Envision TFT1780

[alegro]

I'm new at this. Its an Envision 17" LCD or TFT?
Product name: EN-7100s
Model No. TFT1780

When the power button is pressed the display flahses and there's zitt zitt zitt zitt noises, and then it shuts off. The caps look fine, but I'm no pro. It looks like maybe theres a broken copper wire or two in each of the sqaure box things. Maybe thats how they always look? I have a multimeter. Any advice on where to begin?

[PlainBill]

Re: Envision TFT1780

I'm new at this. Its an Envision 17" LCD or TFT?
Product name: EN-7100s
Model No. TFT1780

When the power button is pressed the display flahses and there's zitt zitt zitt zitt noises, and then it shuts off. The caps look fine, but I'm no pro. It looks like maybe theres a broken copper wire or two in each of the sqaure box things. Maybe thats how they always look? I have a multimeter. Any advice on where to begin?

Zitt zitt noises sounds like arcing. Possibly a broken wire to one of the CCFLs. Try it in a dark room and see if you can see any signs of arcing.

PlainBill

[alegro]

Re: Envision TFT1780

Supposing it is the CCFLs, would these be too expensive to be worth replacing on a cheap 17' monitor? Also could a beginner such as myself replace a CCFL? (I don't know what a CCFL is.)

[PlainBill]

Re: Envision TFT1780

Supposing it is the CCFLs, would these be too expensive to be worth replacing on a cheap 17' monitor? Also could a beginner such as myself replace a CCFL? (I don't know what a CCFL is.)

I was going to make some snarky comments, then realized we all had to start somewhere and you HAD posted pictures - pretty good ones at that.

1. There is a proverb - 'Don't count your chickens before they've hatched.' There is another, lesser known one - "Wanna borrow a jack?" Don't let the possibility that a repair might be uneconomical discourage you from identifying the problem.

2. Google is your friend. If you don't know what an acronym means, Google it. It will lead you to a wealth of knowledge.

3. What are your skills? Can you replace a 40 pin SMT IC blindfolded? (At one time I could - but only by handing the board and the part to Annette - a superb reworker. Today I have to have both eyes open and good light to even open up a monitor.) Can you solder? Do you believe you can get the monitor back together again?

4. The first step is to identify the source of the noise. Looking for arcing in the dark is one way. Using the tube from a roll of paper towels as a stethoscope is another. It MIGHT be a bad CCFL. Or a bad solder joint on a transformer. Or even a connector that's not fully seated.

PlainBill

[alegro]

Re: Envision TFT1780

I tried it in the dark. There was no visible arching, and no noise. The display comes on for less than 2 seconds, and then goes off. I wait a few seconds and press the power button again and same thing.

~
Google searches lead to a mass of words. They are only wealth if one understands them and knows something having read them.

[PlainBill]

Re: Envision TFT1780

I tried it in the dark. There was no visible arching, and no noise. The display comes on for less than 2 seconds, and then goes off. I wait a few seconds and press the power button again and same thing.

~
Google searches lead to a mass of words. They are only wealth if one understands them and knows something having read them.

I GET IT!!! Now do you want to try to fix it?

Hints: Measure the resistance on the transformer secondaries. Check for shorted transistors. Measure the voltage on the return lines from the CCFLs. Resolder the transformer pins.

PlainBill

[alegro]

Re: Envision TFT1780

Thank you for the hints. Will I need a schematic for this?

[PlainBill]

Re: Envision TFT1780

Thank you for the hints. Will I need a schematic for this?

If you find one, that would be great. However, you won't NEED one. Typically these problems are pretty straightforward.

PlainBill

[alegro]

Re: Envision TFT1780

Is there tutorial information on this site about how to do this?

[PlainBill]

Re: Envision TFT1780

Is there tutorial information on this site about how to do this?

There will be once someone gets around to writing it.

Seriously, fixing the 'Two seconds to black' problem isn't difficult if you have a DMM, a scope with a 2KV probe, a ring tester, a schematic, and a good working knowledge of electronics. Heck with just the DMM and a scope it would be easy. The joker is there are half a dozen different problems that can cause it and checking them all with only a DMM takes a while.

PlainBill

[ZenProfit]

Re: Envision TFT1780

I purchased 4 of this model new at the same time 5 years ago. Now one of them will not light up at all.

I noticed that the power supply LED was blinking. So I swapped it out for one of the other 3 good ones. Same problem. My local PC parts supply store believes it might be the illuminating tube, which he says only costs $10 to swap out.

Are there other threads which review repair options for this monitor? Thanks.

[alegro]

Re: Envision TFT1780

I did a little google searching but I couldn't find anything useful. My TFT1780 is still sitting in the corner because I don't have the equipment to diagnose it.

Do thesse units have good display quality and resolution? Mine was non-functioning when I got it.

[PlainBill]

Re: Envision TFT1780

I did a little google searching but I couldn't find anything useful. My TFT1780 is still sitting in the corner because I don't have the equipment to diagnose it.

Do thesse units have good display quality and resolution? Mine was non-functioning when I got it.

I noticed you indicated there was no 'zitt-Zitt' sound the last time you tried it, but it still turns off in two seconds. Take a good, clear picture of the back of the inverter and post it. You are going to have to make measurements.

PlainBill

[alegro]

Re: Envision TFT1780

Here are some photos of the rear of the inverter.

[PlainBill]

Re: Envision TFT1780

Here are some photos of the rear of the inverter.

Oh, lovely. Most of the circuitry is on the front.

On the attachment, I've marked A and B on one transformer and C and D on the other (these points are the terminals (legs) of each transformer. What is the resistance from A to B; from C to D?

I've marked the inverter controller as IC. What is the part number of that IC?

I'd like a better picture of the front of the inverter. Say from the yellow line all the way to the right hand end. (This is necessary only if the resistances match one another.

PlainBill

[alegro]

Re: Envision TFT1780

The resistances for both A>B, and C>D are 0.L

The IC part number is:

23A8RVK
TL1451A

If you still need the photo of the top let me know.

[PlainBill]

Re: Envision TFT1780

The resistances for both A>B, and C>D are 0.L

The IC part number is:

23A8RVK
TL1451A

If you still need the photo of the top let me know.

Shoot!!! This may be getting more interesting. 0.L would be 'out of range' or 'off scale'. What range did you have the DMM on? I would have expected a resistance of around 1000 ohms; perhaps I should have mentioned that.

If both transformers read 0.L on the 20K range, try measuring the resistance from point B to each of the 7 pins on the other end of the transformer. And do the same from point C on the other transformer.

No need for pictures yet.

PlainBill

[alegro]

Re: Envision TFT1780

For the A>B, and C>D readings (yesterday) I had it on Autorange.

Today I got out-of-range readings on A>B, and C>D no matter what setting I had it on.

B to each of the first 6 pins were ~19.7 K ohms

the 7th pin (closest to the edge of the invertor board) was 0.4 K ohms

- - -
C to each of the first 6 pins were ~18.9 K ohms

the 7th pin (closest to the edge of the invertor board) was 0.4 K ohms

(I did these readings on the 00.0 K ohms setting.)

[PlainBill]

Re: Envision TFT1780

For the A>B, and C>D readings (yesterday) I had it on Autorange.

Today I got out-of-range readings on A>B, and C>D no matter what setting I had it on.

B to each of the first 6 pins were ~19.7 K ohms

the 7th pin (closest to the edge of the invertor board) was 0.4 K ohms

- - -
C to each of the first 6 pins were ~18.9 K ohms

the 7th pin (closest to the edge of the invertor board) was 0.4 K ohms

(I did these readings on the 00.0 K ohms setting.)

Repeat the 'B to 7th pin' and 'C to 7th pin' measurements with the meter on autorange. I want to see if there is any difference between the readings.

PlainBill

[alegro]

Re: Envision TFT1780

On autorange:

'B to 7th pin' was .438 K ohms

'C to 7th pin' was .437 K ohms