Acer AL1914 Power Light on No Display

[ZappedAgain]

Let me start by saying thanks for this wonderful resource. I have managed to repair half a dozen monitors with help from the site.

I think I have a bad transformer on the inverter board but I want to try and confirm this and maybe find a source for a replacement.

The monitor power light will turn on and off with the switch but I see nothing on the display. There is no image even with a flashlight.

I have proper 120v in and can measure 165v across the largest cap on the board.

I am measuring 79v on one side of the transformer and nothing on the secondary side. I am also showing no output voltage going to the other board in the monitor.

the numbers on the transformer are DG100017200 YUVA 0520

Is my assumption correct that the transformer is bad or can something else cause these measurements?

[retiredcaps]

Re: Acer AL1914 Power Light on No Display

The monitor power light will turn on and off with the switch but I see nothing on the display. There is no image even with a flashlight.

Is my assumption correct that the transformer is bad or can something else cause these measurements?

If your power led comes on and off by hitting the power switch, that implies that your power supply and main board are likely good.

If you are not getting a display (not even a brief flash of backlight), that implies the mosfets (Q904, Q905, Q906, and Q907) on the backside are possibly shorted.

To test them, see the section on mosfets at

https://www.badcaps.net/forum/showpo...4&postcount=19

[ZappedAgain]

Re: Acer AL1914 Power Light on No Display

I reconnected the board to the monitor and I was able to get the acer logo displayed once for about 1 second. turning the monitor off and back on did not bring it back again.

I will recap the board and if this doesn't do the trick I will follow your instructions for 2 seconds to black and post the results.

Thanks and sorry to have wasted your time

[budm]

Re: Acer AL1914 Power Light on No Display

If you can see that the power LED is on then the power supply is working because the 5V and the 12v are generated from the same transformer.
Please take some readings per attached pictures.
Also, do you have test lamp for inverter testing?
Otherwise look here:
https://www.badcaps.net/forum/showthread.php?t=19987
We need to know if the lamp even flash for a second or not.

[ZappedAgain]

Re: Acer AL1914 Power Light on No Display

Ok the results of My Testing.

1. The monitor will display the acer logo for a fraction of a second when first plugged in and turned on. Will not if you turn the monitor off and on with the switch. Power light does go on and off with each press of the switch.

2. 5VDC for Logic is Present 5.17VDC

3. 12 to 18vdc in Picture 1 shows 19.1VDC

4. Resistance between top two points is infinite. (Meter is on correct Scale)

5. Resistance between bottom two points is infinite.

6. Voltage measurements for the three points in Picture2
-----ON -----------OFF
Top--5V -----------5V
Mid-- 3V-----------0V
Bot-- 5V-----------5V

Thanks

[budm]

Re: Acer AL1914 Power Light on No Display

OK, your power supply is fine, and the control signals are fine. The strange things are that both high voltage winds are showing open! It does look like you have open windings, may be look real close at those solder joints just to be sure they are not bad.

[ZappedAgain]

Re: Acer AL1914 Power Light on No Display

rechecked the continuity and get the same readings. I am able to see the leads on the top side of the board and get the same reading there as well. I did get continuity between the two middle pair of the transformer. Bad Transformer?

[budm]

Re: Acer AL1914 Power Light on No Display

Can you read the P/N on the top of the transformer, then we can look up the wiring for sure. So far it does look like bad transformer unless some one else has other suggestions.

[selldoor]

Re: Acer AL1914 Power Light on No Display

This doesnt make sense.

"The monitor will display the acer logo for a fraction of a second."

1 For you to see that the back light must have flashed on.
2 For the back light to flash on the inverter transformer
must have worked. at least on one side

Please can you test your multimeter - new battery? check probes.

With a piece of emerypaper rub the joints on the transformer until shiny then with meter on 2000ohms re test. The leads on top are often laquered so dont conduct.

Have you another monitor so you can test the ccfls and also
use the panel to test this one.
Can you get to the ccfls to see what the wiring/ends look like.

[budm]

Re: Acer AL1914 Power Light on No Display

That is the part I do not think will be possible either unless it arcs over the open connections in side the transformer, but both windings?. May be something is not measured correctly, that is why I want to look up the transformer spec.

[selldoor]

Re: Acer AL1914 Power Light on No Display

@budm label says DG100017100 -think the rest is not relevant?
T2401A2830520 cant get any hits on that bit. Cant find much on first bit either - perhaps you have more luck

[ZappedAgain]

Re: Acer AL1914 Power Light on No Display

Ok switched the meter to the 2kohm setting instead of 200 and I am reading .5 k ohms.
On the 200 ohm setting it shows no continuity. If I touch the leads together on the 200 ohm setting it shows less than 1 ohm.

I will see if I have another working monitor I can test the CCFL's and Panel

[ZappedAgain]

Re: Acer AL1914 Power Light on No Display

Transformer Part No is DG100017100 / T2401A2830520

[selldoor]

Re: Acer AL1914 Power Light on No Display

ok .5k is better than open but not accurate enough please retest and post as follows
Inverter transformer resistances
Top two as per budms pic xxx ohms
bottom two as per budms pic xxx ohms

Please can you also update your profile with at least country and mains voltage.

[budm]

Re: Acer AL1914 Power Light on No Display

OK, should have asked what scale he was using to read the resistance.

[ZappedAgain]

Re: Acer AL1914 Power Light on No Display

More Accurate Transformer Readings. Meter Scale set to 2k

Top transformer Pair .566 k
Bottom Transformer Pair .569 k

Tested all of the mosfets on the Back for shorts.
All the three Pin mosfets show no shorts

U801 however shows a short between pin 1-4 and pin 6
Part Number of this chip is SG6841SZ

[budm]

Re: Acer AL1914 Power Light on No Display

Pin 6 will read low resistance to ground because it is connected to the very low Ohm Source resistor of the MOSFET, not sure about pin 4 yet.

[selldoor]

Re: Acer AL1914 Power Light on No Display

Inverter transformer looks good- have you another panel or ccfl
so we can substitute for the current ccfls. Can you see the ends of the ccfls and wiring to see if they are black or burnt.

[budm]

Re: Acer AL1914 Power Light on No Display

Try using test lamp.
https://www.badcaps.net/forum/showthread.php?t=19987

[ZappedAgain]

Re: Acer AL1914 Power Light on No Display

I happened to have a working Acer AL1912 Monitor. Opened it up and the power supply is identical to the AL1914. Swapped the power supply out with the one from the AL1914 and the monitor works like a charm.

Looking at the bad LCD panel I can't see the CCFL's they look like they may be buried very well. Is there a guide for replacing the CCFL's? Haven't done a replacement of one of these yet. Anything else I should check first?

Thanks for the help so Far.