TV Help wanted

[Merlin]

Help!

The TV in our lounge apparently died today. One moment it was working perfectly, the next the picture went off, but we still had sound. If we turned the TV off and on again the picture flashed for a split second then we were back to no picture but sound was present.

The TV in question is a Matsui MAT37LW507. I believe that the sound was coming through via the HDMI plug from our Virgin cable box. I can't even see the remains of a picture on the screen that may suggest that a backlight has gone, but I'm not certain as to if this set is a TFT or an LCD type.

So, what's it more likely to be, the inverter or the PSU? Powering up the TV sets it up in standby, the on button takes it out of standby and that's when we get a brief picture flash either by HDMI or Scart.

 

[johnim]

Sounds like an inverter problem as psu is powering the sound

 

[roy_bates]

inverter or backlight,if it was he power supply it probably wouldnt even turn on and come out of standby.

 

[Merlin]

Apparently it's an LCD type and I am inclined to agree that it's probably the inverter. I'm hoping that this might be cheap to buy but I suspect that it won't be.

 

[FOL]

Apparently it's an LCD type and I am inclined to agree that it's probably the inverter. I'm hoping that this might be cheap to buy but I suspect that it won't be.

What happens if you shine a torch close to screen can you see pic?
If so it will be backlight issue. Could be dodgy caps on power board.

 

[ShambleS1980]

you can change caps cant you?
inverters usually fail because the caps died..
just changing the caps usualy fixes them..

 

[FOL]

you can change caps cant you?
inverters usually fail because the caps died..
just changing the caps usualy fixes them..

Yep, done this lots of times.

 

[Merlin]

@ FOL

Nope, no picture. If I disconnect all of the cables from the TV and switch on, I get a brief flash of a snowy (tuner?) picture then nothing.

@ Shambles1980 / FOL

I haven't opened the TV up yet, that's a job for this weekend. Depending on what I see, I may try re-capping the inverter board.

Thanks for the advice.

 

[Merlin]

OK, after opening the patient up the only defective component I can see is a 4700uf, 6.3v 85C capacitor on the PSU board; the top of this capacitor is dull and domed, indicating that something bad had happened to it.

The inverter looks fine, so my plan is to replace the suspect capacitor first and see if normal service is resumed, before I look to replace the other capacitors. I'll look to replace it with a 105 or even a 125C rated part if I can.

I see a trip to Maplins on the cards... although they don't seem to stock these on their website.

 

[ShambleS1980]

strange not to see bulging caps on the inverter. its not strange that a few caps on the psu also fail. but usually there is 3-4 caps on an inverter board that are blaitantly bulging. and then a few others that look fine also need changing.

 

[roy_bates]

i wouldent bother with maplins(they have never got what you want anyway,where i am anyway)

your better off trying other sources it will probably be cheaper as well.

 

[Merlin]

Thanks to fatbob_gb, I received the replacement capacitors for the inverter this morning.

Unfortunately, after replacing them, I am no further forward.

Any more ideas as to what could be wrong?

 

[57Chevy]

I've had TVs with a "resettable fuse" that when a component goes, the fuse pops to save the (in this case the screen circuits) but resets itself when turned off. Locating the fuse and working backward from the schematics, you can locate what is overloading. Usually not caps,

 

[Merlin]

I know what you mean, they are called Polyfuses. They heat up and go open circuit, cutting the power, then they reset as they cool down. They are used a lot on modern PC motherboards.

I could do with finding a service manual for this TV now.