Digitrex CTF4071, Sound but no picture

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Tom,

Thank you for the advice, I will measure BLON and ON/OFF. How do I test the transformers? Am I able to test for a bad bulb?

Andy

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Tom,

ON/OFF is a constant 4.7v, I cannot find a pin BLON, where is that on the connector/PCB. I have also checked the other voltage on the connector on the PSU/Inverter there is a +12v that is reading 11.2v, is that close enough?

I will measure the transformers next if you think its worth it if so not sure how to measure them, if powered up etc..

It the same again switched the set on after being off for a few days image comes up for about 1 minute and then no picture but sound.

Andy

[tom66]

Re: Digitrex CTF4071, Sound but no picture

ON/OFF == BLON
Also there should be a DIM pin check this
Not sure testing the transformers is worth it -- you might not be able to buy them - what part # is on them?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

OK, So measuring ON/OFF is the same as BLON?

Sorry I do not know what the DIM pin is, I have checked the PSU but cant see pin/post or anything on any of the connector, just:

GND,GND,SW,+5VSB,+5VSB,+12V,+12V,GND,ADJ,ON/OFF,GND,GND, +5V, +5V

GND, GND, +24V, +24V


The upper transformer is AYL401401 T101F AY101002

The lower transformer is AYL401401 L1O4F AY100602

[tom66]

Re: Digitrex CTF4071, Sound but no picture

Ah yours appears to have ADJ = DIM. Controls brightness of backlight. If set too low, backlight might not stay lit.

Yeah ON/OFF and BLON are different names for the same pin, both control backlight on/off.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Great I am learning even more so thank you loads,

Just measure ADJ/DIM.... 4.96V.

I powered off the set and switched back on and the display came on for about 15-20 seconds, again no picture but sound.

I also powered it off for a few minutes and measured DIM and it was 1mv, I then switched the set on at the wall (still in standby, red light) it jumped to 4.95v and after a few seconds dropped to approx 30 mv and stayed at that, I then switched it on from the front button and it went back up to 4.95v. The display came on slightly longer about 1 minute.

Andy

[tom66]

Re: Digitrex CTF4071, Sound but no picture

At the point of the display switching off, were both DIM and the BLON the same or nearly the same?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

BLON was flutuating between 4.61v- 4.85v. At the point the display went off it prob changed by 0.01v.

I then switched the set off and on and monitored DIM that was the same changed if at all by 0.01v at the point the display went off.

Andy

[tom66]

Re: Digitrex CTF4071, Sound but no picture

So, the problem is somewhere on the inverter board.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

OK, Do you think I coud get it to component level or will it be a PCB replacement?

[tom66]

Re: Digitrex CTF4071, Sound but no picture

Not sure if bulbs or power/inverter board, hard to tell without taking panel apart.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

OK, so if I dismantle the actual panel, will it be obvious if its a bad bulb? is it a fairly easy strip down? I am very competent at mechanical things.

Or is there anything else I can measure on PSU/Inverter?

Andy

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

PS- If I you think its not to long a job to strip panel is there any info on best was to do it? from front etc.. also if I find a bad bulb can they be purchased?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

I have seen the PSU/Inverter on ebay for £60 plus postage.

[tom66]

Re: Digitrex CTF4071, Sound but no picture

Terrifying to strip a panel down. You need to take the LCD glass out of the set, and put it on a cloth/padded surface. Need 2.5x size of TV to work on and be very careful with the LCD glass, smudges cracks etc can be very bad.

Take the front plastic bezel off, then the metal frame off the panel, then disconnect t-con connectors etc and lift LCD glass off. 3mm thick 40 inch sheet of glass is the panel itself and the critical part. Then remove diffuser layers to access bulbs.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

OK, Doesnt sound to bad at the moment I will give that a go tomorrow, sorry for an other question, will it be obvious if a bulb is causing the fault? can they be purchased?

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Hi Tom,

I am going to attempt the strip down tomorrow first thing, but before I do I want to check:- what a bad bulb will look like? also can I buy bulbs if I find one that is faulty??

If you cant then I wont bother to strip it down.

Andy

[tom66]

Re: Digitrex CTF4071, Sound but no picture

A bad bulb will be unlit or only flash briefly.
A bad transformer will show as multiple bulbs unlit corresponding to one transformer only.

[Andyd1970]

Re: Digitrex CTF4071, Sound but no picture

Ok thank you for the info, but the key question is are the bulbs available as spare parts? as no point stripping it to not find the parts are available.

[tom66]

Re: Digitrex CTF4071, Sound but no picture

Usually, but expensive, around £20~£40 each.