***es me off is that two weeks ago I was racking my brains trying to figure out how to test the inverter. Various ideas came up, including coupling my high voltage probe to the scope so I could see the output waveform. Then when it worked for 20 minutes I became convinced the problem must be elsewhere - who ever heard of an intermittent inverter?

Still, all's well that ends well.

PlainBill

[Wizard]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Lay your probe's (more nearer the tip) against core, positioning to get strongest waveforms on scope. Sometimes I get hash, "thunk!" of waveforms when trying to oscillate but it's thunking like a cracked bell, hash than a waveform (arcing/dying), or weaker waveforms than other same transformer. This is possible to do that because lamp inverters are always supplied with one voltage source.

Cheers, Wizard

[RicB]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

I know this is an old thread but i was doing a search for posts related to my problem, your post came up plainbill because it is close to the problem i am having, (NEC PX42VP4A) screen will come on and power light will stay green unless signal is present then i hear a "click" (coil I think) and the screen goes off and will stay off even if signal is removed until i power cycle the TV. A visual scan of the 3 boards shows no burns, no burned components and no bad caps except maybe these (see pics)



15 years ago i was working ina tv/vcr repair shop and just starting to learn when the company went under I have exhausted my level of know how and wouldn't mind some direction I am just guessing it is the power supply because of the current draw to the screen once a signal is in place. Your problem seems more complicated than mine plainbill any idea where i should start looking?

THNX for any help

[PlainBill]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

I know this is an old thread but i was doing a search for posts related to my problem, your post came up plainbill because it is close to the problem i am having, (NEC PX42VP4A) screen will come on and power light will stay green unless signal is present then i hear a "click" (coil I think) and the screen goes off and will stay off even if signal is removed until i power cycle the TV. A visual scan of the 3 boards shows no burns, no burned components and no bad caps except maybe these (see pics)

15 years ago i was working ina tv/vcr repair shop and just starting to learn when the company went under I have exhausted my level of know how and wouldn't mind some direction I am just guessing it is the power supply because of the current draw to the screen once a signal is in place. Your problem seems more complicated than mine plainbill any idea where i should start looking?

THNX for any help

Well, it wouldn't cost too much to replace any suspect caps, so that would be the first step. If that doesn't fix it, I wouldn't hold out much hope unless you can find a service manual. And I question if it would be worth the effort. That's a pretty low resolution display.

PlainBill

[RicB]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Well, it wouldn't cost too much to replace any suspect caps, so that would be the first step. If that doesn't fix it, I wouldn't hold out much hope unless you can find a service manual. And I question if it would be worth the effort. That's a pretty low resolution display.

PlainBill

thnx bill, i dont plan on putting much effort/money into this tv but it does provide a nice platform to learn from I will start with the 2 400v caps as they were the only ones to misbehave during an in circuit ohms test . i am a little confused about the resolution, it says the native is 480 x 853 but the max is 1600 x 1200...in theory this means i can run 720P and use a HD signal...is my assumption correct? this is my firsty plasma/LCD type tv so i am still learning I plan to use it as a tv and a computer monitor once I get a newer LCD

thnx again for your help

[Peter Chiu]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Found bad connection over T103 (on inverter board), resolder and fix the problem。Thanks!

[foak56]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Plainbill,

Resurrecting an old thread but I am having the same issue as you on my Philips 30PF9946D/37 ? What was your final resolution ?

Did you replace the inverter board or the standby supply/audio board, or main power supply or the small signal/3D comb filter board, or T-con board ?

Any light you can shed would be greatly appreciated ?

You stated above

"I have spent the past week pursuing false leads, testing good components, etc. while the answer was in my hands more than a week ago. I believed the inverter was being turned on, then off by the scalar IC. In fact, as you pointed out, the inverter controller was turning it self off. Five minutes of retesting would have saved me many hours of frustration."

What board is that inverter controller on ??? Thanks....

[foak56]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Does anyone if if PlainBill is still around to answer my question ????

[selldoor]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Does anyone if if PlainBill is still around to answer my question ????

Unfortunately not.

However he also said this
Re: Philips 30PF9946D/37D Chassis LC4.6U AA
It's Alive!!! It's Alive!!! And showing 'White Christmas' right now.

One of the inverter output transformers had a slightly lower resistance. Using my Sencore YF33, that transformer showed only 4 rings; all others showed 6.

PlainBill

He replaced one of the transformers.

[foak56]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

If Plainbill is sick or passed away, I am sorry. He seemed like he was a good source of information here on this forum. I am sure there are plenty of others who are as well.

As a newbie here on this forum, I take a strong interest in troubleshooting & fixing things myself. My TV is a new area for me. I would rather replace boards then fix at the component level as I don't have the proper equipment ( isolation transformer, Fluke meter, scopes, soldering station,,etc...) I have just a middle of the road multimeter

Well anyway , the strangest thing happen...I stripped this TV all the way down...taking out every board.....removing every cable connector....even had the LCD panel out of TV....I did not remove the T-Con board thou......I did notice that the LVDS connector to the Small Signal Board ( SSB ) was not quite seated flush..it was up on one side just very so slightly ( odd..not sure how it got that way.... )

Anyway, proceeded to re-assemble, made sure every connector was fully seated, and the TV seems to have self corrected itself......works perfectly.....

So I could have & may still have an intermittent inverter transformer problem ...time will tell....

Just not sure what caused the problem to begin with....

[selldoor]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Please to hear you got it fixed - maybe if you had posted the problem it might have been caught earlier as depending on how you described the problem unplugging cleaning and reseating cables is likely to have been near the top of the list.
As to how - may never have been properly fitted heat over years may have caused it to loosen - What you should do is when you put it back in Tape it in position.
Well done!

[foak56]

Re: Philips 30PF9946D/37D Chassis LC4.6U AA

Selldoo

Thank you very much for your replies....much appreciated...

Maybe I just got lucky for awhile.....time will tell....



My initial post on this problem in another thread was:

Guys,

When I power up my TV, the picture & sound are fine. After about 1-2 minutes, the screen goes black, yet I have sound on all channels but a black screen on all channels....

I have replaced the the backlight inverter board to no avail. Same thing happens with new board in...actually a used board from ( www.myshoptvs.com )
However, with their board in, the backlight flashes briefly & then goes dark after a couple of seconds on power up.....

The power to the TV remains...green light is steady......

Seems I have a power supply board issue or a problem with the standby/audio board...but I am only guessing.....

I have access to the service manual for the chassis LC4.6U AA.....

Any leads on troubleshooting would be greatly appreciated.....

Thanks for your support in advance......

Jeff

Any suggestions for a newbie....??? Not even....."take it to a repair shop" or "buy another TV"......lol......

So anyway, i took it up to a local repair shop yesterday 2 blocks away....I went into the shop & asked as to the progress...he indicated it was my inverter board.....I indicated to him that I had replaced it with one bought off the internet, & that board performed worse....shut off after 2 seconds.....he argued that it may have been the wrong board I bought......I indicated it was the exact same board....proved it to him by showing it to him...he became quiet then about it being the inverter board and then said that he was ordering some parts for the power supply at the component level. So we will see what he comes up with.....his initial charge was $40 up front for troubleshooting....

So does anyone have any suggestions. I know someone out there has time on these models...common problem from what I have seen here.....

Any help or advice is greatly appreciated....

Jeff