Ambit Backlight Inverter

[Kevin Mullins]

Just a shot in the dark here...... anyone know much about backlight inverters?
Poking around a friends little Philips TV/Monitor jobbie which started cutting on and off on them.
The video itself is working...but the backlight was cutting on and off and now finally just won't come on.
Found a couple caps that were swollen, changed those. The fuse on the inverter itself is still good. Nothing else obvious and most of what's left is surface mount stuff.

What I really need to know is what the pinout would be to verify if it's the inverter or the signal telling it to turn on.
Namely what would pin #5 be for?

8 pins total:

1 - ground
2 - ground
3 - ground
4 - has 5vDC when tv is turned on, zero when off
5 - ?
6 - 12vDC
7 - 12vDC
8 - 12vDC

It's an Ambit T501034.01 Rev3 inverter.
(but haven't found much on their stuff)

[qrz]

tv model number ?

usually there is a 25v source to the inverter.

does the fuse happen to be on pin 5 ?

perhaps only camera angle, right xformer looks as if over heated...

qrz

[MonMotha]

Lots of smaller inverters (laptop) run on 12V, not 24-25, so 12V isn't unreasonable.  Pin 4 sounds like an on-off signal.  Pin 5 may be a brightness control.  Check to see where it runs.  On some inverters, you just PWM the on-off signal, while others do the PWM onboard and have an analog signal for brightness (usually current based, not voltage).

If you happen to have a scope, easy way to see if things are churning is to look for some sort of AC (multimeter probably won't pick it up, but a true RMS might) at the input to the transformer.  They're just flyback converters, much like that found in a TV set but with lower output voltage.

[qrz]

if u get desperate     http://www.lcdrepair.us/index.html


qrz

[Kevin Mullins]

tv model number ?

Philips 17PF9936/37
One of them "FlatTV" jobbies.

does the fuse happen to be on pin 5 ?

I would have to double check, but I don't believe so. Been a day or to since I poked at it, seems like the fuse was on the 12v side of things.

perhaps only camera angle, right xformer looks as if over heated...

Yeah, that is just from a bit of shadowing.... both transformers look purty. Heck, evrything I have checked on it seems good so far. That's why I was starting to lean towards some sort of missing signal input on the unidentified pins.

Pin 4 sounds like an on-off signal. 

That's kinda what I was thinking, but just not sure.
When I try to trace it out on the inverter pcb I keep coming up to a dead end that leads nowhere. (so far anyways)(?)

Pin 5 may be a brightness control.  Check to see where it runs. 

That one I definitely have not found where it leads to on the inverter itself, so I'll keep looking.
That's one reason I was thinking of tracing it backwards and see what it was coming from off the main pcb, maybe that'll give me some insight on what it should be doing.

On some inverters, you just PWM the on-off signal, while others do the PWM onboard and have an analog signal for brightness (usually current based, not voltage).

If you happen to have a scope, easy way to see if things are churning is to look for some sort of AC (multimeter probably won't pick it up, but a true RMS might) at the input to the transformer. 

I'm starting to wish I would just go ahead and get a scope for some of this stuff. Might not use it all that often for what little I do, but man in times like this it always seems to be what I need to dig any further.

I can say that there is no signs of life from it though...... it stays stone cold, no buzz, no nothing going on.

Wondering what kind of signal I could look for on the brightness aspect with just a plain analog meter or digital meter?
Been curious if that signal was missing would that cause the inverter to basically shut down? (telling the screen to go black)

[MonMotha]

Wondering what kind of signal I could look for on the brightness aspect with just a plain analog meter or digital meter?
Been curious if that signal was missing would that cause the inverter to basically shut down? (telling the screen to go black)

Depends on the brightness control scheme.  There are several: some are analog; some are PWM ("digital") based.  The PWM based ones usually just apply a "pulse train" with varying duty cycle.  Basically, they turn it on and off really fast.  The more time it's "on", the brighter it is.  On can mean high or low, depending on design.  This rapid on/off behavior makes it tough to measure with a non RMS meter.  An analog meter on AC might respond, though the measurement would likely be meaningless.

Analog control schemes seem to usually be current sensitive.  The more current flowing through the pin (either sourced into it or sunk out of it), the brighter (or sometimes dimmer) the lamp.  On these, you can't always measure a substantial change in voltage as the impedances involved can be low.  On some designs, this "analog" input simply translates into a PWM (on/off) behavior with the duty cycle being set by the analog input on the inverter board.

Try grounding that pin, connecting it to +5V through a largeish (say maybe 1k?) resistor, connecting it straight to +5V (or maybe +12V if those don't work and you're feeling daring) in that order.  Hopefully one of those will get it to turn on if it's in working order.  Of course, disconnect that line from the TV first.

[Kevin Mullins]

Try grounding that pin, connecting it to +5V through a largeish (say maybe 1k?) resistor, connecting it straight to +5V (or maybe +12V if those don't work and you're feeling daring) in that order.  Hopefully one of those will get it to turn on if it's in working order.  Of course, disconnect that line from the TV first.

I was just on the verge of trying a couple of those combinations..... but I decided to backtrack a little first since I knew it originally would flicker and sometimes come on... and I could just tell the inverter was not on at all now.
Well, the only thing I had done was change out one cap on the main pcb and two small caps on the inverter itself. The main pcb has several of the same type and value caps, so I decided to swap out my new cap for one of those....sure enough the thing fired up the backlight. So I'm sitting there scratching my head because I know I checked continuity and such after putting the new cap in.... so I swap them back around.... the thing fired up.
What the heck is going on here?? No idea what was happening to not let it come on before. (this cap was one of the originally bulged caps, the other two were on the inverter itself)
The original caps are Rubycon 25v 470uf 85degree, the one I put in is a Jamicon 25v 470uf 105degree.
 
So it's coming on fine now, but I noticed that a lot of components are getting quite hot. Not just hot, but too hot. Small heatsinks you don't want to leave your finger on too long hot. Surface mount processors and such getting unusually hot as well in my opinion. It all seems to be working fine, volume, adjustments, channels, etc..... but I didn't want to leave it running very long because of things getting hot.
Thinking it may be something to do with the inverter again, I unplugged the inverter and let it run a bit. (blank screen obviously)
Still have stuff on the main pcb getting hot. So that tells me it's nothing on the inverter now.
Voltages still seem to be in a normal range according to the power supply and voltage regulators I've found on it.

Wondering if there are some more damaged caps causing this. (?)
This is when I wished I had an ESR meter.
Given all the monitors I mess with you'd think I'd have one by now.

BTW - pin #5 had 3.1vDC when the backlight started working again.
          pin #4 dropped down to about 4.66vDC from the 4.95v I had earlier on.
None of the pins seemed to vary when brightness or contrast changes were being made.
But then again, as mentioned by MonMotha, this just may be something I can't measure correctly at the moment. But wanted to note that a DC reading was there when the inverter is "working" so to speak.

[qrz]

the orig caps SHOULD have been 105 degree.
supply caps on the inverter b+ are common failures...

anyway, i may have a lead on the service manual .   keep u posted 
although , it likely will NOT have a schematic for the inverter
but, it should provide a connector pin out

qrz

[Kevin Mullins]

the orig caps SHOULD have been 105 degree.

Yeah, what little I have messed with these smaller TV/LCD's and laptops and such, it seems to be common practice to throw cheap caps in them.

supply caps on the inverter b+ are common failures...

I may go ahead and change all the caps in the power supply area.
But I'll have to order some first.

anyway, i may have a lead on the service manual .   keep u posted 
although , it likely will NOT have a schematic for the inverter
but, it should provide a connector pin out

That would be cool .... as I seem to be narrowing it down to having main pcb issues of sorts still. (everything running so hot has me concerned)
 

[Flashman]

Hello,

I was googling around looking for some tips to troubleshoot such an Ambit inverter.
Quite the same Philips TV set but the 15 inches one.
Sometimes I've got the backlight at once, sometimes it doesn't want to start.
Since I've open the TV it works normally (should have get afraid of the soldering station:)
So I've been able to measure the various voltage you mentionned and found the same.
A bad solder joint ? I have resoldered a lot of them.
Without scope I can't help about the brightness control system but by experience on other inverter, even without signal on this input you can get the inverter on.
Four your information some inverters IC accept both PWM or voltage control.
About your trouble, I'm quite sure the two electrolytic caps on your board are dead and I suspect the two plastic grey caps to be the source of our common trouble.
Is the supply on your TV  an external one as is it on mine ? A 12V one ? This question because I don't understand why your circuit get so hot.

Greetings from France,

[Kevin Mullins]

Thanks for joining the forum and welcome. 
 

About your trouble, I'm quite sure the two electrolytic caps on your board are dead and I suspect the two plastic grey caps to be the source of our common trouble.

I plan to change the two electrolytic caps on the inverter.
Are the two plastic grey caps you mention the square ones on the inverter also?

Is the supply on your TV  an external one as is it on mine ? A 12V one ? This question because I don't understand why your circuit get so hot.

Yes.
This TV has an external 12V power supply. It appears to be putting out proper voltage.
Still trying to figure out why everything is getting so hot though. Certainly hot enough that it doesn't seem very good.

As mentioned earlier on, if I unplug the inverter the main chassis still gets quite hot.
So that leads me to think something still on the main chassis.

[Flashman]

Hi,
 

I plan to change the two electrolytic caps on the inverter.
Are the two plastic grey caps you mention the square ones on the inverter also?

Yes. Quite an unusual package for these plastic caps but if you find some MKT type with same capacity and voltage rating it should make it.
I'm unable to read the inverter IC reference and with its datasheet it could be possible to see how it works.

8 pins total:

1 - ground
2 - ground
3 - ground
4 - has 5vDC when tv is turned on, zero when off
5 - ?
6 - 12vDC
7 - 12vDC
8 - 12vDC

Were the ccfls working at that time or not at all ? Mine were enlighted with such voltages.

Sorry but have no idea why your mainboard could get too hot. Sure you don't mix the TV supply adapter with your notebook one ?

[Kevin Mullins]

Were the ccfls working at that time or not at all ? Mine were enlighted with such voltages.

No.... this one wouldn't come on until I replaced a cap on the main pcb.
I was apparently totally missing any signal to pin #5. Once I replaced that cap I had around 3.1vDC on pin 5 and the inverter and backlights came on.
I'm sure it's supposed to be a different measurement of sorts, but that's what I could read with what little equipment I have at the moment.

Sorry but have no idea why your mainboard could get too hot. Sure you don't mix the TV supply adapter with your notebook one ?

Gonna go check right now to make sure it's the right one.
It's the one they handed me, so I just assumed it was the one that came with the tv.

Also have noticed some little "lines" throughout the image. Almost like an interference look to it. I recall seeing this when I first started messing with it and would clear up off and on as the screen would come on and off. (until the screen just wouldn't come on of course)
But now the screen comes on pretty solid, but the "lines" are there constant.
Certainly I'm still missing something going on with it....but some of them components are getting awfully tiny to test.
Just wanted to note that effect I'm seeing.

[Kevin Mullins]

Just wanted to throw a couple pics up in case anyone else is searching for this sort of thing.

The cap circled in RED is the one that kept the inverter from coming on properly.

The stuff circled in green are all suspects in need of changing even though the TV is technically "functioning". (but still running hot) Along with all the standard elctrolytics on the main pcb.

The small round black ones on the main pcb are ones I need to identify still. They appear to have what I can only describe as a circular "sweat mark" on the tops of them as if they had run hot as well. The only marking on them is a 100.

[MonMotha]

Those little gray cans marked "100" look like they could be inductors, not caps.  Tough to tell from the pic.  Check the silk on the board - C = capacitor, L = inductor.

[Kevin Mullins]

Those little gray cans marked "100" look like they could be inductors, not caps.  Tough to tell from the pic. 

Well, that would have been my second guess.... as the "sweat mark" is smaller than the diameter of the can, like it may have been a coil on the outside, but hollow towards the center.

Check the silk on the board - C = capacitor, L = inductor.

That's one thing I've noticed that is really a pain on this main pcb...... all it has are numbers.... no letter identifications for the components.
So some of the smaller stuff is really hard to distinguish as what it's supposed to be.
I should have mentioned that earlier.

Now the inverter board is clearly marked.
But also obviously coming from a different manufacturer.

[Flashman]

I've just make a little test : the 5th wire (brightness control) disconnected from the connector prevents the backlight to come on. So it is in contradiction with what i'm used to with some other inverters I have repaired before.
Well, this give a clue to where we should look and it is not the inverter (even if resoldering some joints on this board may have cure my problem).
It has run for a while now and it's amazing how hot the chips on the mainboard get.
I haven't noticed it before but the silicon can stand it better than my fingers.
I will change all electrolytics caps by 105° ones as those in place should have dried in such a tropical place.

[Kevin Mullins]

I've just make a little test : the 5th wire (brightness control) disconnected from the connector prevents the backlight to come on.

Yup, that's the exact symptom/problem I initially had with this one....nothing on pin 5 and the inverter is totally dead.

It has run for a while now and it's amazing how hot the chips on the mainboard get.
I haven't noticed it before but the silicon can stand it better than my fingers.
I will change all electrolytics caps by 105° ones as those in place should have dried in such a tropical place.

Well, at least it sounds like we are both seeing the same thing then at the moment.
One gets used to feeling things get a little hot when running.... but these things are rediculously hot. Like you said, too hot for the fingers after just a little while of running. On the verge of scary hot.

Please let us know how you make out if you get a chance to change more of the caps out.
I'll have to order some before I can go any further.
I poked around at some more voltages and such on the larger stuff I could get ahold of, but nothing seems out of the ordinary.

[Kevin Mullins]

Been doing a little capacitor moving around just because I don't have enough new ones at the moment to just go ahead and replace them. And there are 5 identical 25v470uf on the main pcb. (and I was bored)

Noticed another little oddity..... swapped the new one I have around with another and the screen was considerably slower to come on. Went back to it later on to poke around some more and it wouldn't come on at all this time.
It also did NOT get hot. Everything seemed to be of "normal" temperatures.
So I just let it sit with power on for awhile to see what it would do.
Eventually the screen finally came on after 5-10 minutes and then everything started getting hot again.

I also put the known dead cap in that spot and the screen would never come on.
So it seems there are at least a couple of those identical caps that will cause the inverter not to come on or have issues of sorts.

This also tell me some of the other caps are probably about dead and this may indeed be leading to the overheating issue. And my best suggestion at the moment would be to just replace them all.

NOTE - Also noticed earlier that any time the inverter was not getting a signal to pin 5 there is an audible ticking from somewhere around the main pcb. So this could be a clue for someone wondering if they have a bad inverter or not during troubleshooting.

The cap I'm referring to now is circled in RED.

[Flashman]

I've exchanged this morning the 5 caps by 470µF/25V/105°. It works well but since I opened it up it keeps on working and so can't really tell any difference. Maybe the OSD is more stable on the snowy image you get without an antenna connected. Anyway the scaler board still gets very hot and the OSD shows then some little flickering.
It would be interesting to look with a scope if the power adapter delivers a clean voltage
Googling with the scaler ref. LC03 i found :
http://www.grandata.co.uk/modkit71philipslc03chassispsuscalerboardrepairkit-p-7698.html
and
http://www.chsinteractive.co.uk/pdf_data/MODKIT71.pdf
The first link shows some caps references I was unable to locate on the PCB and the second one indicates that they also change electrolytic caps on the audio/tuner board.
A never ending story those bad caps. 
Hope you can repair yours as the dot matrix it is equipped with is very good and provides a really sharp image connected to a PC.
PS : the .100 are coils. You can find the coil symbol on the other PCB side.

[Kevin Mullins]

Well, it looks like both of these use the same LC03 Scaler board, so I'm assuming most will be the same aside from the actual LCD size.
I compared those cap lists and couldn't find a few of them either. I'll poke around it some more and look again. Some of the ones found on the audio/tuner board they have listed as "power supply", so that kinda threw me off a bit. I found all but 3-4 caps they have listed. They also seem to use higher voltage rated caps, so maybe they'll hold up better because of that as well.

I did some more googling and came across this though:
Philips LC03LAA Manual
Looks to have both some users manual information as well as service information that may be of some help. (I've only browsed through it at the moment)
I was able to download it, but only after registering and all that. I would just post it here, but the file is like 26MB.

PS : the .100 are coils. You can find the coil symbol on the other PCB side.

Ah, yes.... I didn't even look at the solder side of the pcb. There's no "L" designation, but it does indeed have the symbol for a coil. Thanks.
(and MonMotha was indeed correct) 

[Flashman]

Excellent!
Many thanks for the link to the service manual and, not to forget it, the help you provide.

I have reassemble mine and I consider it as repaired.
Hope you can fix yours as well.

Bye,

[Kevin Mullins]

I have reassemble mine and I consider it as repaired.

Just curious if yours still seems to run a bit hot though ?

I'm sure this one would be "fixed" by just replacing some more caps, but I was curious if that helped with the running hot issue as well.

[Flashman]

Hi Kevin,

Unfortunately not, the scaler board still gets very hot in few minutes while testing the repair.
I did not change the caps on the tuner/audio board, 'cause I'm leazy, got no more spare caps and finally presume this is its normal running condition, so can't tell if it helps reducing the heat inside.
The service manual is really well done and even provides the inverter schematic, parts list and functionnal description. But however if a 5v circuit monitor is built-in there is no clue of any thermal protection in this system.

Patrick

[qrz]

good find Kevin    had never heard of that site.

usa manuals seldom include inverter schematics      so, good to see one with it !!

still awaiting word on the manual for the provided model number......moot point now ??


qrz

[Kevin Mullins]

Unfortunately not, the scaler board still gets very hot in few minutes while testing the repair.

OK.... was just curious if it still seemed hot.
I will be making a parts order shortly, have lots of other little things I need so I'll add a bunch of caps to the list and then see what happens.
This one is currently "working" now, but still have the interference looking lines, I may try a different signal source just to see if it's any better.
And still gets quite hot. (so I haven't run it for very long)

good find Kevin    had never heard of that site.

Yeah, I was kinda surprised when I came acrossed that one.
Had to dig into the "translated" sites form other places to find it.

At first I thought it was just going to be a Users Manual when I first started browsing through it.....then I realized how big it was and kept browsing and it was surprising what all was in it.

[Flashman]

Kevin,

You now raise my own curiousity ! Will it keep on running hot or not ?
Please let me know when you get them changed.

QRZ,

If I understand correctly you wonder which model does this chassis manual on about ?
A least mine which is a 15PF9936_12.

[Kevin Mullins]

You now raise my own curiousity ! Will it keep on running hot or not ?
Please let me know when you get them changed.

I will definitely post my findings.
Probably will be a week or so until I get a parts order together.

If I understand correctly you wonder which model does this chassis manual on about ?
A least mine which is a 15PF9936_12.

Even though this one is the 17" has the same base LC03 chassis. And there is mention amongst several of the schematics that say something like "for the 15" & 17" only".
I'm certain there were like 23" versions as well, but guessing they were had different components or something.

[Flashman]

Hi,

Have you got some news ?

[Kevin Mullins]

Not yet..... been tied up on a few other projects lately.
But will get back to this one soon.