AMW M177TD switches off after a while

[_max_]

Hi friends,

this LCD panel has affected by an annoying issue: it works normally as soon as has powered on, but unfortunately it switches off after a random time (few minutes, tens minutes max). Once powered off, it switches on but remains ON for a short time more and more.

I thought bad caps, but unfortunately all of them look quite good despite of the age (jul 2005).

Here there are a couple of photos of the mainboard I have got today.
Do you have any suggestion on how to try to fix it?

[_max_]

Re: AMW M177TD switches off after a while

I am sorry but I made a mistake with on line pictures.
Is it possible to edit the message?

[paulstef]

Re: AMW M177TD switches off after a while

Doesn't sound professional, but believe me the easiest thing to do is to heat the whole board until it does not power on anymore. Do not cook it, just heat it up with a hair dryer or heatgun without burning anything of course. 60C to 70C is ok. Then take cooling spray and spray part by part until it comes on.

You can easily narrow down the problem to a certain area. Could be a lot of things, start with this first.

[_max_]

Re: AMW M177TD switches off after a while

Interesting. I will try soon.
Thanks for your suggestion

[_max_]

Re: AMW M177TD switches off after a while

One question:
what does the white glue (or silicon compound or whatelse) deposited on some components ?

[paulstef]

Re: AMW M177TD switches off after a while

A force exerted on the solder joints can cause them to become loose (break, crack) over time. The component that are glued are usually higher/bigger/have more mass than others. The glue helps to decrease this effect of vibration.

Don't know how much sense it makes in a rarely moved TV set. It is very common in automotive electronic components.

[budm]

Re: AMW M177TD switches off after a while

One question I have is that when it goes off, it goes into standby (like when it does not see video signal from the PC) or it acts as if the power switch is activated? We use the glue during wave soldering, some component will try to float up off the board.

[_max_]

Re: AMW M177TD switches off after a while

One question I have is that when it goes off, it goes into standby (like when it does not see video signal from the PC) or it acts as if the power switch is activated?

Thank you for your answer budm.

Unfortunately I have not the LCD in front of me now.

So far as I remember (but I will do a deeper check tomorrow) when the display goes off (say 10 minutes after powered on) it switches off the display (black image on the screen), even if the main led remains ON. Pressing the power button does not help if done immediately after, one has to wait for a while before powering ON the display again. Then the failure happens earlier and earlier.

[_max_]

Re: AMW M177TD switches off after a while

It looks to me that the problem is related to the inverter section.

The display light switches off quite soon now, the power led remains green (normally it is OFF when unplugged or orange when there is no video signal) but I can see images on the dark screen by using a torch.

So I have dismounted the mainboard but unfortunately I have no experience enought to find by myself the issue.
All the caps look quite good to me, now I am going to look for open diodes/transistors/fuses (but this sounds strange because of the display works at the very beginning).
Unfortunately I am unable to find the schematic diagram of this model (AMW 177TD), so I don't know which PWM/switching component could be damaged and how to check them.

I am quite sure that someone very experienced here by looking into photo details, can find the bug. I am still too young :-)

Any help would be very appreciated.

[wobbin]

Re: AMW M177TD switches off after a while

It's a bit hard to tell from the photo as I can't quite get close enough, but is the casing damaged at all on the transistor marked Q40 on the underside of the board ? If so it's where I'd be looking for a shorted or open circuit device which would certainly cause the backlight inverter to trip out.

It may just be my dodgy eyesight ;-)

Cheers
Robin

[_max_]

Re: AMW M177TD switches off after a while

Thanks Robin.
I will check Q40 more carefully tomorrow then I will be back.
If was the Q40... How can I get its specs without the schematic?

[paulstef]

Re: AMW M177TD switches off after a while

Take a better picture of the 4 transistors including Q40. They are probably the same or complementary. We need to know what is printed on them From the code printed and knowing it's a bipolar transistor in a SOT223 package we may find out what it was.

[_max_]

Re: AMW M177TD switches off after a while

There was dusty on that transistor.
Measured with an ohmmeter BCE and it reads about 0,6 kohm and 2,1 kohm direct polarisation and >10kohm inverse polarisation. All the four BJT reads exactly similar values, so it is difficult to believe that all of them are burnt.
On Monday I will get a better picture.

[Rtech]

Re: AMW M177TD switches off after a while

The symptoms sound like intermittent failure of a Backlight,you really need a spare pair to test.I recently had the same thng on a Tv.

[_max_]

Re: AMW M177TD switches off after a while

Do you mean another LCD panel?

[Rtech]

Re: AMW M177TD switches off after a while

No, a set of working lamps to test yours.

[niky59]

Re: AMW M177TD switches off after a while

Hello anyone has lon wiring diagram for this monitor?

[stj]

Re: AMW M177TD switches off after a while

could be the tubes,
but i'd start by re-soldering the invertor transformers.

but 9 years old is a long time
if the tubes are gone, i'd fit an led replacement kit.