# Polaroid 40" LCD red LED help



## digiguy12 (Dec 27, 2009)

So my 40" Polaroid (4011-TLXB) stopped coming on and now when i plug it in I only get a solid red light. I took it to a TV repair shop and the idiots wanted $500 to fix (more than it's worth new). They said the "control box" needed to be replaced. They control box included both the power supply and the main board/tuner. There are no obvious bad caps or burns anywhere. I don't want to put too much into this so want to replace just ONE of the two boards in hopes that will fix it. So which do you think it is, power supply board or main board? 

Should I replace the Big 150uf 450v capacitor eventhough it doesn't look bulged or leaking? when i plug it in a "charge up" sound comes from the power board. Thanks guys. I hope I don't have to trash this LCD.


----------



## octaneman (May 13, 2009)

Hi digiguy12

You will have to perform tests on both the power supply and inverter before you decide to replace any of the boards. Testing capacitors is not an exact science because even though it may look good on a capacitor meter, it still could leak as it heats up. Doing a charge rate test (timing the capacitor when it charges/discharges) can offer some insight to intermittent faults but testing the surrounding diodes ( zeners especially) and resistors are equally important.

My advice is if you're handy with electronics, get a schematic and check your outputs from the power supply. If all goes well then you can be confident which boards will have to be replaced.

post back your findings.


----------



## digiguy12 (Dec 27, 2009)

thanks for the suggestions. Unfortunatly, I cannot find the schematics for this model that is clear enough to read. I even went to the Polaroid website and downloaded the service manual and it's too blurry to read. Any ideas where I can get a clear one from?


----------



## octaneman (May 13, 2009)

Here is the manual : http://www.polaroidsupport.com/pola...LXB-4011_TLXB-4241_ServiceManual_20070613.pdf



There is an active flow chart with complete wiring diagrams which shows which pins to look for, but it maybe the same file you have. I can see the chart but the wiring diagrams are fuzzy when enlarging the image. Try saving the diagram and look at it through a different viewer.


----------



## digiguy12 (Dec 27, 2009)

yeah, that's the repair manual I already have. I can't read it enough to test properly. I have checked the voltage throughout and it seems to be getting voltage to the input on the power supply and 10.2 volts on the output of the board. Inverter board also seems to be getting 52volts on all power wires. I'm thinking it's the main board somewhere. I really need to get a in-circuit capacitor tester, but they are around $200.


----------



## digiguy12 (Dec 27, 2009)

also read, that it's a circuit on the main board that causes it to turn from standby (red) to on (blue). So my best guess is it's the main board. I can get a used one for $60, so maybe i'll go that route and take the gamble.


----------



## digiguy12 (Dec 27, 2009)

Well, I had a friend who has a broken 42" polaroid lend it too me. The power sources were different, but the main board was 99% the same (had a different rev. letter and like 1 extra part). On ther 42" set, his problem was that it came on (blue light), screen came on for a few sec., then went to black.

So i swapped out the main boards since they connected the same way and the 42" board turned on the 40" board this time (went to blue light), but tons of vertical lines appeared so i'm guessing it is just the wrong exact main board (one was 42" 1080p, the other 40" 720p). This basically ruled out that the power source was bad on the 40" and just needs the correct main board. 

Looks like the power supply is bad on the 42" also. Wish they had the same power supply to swap. But looks like i'll be getting a new main board for the 40" and a power supply for the 42" (still nothing looks wrong on the 42" power board, no leaking caps). put the 40" main board on the 42" and no blue (just like on the 40"). 

I hope this goes well, lol.


----------



## digiguy12 (Dec 27, 2009)

ok, maybe even better news. the 42" that comes on w/ blue LED, then goes black has a slight bubble on the BIG capacitor on the power supply. Very hard to tell as it's not a metal top, but a plastic top. It's very slightly bulged. it's a 220uf 450v 105 degree cap. I'm going to try and replace this one and see if that fixes it


----------



## octaneman (May 13, 2009)

The best method to troubleshoot this problem is go through the flow chart and locate the circuits manually. It will be a hassle because it will take you longer to locate the circuit one-by-one. But you will be able to test the proper pins it recommends without second guessing.


post back your results.


----------



## digiguy12 (Dec 27, 2009)

I didn't see a flow chart that was legible in the manual. Everything was too blurry to read at all once it got to schematics. I ordered a 220uf 450v capacitor for the 42" and will probably get a main board for the 40".


----------



## Done_Fishin (Oct 10, 2006)

Those large smoother caps "bulge" because the sleeving is heat-shrink tube which shrinks even more as the caps heats up. This places tension on the plastic cover, causing the bulge. I have seen many in what look like Bulge condition, except for the fact that when you remove the plastic (it's only a protective isolation due to the possible voltage on the metal can) the can is totally flat underneath. 

For the price of a new capacitor though, you will at least have peace of mind when you have replaced it.


----------



## digiguy12 (Dec 27, 2009)

thanks for that info. I ordered the part for $8 shipped, so it's worth the try.


----------



## digiguy12 (Dec 27, 2009)

replaced the main capacitor and no luck. I'm getting 120volts in the power supply, but zero out of it, so there's something that's gone bad. I don't have the proper testing equiptment (only a multimeter) and knowlege to try and fix the power supply board. I will either just sell it as is, or I may buy the $100 power board. Not sure if it's worth it yet.


----------



## Done_Fishin (Oct 10, 2006)

What IC's are in the area of the Power supply on the primary side ?

Look for the IC, also look for a transistor like device that says 431A or similar - might be LM or TL but it will more than likely be TO92 and have 3 legs or it could be an smd version with 8 legs.

the 431 is a voltage reference device used for comparing a voltage against a known value.

There will be a switch mode controller IC, one of many types and styles. You will have to note the device name and Google for it to see if its the one. There are probably a couple of electrolytic caps near it which are part of the bootstrap / delay for the IC to function. I'd replace the 431, the caps and then the IC looking for the problem.

Also check that there are no open circuit windings in the transformer and no shorts on the secondary side of the transformer that would stop the switch mode from working.
Note that the diodes frequently used on SMPS secondary side could be Schottky types with ~0.2V forward bias as opposed to conventional fast diodes

EDIT:
Is the red led powered from the secondary side ? This would indicate that the power supply is working.

Check your Voltage rails, maybe one is missing or is low voltage.


----------



## digiguy12 (Dec 27, 2009)

here is a link to the exact power supply board (exact part number, eventhough it says it came from a 40" model). What should I be checking besides all the capacitors? I'm not very familiar with all the parts and how to check them as I only have a simple multimeter.

http://photos.discount-merchant.com/photos/1028/photos.php?itemid=1110820


----------



## Done_Fishin (Oct 10, 2006)

There's not a lot to be said from that link you gave
There is an Integrated Circuit (IC) in the middle of the board that is probably the controller. There are other SMD IC's under the board along with what might be a few transistors & Diodes

there is also a 3 legged transistor or IC to one corner, might be the 431 I was talking about for Voltage reference.

Without knowing more about the board and a photo of the board is about as much use as a photo of a prospective girlfriend, just gives an indication as to what it looks like, no idea though what it does or how it does it!

Give me some more details about the board. The name of the IC for example so that I can figure out what is going on.

What I can tell from the photo's.

Switch mode power supply.

Opto-couplers in the feedback circuitry helping to control the secondary Voltages. Probably means that the reference voltage is on the secondary side and that all voltages are controlled according to the value of one VOLTAGE RAIL .
One Opto couplker will be sending back information from the voltage comparator, the other may be sending back information about over-current or over-voltage or whatever the designer considered was his priority at that time.

There is a second IC with a green sticker on it, about which I have no idea what it could be doing.

How do these circuits work?
The incoming AC Voltage is converted to DC Voltage by a bridge rectifier and then smoothed with that Big capacitor to provide both a stable Voltage and a current reservoir in the event of temporary loss of incoming AC.

Somewhere a bleed resistor will allow the DC Voltage to supply a minimal current to the SMPS Controller IC. When the Voltage exceeds a certain level, the Controller IC will send pulses to a transistor which will create changes of Voltage in the transformer. These changes will result in secondary voltages, which will be rectified and smoothed to feed the rest of the equipment. 
From one or more of the secondary voltage rails, a resistance feed will compare the output Voltage(s) with a reference voltage and the result of the comparison will be fed to an opto coupler. When the voltage is more or less correct a voltage level will be sent to the controller IC to stop generating pulses. If the Voltage goes below a certain threshold the signal sent will be to start or increase the frequency of pulses.
In the event that the controlling circuit does not gain a proper response it will automatically shut down. Extra sensors can be included to detect current overload, Voltage overload and / or insufficient current being drawn, to name but a few.

trouble shooting a switch mode power supply is extremely difficult since there is feedback from one side to the other and at any one point that a fault occurs everything stops or should do. If it doesn't stop by use of electronic safeguards it may well stop due to the ensuing explosion as something goes "POP". I have seen the results of many such incidents, usually resulting in blackened fuses, missing transistor bodies and also on several occasions, missing tracks.

working on mains input switch mode power supplies is dangerous and tricky. I cannot stress this enough. You need to isolate yourself and the smps from EARTH potential should you decide to start poking around with a multimeter when the power is on.

Check resistors for correct values and that they are within tolerance. Most resistors that are standing "off the board" can be considered safety resistors. Measure them by unsoldering one side and isolating it from the board.

That's enough for now .. try getting a service manual with a decent legible diagram.


----------



## digiguy12 (Dec 27, 2009)

I think i've gone too far in trying to fix the power supply as I don't know enough about electronics. I do know enough that if the two output wires (two white ones in those pics) are not getting ANY voltage when plugged in, means the board is bad. Went ahead and bought a used (but tested good) power supply. I hope it fixes the problem. At least i'll have an extra board for parts if the new one goes bad.


----------



## Done_Fishin (Oct 10, 2006)

Good Luck. Sorry I couldn't be of more help.


----------



## digiguy12 (Dec 27, 2009)

thanks. No, you were a big help. You really know what you're talking about, so much that I am lost:laugh:. I am not an electronics person. I am a mechanical engineer and understand how things work and move, so electricity is not my strong suit. I'll keep you guys updated on how it goes.


----------



## machx0r (Jun 2, 2010)

Sorry to hijack an old thread but I'm wondering if someone who downloaded the service manual linked above could repost it somewhere. I get a 403 Forbidden when trying to view the file.


----------

