Can't seem to open Acer AL2416W case

[Mike_S456]

Re: Can't seem to open Acer AL2416W case

Yes...you are correct...it was a bad assumption on my part....thanks for pointing that out

[Toasty]

Re: Can't seem to open Acer AL2416W case

Elecktrotanya site SUCKS Locked out AGAIN!
If somebody gets this manual, would you send it to my Yahoo email as an attachment? TIA

Follow PlainBill on this. Has these diagnosis down cold.

Uses long tubes U-shaped 530mm tubes. Check test points from Service Manual. One wrong voltage compared to others will point at bad tube or involved circuit. Tubes are very susceptible to cracking either from factory, tube manufacture, or unit was dropped sometime.

Soldering on inverter caps is factory, as you said. Not fixed by someone. No one recaps with those caps and gray caulk. Look at blue coils below. Same solder job.

FireFox java SUCKS. - Third time I've lost this posting.

Toast

[ Don't be to concerned with the backside. To trace those from top to bottom you really need to have the card in your hands and a bright flashlight to track them. Doing it from pictures on the web is nigh impossible. A lot go top-bottom-top-under something-bottom-top... ]

[Mike_S456]

Re: Can't seem to open Acer AL2416W case

There seems to be six backlight tubes used....there are six output connectors on the board.......are you saying that if one is not working they all will not be working?...

[Toasty]

Re: Can't seem to open Acer AL2416W case

Correct. I've had 2 of these 24" units, both with cracked tubes. As soon as the inverter controller sees a voltage differential indicating over-voltage or over-current, it trips the unit to off. If you can keep hitting the power button over and over, and see the logo/desktop/whatever, then at least -some- of the tubes are working. As I said, PlainBill has more experience here.

Toast

[PlainBill]

Re: Can't seem to open Acer AL2416W case

Toasty is actually understating the case. An inverter is a constant-current high voltage source usually with over voltage and over current protection.

The circuitry usually senses the current through all CCFLs and adjusts the transformer drive to maintain the total design current through the CCFLs. (If a monitor has 4 CCFLs rated at 5mA each it will maintain 20 mA total current through the CCFLs.

Over voltage protection (OVP) shuts down the inverter if the voltage across any CCFL exceeds limits. Since current through a CCFL rises at end of life, Over current protection (OCP) shuts down the inverter if the current through any CCFL rises too high.

Essentially any anomaly will cause the inverter to shut down. Usually there is a 2 second delay from turn-on until it starts OVP and OCP is enabled.

I've marked up one of the photographs.

First step. I've numbered the pins on one of the transformers from 1 to 7. 1 is on the lower left corner, 6 is on the upper right, and is the output. Set your DMM on the 2K ohm scale and measure resistances from pin 6 to the other 5 pins (don't bother with pin 2). You should get a reading in the 1K range from pin 6 to only one other pin. This is the secondary winding. Now measure the resistance on the other 11 transformers. All should match to within 3%. If you find one that is outside this range, stop.

Next step. This test involves working with potentially lethal voltages. I suggest having an assistant. Note that I have labeled the lower end of C115 as Vsens. Hook up the boards in the normal working layout. Arrange it so your assistant can push the power button. Set the DMM to the 20VAC range. Now, probing from the bottom end of C115 to ground, try to get a voltage reading while the backlights are on. Repeat for C102, C137, etc.

Report your results.

Darn!! Can't find a datasheet for OZ9925GN.


PlainBill

[Toasty]

Re: Can't seem to open Acer AL2416W case

Browsing around I find that the 10 - 100uF/35v caps are suspects also, and since you are here, should be replaced as a matter of course.

I'd go with 50v caps in either Panasonic FM or UCC KZE series.

Mentioned also was checking the Q3-Q5 & Q4-Q6 MOSFETs. These can be compared to each other as Q3-4 are the same number, as are Q5-6.

[Mike_S456]

Re: Can't seem to open Acer AL2416W case

Ok..I have completed the first step. I numbered the transformers T1 to T12, 1 being on the far left and 12 being the far right. I made and attached a pdf file of the resistance values I measured.

I will have to wait until later for the second step to have someone available to help.

When measuring the voltage, where is the best ground on the board? I was thinking of using pins 6, 7. 8 .9 or 10 on the input connector

[Th3_uN1Qu3]

Re: Can't seem to open Acer AL2416W case

When measuring the voltage, where is the best ground on the board?

Wherever you see a plated screw hole.

[Mike_S456]

Re: Can't seem to open Acer AL2416W case

The 3 plated screw holes at the bottom of the board seem to be common to the ground plane (at least they are common to pins 6-10 on the input connector) but not the 3 screw holes at the top of the board

[Toasty]

Re: Can't seem to open Acer AL2416W case

Correct, the top three are not ground.

[PlainBill]

Re: Can't seem to open Acer AL2416W case

Ok..I have completed the first step. I numbered the transformers T1 to T12, 1 being on the far left and 12 being the far right. I made and attached a pdf file of the resistance values I measured.

I will have to wait until later for the second step to have someone available to help.

When measuring the voltage, where is the best ground on the board? I was thinking of using pins 6, 7. 8 .9 or 10 on the input connector

The transformers appear to be good. There is a 2% difference between the high and the low.

A proper ground point has been discussed.

And I have one more test. With the DMM on the 20VAC range, measure the voltage on pin 1 of each transformer while the CCFLs are on. This is the current sense line.

PlainBill

[dt2rz]

Re: Can't seem to open Acer AL2416W case

Toasty is actually understating the case. An inverter is a constant-current high voltage source usually with over voltage and over current protection.

The circuitry usually senses the current through all CCFLs and adjusts the transformer drive to maintain the total design current through the CCFLs. (If a monitor has 4 CCFLs rated at 5mA each it will maintain 20 mA total current through the CCFLs.

Over voltage protection (OVP) shuts down the inverter if the voltage across any CCFL exceeds limits. Since current through a CCFL rises at end of life, Over current protection (OCP) shuts down the inverter if the current through any CCFL rises too high.

Essentially any anomaly will cause the inverter to shut down. Usually there is a 2 second delay from turn-on until it starts OVP and OCP is enabled.

I've marked up one of the photographs.

First step. I've numbered the pins on one of the transformers from 1 to 7. 1 is on the lower left corner, 6 is on the upper right, and is the output. Set your DMM on the 2K ohm scale and measure resistances from pin 6 to the other 5 pins (don't bother with pin 2). You should get a reading in the 1K range from pin 6 to only one other pin. This is the secondary winding. Now measure the resistance on the other 11 transformers. All should match to within 3%. If you find one that is outside this range, stop.

Next step. This test involves working with potentially lethal voltages. I suggest having an assistant. Note that I have labeled the lower end of C115 as Vsens. Hook up the boards in the normal working layout. Arrange it so your assistant can push the power button. Set the DMM to the 20VAC range. Now, probing from the bottom end of C115 to ground, try to get a voltage reading while the backlights are on. Repeat for C102, C137, etc.

Report your results.

Darn!! Can't find a datasheet for OZ9925GN.


PlainBill

I did the first step but have different results from Mike_S456. Does this mean all transformers are bad? Hope you can guide me what to do next?

[Toasty]

Re: Can't seem to open Acer AL2416W case

>>I did the first step but have different results from Mike_S456.<<

What scale was your meter set to?

[PlainBill]

Re: Can't seem to open Acer AL2416W case

I did the first step but have different results from Mike_S456. Does this mean all transformers are bad? Hope you can guide me what to do next?

Your variation is larger than what Mike_S456, but usually if you have a bad transformer one transformer will be distinctly lower than the others. I don't think that any are bad.

Note to others. There was a communications problem on the description of the test. I asked Mike_S456 to test all pins on the transformer because I did not know which pin was the other end of the secondary. In the future, all you have to measure is the resistance between pin a and pin 6.


The two tests I suggested above will check for open or aged CCFLs. Do them.

PlainBill

[dt2rz]

Re: Can't seem to open Acer AL2416W case

Thanks Plainbill. I will continue the test when i get somebody to assist me.

@Toasty - DMM on the 2K ohm scale

[Mike_S456]

Re: Can't seem to open Acer AL2416W case

Am I performing test 2 and 3 correctly?........at the capacitor I'm reading about .8 VAC when the Acer logo comes on and about .35 VAC at pin 1. Doesn't seem right to me so before I continue I'm asking you. Thanks

[Toasty]

Re: Can't seem to open Acer AL2416W case

Thanks Plainbill. I will continue the test when i get somebody to assist me.

@Toasty - DMM on the 2K ohm scale

Different meters, different responses.

With it set on 2kΩ -
A 999Ω resistor would read .999 (.999kΩ)
A 1,000Ω would read 1.000 (1.000kΩ).
So your first row basically matches Mike_S456's results.

Your meter may not go high enough on the 2kΩ scale to reach megohms, but instead may just show a 1. or the OL indication. If you change the meter to the range where it will read ~5 megohms, you'll probably match Mike_S456 on those other legs.

Toast

[Toasty]

Re: Can't seem to open Acer AL2416W case

...Note to others. There was a communications problem on the description of the test. I asked Mike_S456 to test all pins on the transformer because I did not know which pin was the other end of the secondary. In the future, all you have to measure is the resistance between pin a and pin 6...

Pin a ?

[PlainBill]

Re: Can't seem to open Acer AL2416W case

Pin a ?

Typo. The secondary runs from pin 1 (not a) to pin 6.

PlainBill

[PlainBill]

Re: Can't seem to open Acer AL2416W case

Am I performing test 2 and 3 correctly?........at the capacitor I'm reading about .8 VAC when the Acer logo comes on and about .35 VAC at pin 1. Doesn't seem right to me so before I continue I'm asking you. Thanks

That could be right. Don't be afraid to drop to a lower range. I don't have more that a rough guess as to what the voltages should be. What we are looking for is a difference on the transformers that drive one CCFL. In other words, if 10 of the 12 transformers show .5 - .7 volts on pin 1, but two adjacent ones show .1 volts, that is significant. If 10 of 12 caps measure .8 - 1.3 volts, but the two associated with the same transformers that had a low voltage at pin 1 show 3 - 3.5 volts, that is a positive sign something is wrong with the CCFL connected to those transformers.

PlainBill