Digitrex CTF4071, Sound but no picture

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi,

I am happy to test the transformers, would appriciate a bit of advice on how and what I am expecting to see, also test them powered or not?

[signup]

Re: Digitrex CTF4071, Sound but no picture

Do you have a pic of the underside of the board, and test them power off

[tom66]

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.

Personally, I use an ESR60, but that's around £70 so quite an investment. I've heard some good reviews from the £20~£30 meters though.

[budm]

Re: Digitrex CTF4071, Sound but no picture

The two red poly caps are part of the Bridge drive circuit, need to see the bottom side of the board to see for sure.
I think this is how the board is setup, not sure until I see the bottom side.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Guys, Thank you so much for your help with this, learning alot more now, the guides from the last post are very helpful, thank you.

See attached pictures of the rear of the PCB.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Guys, Are the images of the rear of the PSU/Inverter close enough? do you need an areas zoomed in on?

Andy

[budm]

Re: Digitrex CTF4071, Sound but no picture

I just download them to study, will let you know later on today.

[mardocdor]

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

Hi just wander if you tried putting a flashlight infront of the screen and look if you can see any faint image?

[budm]

Re: Digitrex CTF4071, Sound but no picture

I hate to tell you this, it looks like you pull the lamp's socket assembly off the lamps. I think the socket assembly should not be remove, the board has fingers that fit into the lamp socket assembly and should just slide out. I hope I am wrong, otherwise you may have broken the lamps when you remove the assembly or when you try to put the board assembly back in place since you have to make sure the lamps will all fit back into the lamp sockets.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi, I think you are right I thought that when I removed the PCB as it was soo tight in the small sockets it made sense to remove the black plastic part, I have just tried refitting it and it all sounded good as it when back on, switched it on, I have an image but faint! so I guess its f++ked then?? Is it pissible to refit that part? or is it a waste of time?

Kind regards
Andy

[budm]

Re: Digitrex CTF4071, Sound but no picture

So the lamps stay on, or it still black out after 2 seconds? This is what the SCH I draw based on your pictures.
Not sure if the lamps are damaged or not, or if they are fit back in to all sockets, but you should check the resistance on the HV side of the four Inverter transformers.

[tom66]

Re: Digitrex CTF4071, Sound but no picture

What confuses me Bud is the inverter looks to be on the secondary side and only have those poly-capacitors coupling the signal across?

[budm]

Re: Digitrex CTF4071, Sound but no picture

They are on the primary side, all gorund shound in the pictures are the primary side ground, the coupling caps to ground is needed to block the DC. Isolation from primary to the lamp connections is done through the inverter transformers.
You can see about the same setup in the SAMSUNG Inverter/power supply setup, very common way of driving the Inverter transformer with 380VDC. Think of it as audio power amp with push-pull output running with single power supply, the midpoint will be 1/2 B+, so the speaker will have be hooked up through cap so the speaker will not blown up by the DC at the center point of the output.
http://sound.westhost.com/project12a.htm

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Guys, You wont believe this but I managed to refit the black plastic assembly to the ends of the lamps, switched the set on and the entire screen illuminates!! and now I get a picture, (the sort of home screen image) I will give it an input in a minute and report back. Do you think it could be cured?

Andy

[tom66]

Re: Digitrex CTF4071, Sound but no picture

May have been a loose connector on the bulbs.

[budm]

Re: Digitrex CTF4071, Sound but no picture

It does sound like that was the problem, you are so lucky that you did not break the lamps.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Thank you guys for all your help and support, it was a lucky fix.

Andy

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture, failed again

Hi Guys, Bad news (( put a DVD on and the picture comes on for a few minutes and went off! switched it off from the button on the front, switched it straight back on and it worked for about 30 seconds and the image went, but the sound was working fine.

Heeelllppp!

Andy

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Guys, Tried it again today and it did the same screen comes up with the home screen, put on a DVD played for a short while, screen went off and still had sound.

Any ideas please?

Andy

[tom66]

Re: Digitrex CTF4071, Sound but no picture

BLON or ON/OFF steady?
Likely bad bulb or transformer.