Friday, May 17, 2013

Repairing Proscan 40LD45Q with power supply AYL400201 - part 1


In a chain of articles I'll summarize some knowledge and experience repairing Proscan 40LD45Q LCD TV and more specifically one of its implementations.

This first article will briefly explain the main modules in the TV.

It could also serve as a generic introduction to the LCD TV family in general.

I do not pretend to be presenting you with an in-depth and detailed know-how here , let alone specific information on how to fix exactly your particular problem.

I apologize about that in advance - this is the classic problem of someone knowing too much , all of which is important and trying to teach someone who wants a small and exact portion of the knowledge right away, but is unable to describe which one - in this case because that is only an Internet blog which goes mostly one way.

Like many other modern TVs Proscan 40LD45Q is known to come with several modifications, all under the same model name. This creates confusion when it comes to supporting, because one would easily assume that the TV has this and that board inside and order replacements only to find out that the actual boards inside are different, then usually turn back and shoot at the vendor who tricked them into believing they weren't.

Beyond any doubt it will be our fault if your TV does not match the contents of this article and here in this statement we admit to that once and for all.

Take it for what it is , make most of your personal use of it (meaning: not for profit and not for distribution unless permitted by us) and if you have questions feel free to use one of the following paid resources at our site:

In these articles I will sure miss (not omit) giving some important details and will definitely not cover all possible failures. But I will hopefully get you started enough and what I'll share will be based on personal experience and as such hopefully useful to others in the same boat.

What's inside Proscan 40LD45Q LCD TV?
Before we discus problems and solutions let us quickly go through the common suspects in Proscan 40LD45Q.

Most boards inside are relatively cheaply made and that includes both design and implementation. Clearly cost/efficiency was crucial and not durability / support costs.

The list isn't complete, of course as anything existing can go bad, but definitely those are the top usual suspects:

1. Power board AYL400201 / AYL400202

     Again, there are several modifications of the TV which have different power boards inside.
     There are also AYL400203 / AYL400204 boards (also called RE46AY2501 and RE46AY2502) and there may be newer ones that we don't know of.

    This article covers AYL400201 / AYL400202 and since AYL400203/ AYL400204 are clearly very similar chances are good they will also have the same functionality , even if with some minor differences, and logically most if not all of the same problems that the original ones tend to develop.

     The power board has a built-in inverter providing high voltage needed to activate the fluorescent lamps behind the LCD with the help of the back light inverter distributor.

    Like most LCD TV power boards this one has two major modes of operation: standby mode producing only +5V power needed for the standby circuit in the main board which is capable of waking up the TV set, and full activation mode where all output voltages are produced and passed to the main board and the inverter board.

   The "standby" mode in this set is kind of cheesy in that it is actually only pretending to be "standby": half the operating voltages (+5V, +12V, +24V) are actually produced at all times, but the +12V and +24V are stopped at the board's output and not supplied to the main board until the full mode is activated. Nothing principally wrong with that other than the drop in efficiency.

  In full mode the power board can also produce the high voltage needed by the inverter board. It does that when told by the main board (there is a separate command for this purpose) and it will only work after the board has been activated in full functionality.

  On AYL400201 / AYL400202 the back light (CCFL) voltage generation circuit is separate from the other three voltage rails (+5V, +12V and +24V). If you're familiar with LCD TVs you may naturally think that the back light inverter is powered from the 24V rail, but it isn't. It is completely independent.

  The 3 operational voltages (all derived from the same transformer on the board) are all equipped with over- and under- voltage protection meaning that if output voltages start derailing too much from their designed levels will cause the circuit to turn off the connection with the load, i.e. the main board. 
It is worth noting , however, that the "cutting off" is exactly that - opening a switch (done via MOSFET transistor) to the main board; the power board itself will still continue to produce the output voltages, only not pass them to the main board).

  The CCFL output (to the back light inverter board) has a similar protection, which will turn its circuit off if it detects over-voltage or under-current (and most likely also under-voltage and over-current).

  The power board is covered with protective shield, which makes testing it a bit challenging as often times the probe may not be making a contact with an element when you might think it does.

2 Back light inverter board  CMO D022899 or AUO 19.40T02.006

  The inverter board used depends on the back light assembly used and manufactures change that based on they only know what, but one clear difference between the two is that one has 10 outputs for lams whereas the other only has 8 outputs for lamps.

  The back light inverter we've seen with AYL400201 is the CMO D022899 which has 10 outputs.

  Neither of these is a typical inverter board, actually, since the high voltage has already been produced in the power board. Still there are enough high frequency coils that could possibly go bad and maybe sometimes they do.

  It would be fair to say, however, that we haven't seen enough of those boards being bad. This observation is also supported by the very low cost and great availability for them on Internet TV chop shops.

3 Main board 9RE01ZR772LNA5-A1

The main board 9RE01ZR772LNA5-A1 of  Proscan 40LD45Q is the green one with all the inputs on it.

It takes +5V standby power from the power board, which runs a small and simple circuit , which listens for a power on button pressing or infrared power on signal; upon receiving them it sends back +5V to the small IR/LED control module this activating a small LED at the front of the TV, sends back +5V ("power on") signal to the power board and finally wakes up and transfers the control to the microprocessor, which takes it from there and runs the TV.

When the microprocessor launches it does a few essential checks (e.g. "Are all power supply voltages in range?" and  "Do all of my peer devices report they're OK?") and then starts delivering your usual TV experience.

Main boards do lots of stuff we are not about to cover here. There's a lot on that subject on Internet.

4) LCD controller (T-CON) board CMO D023960

T-CON comes from "timing controller" and this comes from the role this piece of hardware works in the TV.

Basically it takes the raster (meaning pixel-by-pixel, as opposed to vector for example where objects are described by vectors like in computer video accelerator cards) image from the main board, frame by frame and for each frame it creates the signals driving the LCD panel so that it replicates the image thus allowing you to see it on the LCD output.

Because T-CON board affects the whole screen - it barely transforms the information from raster format to serial format needed to activate the individual pixels in each row and column of the display matrix - then any defect in the T-CON usually affects the whole display and not just portions of it.

Common failures in T-CON boards are burnout of the main power supply line fuse (an SMD fuse usually close to the input cable connector), shortage of a component on the board (a capacitor or input power surge protector diode, usually located right after the fuse) or failure of an IC usually due to overheating or a shortage in the panel itself.

Next part:
Proscan 40LD45Q with AYL400201 completely dead, turns on and shuts off and other problems and repairs


Nate Davis said...

wheres the link to the next part?

world clique said...


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