Digitrex CTF4071, Sound but no picture

[Andyd1970]

Hi Guys,


Hope you can help, I am OK with a meter and soldering so that should be some relief for you

I have a Digitrex CTF4071 that has sound and no picture. I have attached some pictures of the sets internals, has a very odd PSU/Inverter??.

So far I have checked the fuse on the T-CON also the fuse in the PSU is OK.

So far Tom66 has been a star and I have manged to fixa few friends TV's with out his help due to the technical fault finding tips, but as this has a conbined PCB I thought I would see the best way to tackle it.

[budm]

Re: Digitrex CTF4071, Sound but no picture

That looks like MAGMEET power supply/inverter combo. I cannot read the model number on the board. Tom may have the service manual for this board. Are the backlights on?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi,

The back light come on for a few seconds and then goes off.

The info from the combined PCB is:

AOYUAN
AYL401401
3BS008114 Rev 1.0

[tom66]

Re: Digitrex CTF4071, Sound but no picture

You have "2 seconds to black".
Check the pin voltage BLON or ON/OFF, on the connector from the main board.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

I just switched it on and the picture came up!!

I switched it off and again the back light came on for a few seconds and then nothing.


ON/OFF - 4.7v on the connector from main PCB

Did notice the 12v taking a reading of the connector on the inverter/PSU is 10.7v.

[tom66]

Re: Digitrex CTF4071, Sound but no picture

When the backlight is on, is the 12V higher? Like closer to 12V?
You probably have an intermittent bulb or transformer.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

I have 12.2v ish as soon as the set is switched on pressing the switch on the front, when the back light comes on it drops to about 10.4v and when the back light goes off it stays at 10.4v.

[tom66]

Re: Digitrex CTF4071, Sound but no picture

You may have some bad capacitors on your power board. Can you get a closer image of the power board, perhaps broke into several parts?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

I did look for any domed or leaking caps but could not see any obvious, I remember you saying they do not have to be leaking to be bad

[tom66]

Re: Digitrex CTF4071, Sound but no picture

What voltage do you measure across the CAPXON 450V capacitor?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

389V plus or minus a few MV.

[tom66]

Re: Digitrex CTF4071, Sound but no picture

Is there a 24V or 5V pin?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Do you mean as an input to the PSU/Inverter? there is a large connector, top of the first pic that comes from the main PCB.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Just checked the voltages on each pin and they are as shown apart from the 12v which as I said drops to 10.4v once the back light is on and goes off.

[tom66]

Re: Digitrex CTF4071, Sound but no picture

I would suggest recapping the entire board, because there may be a bad capacitor on it. Difficult to tell. If the 12V is used for the inverter that may be the fault (even if it is only used for the logic side of it.) With an ESR meter you could check them and verify them as good or bad.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Tom,

Can you recommend an ESR meter? I have seen some for over a hundred to ones from China for about £20. 00.

[budm]

Re: Digitrex CTF4071, Sound but no picture

The inverter circuits on this board runs off the 380V, you cam see the GATE DRIVE small transformer next to the samll blue cap and the large transformer.
Can we see the bottom side in 1/4 section or more so we can trace the connections?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Budm, Do you mean the two transformers on pic 2? when you say bottom side do you mean the underside of the PCB?

[tom66]

Re: Digitrex CTF4071, Sound but no picture

I am not sure. It looked isolated to me Bud, but then the large red poly capacitors across the gap may be coupling the drive signal.

[signup]

Re: Digitrex CTF4071, Sound but no picture

Hi. sorry to jump in but have you took readings from the transformers, I had one of these and the tranny's were bad, I have also seen those types of transformers go down in a few tv's now