Apex LD 4088 backlight shut down

[Hornnumb2]

I have this apex ld4088, the backlights will run for about 60 seconds and shut down, when they are working there is a slight buzz from inverter board. Power board is out putting the proper voltage. Standby 5v and the 24v to back light inverter board. 24v still present at plug on inverter when back lights quit. Thanks Michael

[dick_barton]

Re: Apex LD 4088 backlight shut down

One of the lamps or transformers on the inverter board may be failing. You need to look very carefully when the backlights are on to see if you have a dimmer line across the screen where a tube may be failing.

Do you still have an image on the screen when backlights fail if you shine a light on the screen and look carefully.

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Will check that tonight, I do have a led tester. I will test each strip to see what the draw is. Thanks

[dick_barton]

Re: Apex LD 4088 backlight shut down

The set uses fluorescent tubes not leds and run at >1KVolts via the transformers on the inverter board

[budm]

Re: Apex LD 4088 backlight shut down

https://www.badcaps.net/forum/attach...3&d=1601342388
Are the Inverter board mounting screws missing?
Inspect the Inverter transformers as suggested, also unplug the inverter board from the socket and inspect the inverter board fingers and the sockets.

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Ok I took the screws out to remove cover. Is there a way to check the output going to each tube? I looked that board over and didn't see anything that looked burnt. I don't have the screen off, is there anything else I can test before doing that? Thanks

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

If I were make up a led conversion kit for it, is there any reason some shorter strips couldn’t be ran vertical instead of horizontal?

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Just checked it and still have image on screen when backlight quits.

[dick_barton]

Re: Apex LD 4088 backlight shut down

Can you check the winding resistance of each of the inverter transformers and compare them to each other.
You said the set powers up briefly so are you able to see if there is a lighter band across the screen where one of the tubes may be failing?

[vinceroger69]

Re: Apex LD 4088 backlight shut down

these testers work well i have one myself
https://www.ebay.co.uk/itm/100-NEW-C...wAAOSwZ6tfRMou
this video maybe worth a watch shows how too test ccfl and also the transformers
https://www.youtube.com/watch?v=KCTVaW2XQ1o&t=1233s

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Can you check the winding resistance of each of the inverter transformers and compare them to each other.
You said the set powers up briefly so are you able to see if there is a lighter band across the screen where one of the tubes may be failing?

Which terminal do I test across in this pic? https://www.dropbox.com/s/lkcm3859pj...D4D00.png?dl=0

1 and 3?

[dick_barton]

Re: Apex LD 4088 backlight shut down

Which terminal do I test across in this pic? https://www.dropbox.com/s/lkcm3859pj...D4D00.png?dl=0

1 and 3?

It's better if you could attach any photo's to your post using Add Attachment. Dropbox wants you to sign in.

What's the inverter board part number?

[dick_barton]

Re: Apex LD 4088 backlight shut down

There appears to be 4 solder points on each transformer.
If you label them 1 to 4 then test

Transformer 1
Pin 1 - 2
Pin 1 -3
Pin 1 - 4
then
Pin 2 - 3
Pin 2 - 4
then
Pin 3 - 4

Transformer 2
.
.
.


And note the resistance carefully for each test and for each transformer 1 to 10.

It would also be worth looking on the underside of the board to see if there is any sign of overheating. Board tends to brown.

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Here is the pic, I saw one video that grounded the feedback wire to stop the shutting down. Do you know which one off the transformer is feedback?

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Ok here we go.
1) 1-2 8.45 2) 1-2 8.27 3) 1-2 8.67 4) 1-2 7.9 5) 1-2 8.67
1-3 .03 1-3 .03 1-3 .03 1-3 .02 1-3 .03
1-4 8.3 1-4 7.09 1-4 7.8 1-4 8.62 1-4 8.3
2-3 8.4 2-3 8.38 2-3 8.01 2-3 8.5 2-3 8.3
2-4 .4 2-4 .4 2-4 .4 2-4 .4 2-4 .4
3-4 8.6 3-4 8.07 3-4 8.39 3-4 8.56 3-4 8.1

6) 1-2 8.67 7) 1-2 8.1 8) 1-2 7.8 9) 1-2 8.0 10) 1-2 7.9
1-3 .3 1-3 .3 1-3 .3 1-3 .3 1-3 .3
1-4 8.01 1-4 8.5 1-4 7.8 1-4 8.2 1-4 8.0
2-3 8.4 2-3 7.9 2-3 8.5 2-3 7.6 2-3 8.0
2-4 .4 2-4 .4 2-4 .4 2-4 .4 2-4 .4
3-4 8.15 3-4 8.1 3-4 8.1 3-4 8.5 3-4 7.9

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Well I had them in columns but they didn't stay that way.

[dick_barton]

Re: Apex LD 4088 backlight shut down

Can you recheck some of your readings and were they ohms, Kohms or Megohms?
The transformers usually have a minimum of two windings on them so if one set of windings were labelled 1 and 2 and the other winding was 3 and 4 then you would expect a resistance reading of eg ohms for one set of windings and maybe 10's if not 100's of ohm for the second set of windings

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

Across 1-2 readings are K ohm
1-3 is ohm
1-4 is mega ohms
across 2-3 readings are mega ohm
2-4 k ohms
3-4 is mega ohm

[dick_barton]

Re: Apex LD 4088 backlight shut down

I'll assume that Pins 1 - 3 where it changes half way down is a typo.

The ony odd reading is T4, Pins 1 -3 @ 0.02 which could be an error in the reading but worth rechecking.

Can you also recheck Pins 2- 4 of each transformer with your meter set to ohms and post back the results.

[Hornnumb2]

Re: Apex LD 4088 backlight shut down

I'll assume that Pins 1 - 3 where it changes half way down is a typo.

The ony odd reading is T4, Pins 1 -3 @ 0.02 which could be an error in the reading but worth rechecking.

Can you also recheck Pins 2- 4 of each transformer with your meter set to ohms and post back the results.

I appreciate all the guidance, I went ahead and ordered some led strips and will convert it over. I am going to start a new thread to discuss conversion. Thanks