DAC-19M009 dead?

[papagoose]

Hi all,

I have a Chimei 22" monitor with a problematic Delta DAC-19M009 inverter. When I plug it in and turn on the power, after a couple of seconds the green power LED flashes once, and then nothing else happens. I opened it up and had a look at the caps, but they all seemed fine. I replaced them first with some general purpose caps I had (which didn't work) so I've changed all of them except the big one for Panasonic FC and FM caps. But this hasn't changed the problem. The rest of the system is fine, I tested it with a known good DAC-19M009 and it powered on OK (at least, it was when I started! Unless something else I did broke it in the meantime...)

There didn't appear to be anything else wrong with the board. There are some scorch marks in the photo of the back (near soldering points) but those weren't there originally (my clumsy soldering :P). When I turn it on, there is a high pitched squeal exactly as I would expect from it normally turning on, and then the green light turns on. But then the LED turns off, and nothing else happens, the CCFLs never light up. If I cycle the power at the wall, it doesn't do it again immediately (nothing happens), I have to wait a minute to start it all again.

Any ideas? I don't have much experience with electronics or working with mains power so I'm not really comfortable measuring the voltage across the big cap while it is powered on

[retiredcaps]

Re: DAC-19M009 dead?

I don't have much experience with electronics or working with mains power so I'm not really comfortable measuring the voltage across the big cap while it is powered on

1) Test fuse F200. A good fuse should measure less than 1.0 ohms.

2) Post a picture of the logic board.

3) What are the DC voltages on the connector pins between the power/inverter and logic board? Those secondary voltages should be 24V DC or less. Use a ground screw for your black probe.

4) Hookup a working computer with your favourite wallpaper to the lcd. If you shine a flashlight on it, can you see the wallpaper?

[seanc]

Re: DAC-19M009 dead?

I can see a little capacitor near the bottom of the PSU - have you changed this?

[papagoose]

Re: DAC-19M009 dead?

Thanks for the fast replies

1) Test fuse F200. A good fuse should measure less than 1.0 ohms.

I measured 0.5 ohms

2) Post a picture of the logic board.

(attached) But I think that the logic board is fine. I tested this again with the working DAC-19M009 and it worked perfectly

3) What are the DC voltages on the connector pins between the power/inverter and logic board? Those secondary voltages should be 24V DC or less. Use a ground screw for your black probe.

I measured everything as zero, except for 3 of them which were 13.4V, 5V and 5V. These pins are marked on the board as +13.8V, +5V and +5V

4) Hookup a working computer with your favourite wallpaper to the lcd. If you shine a flashlight on it, can you see the wallpaper?

Can't see anything, but that doesn't surprise me. I had a monitor before where the inverter was powering the logic board but not the backlight, and in this case the power LED on the front still lit up correctly. In my case, the LED blinks on once and then stays off

I can see a little capacitor near the bottom of the PSU - have you changed this?

The tiny brown one? I haven't done anything with that. The top seems flat

Also, is the board meant to make different sounds when it isn't plugged into anything? While I was testing the pins, I had only the power cord connected, I didn't plug in any of the CCFLs. I recorded this http://******/miVE9M (it was going the whole time I was testing) but I couldn't localize the sound. It doesn't do this when the logic board is connected.

[seanc]

Re: DAC-19M009 dead?

Doesn't matter if it looks OK, it's probably dead.
It's an important startup capacitor.
As for the sound, sounds like the PSU is trying to startup over and over.

[retiredcaps]

Re: DAC-19M009 dead?

so I've changed all of them except the big one for Panasonic FC and FM caps.

Like seanc says, the little cap plays an important role in the startup process. If bad, it is never usually bloated.

And when you say "all", you really have to mean all.

[papagoose]

Re: DAC-19M009 dead?

And when you say "all", you really have to mean all.

Hahha quite true, I'll find a replacement and give it a go. The other reason I hadn't replaced it is that the supplier I got the other caps from didn't have a 22uF 50V low ESR - if I can't find a low ESR one, is there anything else that would be better than general purpose?

[retiredcaps]

Re: DAC-19M009 dead?

I measured everything as zero, except for 3 of them which were 13.4V, 5V and 5V. These pins are marked on the board as +13.8V, +5V and +5V

That implies that the SMPS is working (including the startup cap).

Check the U202 and U203 mosfets to see if they are shorted or not. A few people report them as bad.

[sabre504]

Re: DAC-19M009 dead?

They should be AOP605 MOSFET

"F102" 4A SMD Fuse

[papagoose]

Re: DAC-19M009 dead?

That implies that the SMPS is working (including the startup cap).

Check the U202 and U203 mosfets to see if they are shorted or not. A few people report them as bad.

Sure, how should I go about checking them?

[retiredcaps]

Re: DAC-19M009 dead?

Sure, how should I go about checking them?

See

2) Shorted Transistors/MOSFETs

https://www.badcaps.net/forum/showpo...0&postcount=13

[papagoose]

Re: DAC-19M009 dead?

This may be a daft question, but I'm using the data sheet here Is the orientation of the MOSFET the same in the picture and in the pin diagram? That is, in the picture at the 'base' of the MOSFET is a cut-out semicircle, is this on the G1/D1 side of the MOSFET?

If that is the case, then S1-G1 is really low (like 0.1 ohm), but all the others are like 1000k (so the MOSFETs are shorted). The alternative is that the circle on the top of the MOSFET marks pin 1. If that is the case, then S-G is off scale, G-D is off scale, and S-D is around 1000k (so they seem OK, and the 0.1 ohms in the previous test was actually testing resistance between the two D1 and D2 pins, so being really low would make sense)

[retiredcaps]

Re: DAC-19M009 dead?

1) See attachment for pin numbering.

Any reading under 30 ohms suggest the mosfet is shorted and potentially bad.

2) Did you measure that smd fuse in post #9? Your photo is too blurry for me to know where it is.

[papagoose]

Re: DAC-19M009 dead?

1) See attachment for pin numbering.

Any reading under 30 ohms suggest the mosfet is shorted and potentially bad.

Thanks for the attachment, none of the readings are below 30 ohms

2) Did you measure that smd fuse in post #9? Your photo is too blurry for me to know where it is.

I spent ages looking for F104 before realising I'd misread the original post! I think F102 is fine, I measured 0.5 ohms. I've attached an update of the back showing where F102 is for future reference

[retiredcaps]

Re: DAC-19M009 dead?

When I plug it in and turn on the power, after a couple of seconds the green power LED flashes once, and then nothing else happens.

The rest of the system is fine, I tested it with a known good DAC-19M009 and it powered on OK (at least, it was when I started!

Let's try this. Hookup all the boards without the ccfls plugged in (disconnect all ccfls). Does the power LED stay on now?

[papagoose]

Re: DAC-19M009 dead?

Let's try this. Hookup all the boards without the ccfls plugged in (disconnect all ccfls). Does the power LED stay on now?

No luck. I have the inverter connected to the logic board and none of the CCFLs plugged in, but the light still flashes on once and then stays off. As with before, the board doesn't make the sound that I uploaded, it only does that when it is disconnected from everything else.

[retiredcaps]

Re: DAC-19M009 dead?

if I can't find a low ESR one, is there anything else that would be better than general purpose?

The start cap is usually "entry level" low ESR like a Panasonic FC. You should replace even though the secondary voltages (13.8V and 5V DC) are present.

[retiredcaps]

Re: DAC-19M009 dead?

I know your logic board is good, but I'm curious about the voltages on the 2 circled voltage regulators (red and yellow).

Put your black probe on the ground screw and red on each pin (not the tab). Report

a) part number of each
b) DC voltage of each pin

When measuring these DC voltages, is the power LED on or off? The logic board controls this power LED.

[papagoose]

Re: DAC-19M009 dead?

I know your logic board is good, but I'm curious about the voltages on the 2 circled voltage regulators (red and yellow).

Put your black probe on the ground screw and red on each pin (not the tab). Report

a) part number of each
b) DC voltage of each pin

When measuring these DC voltages, is the power LED on or off? The logic board controls this power LED.

Okay, so I've replaced the small 22uF cap and that hasn't changed anything either. I did check the voltage regulators but I found something more interesting afterwards

Both the regulators have written on them

EH16A
621J15

Now when I turn the power on, the middle regulator's lowest pin reads 5V, the big pin about 3.6V, and the others are I think zero. However, 3 seconds later the LED blinks on, and then everything drops to zero. That would probably explain the LED turning off. So I thought I should check the connector pins from the inverter board going into the logic board.

When disconnected, the top two pins read 13.6V and 5V respectively, and they did that as long as the power was on (from my previous measurement). Now, when I turn the power on, they read 14V and 5V. Pretty much exactly 3s later, there is a quiet clicking sound, and both of these drop to zero. The voltage drop is gradual, and I bet if I recorded it, the result would be something resembling an exponential (so it drops to say 1V very quickly, and then slows). The clicking sound just about coincides with the LED lighting up. So right after the LED flashes on, there is no power going into the logic board!

There is still an electrical buzz from the big cap area, it is there the whole time (even after the LED turns off)

[retiredcaps]

Re: DAC-19M009 dead?

There is still an electrical buzz from the big cap area, it is there the whole time (even after the LED turns off)

Okay, it sounds like the power supply is failing under load.

If you have aligator clips, use them to attach to the big cap to take DC voltage readings (since you are not comfortable with live voltages).

Clip the aligator leads (red to positive, black to negative). Turn on the lcd and watch the DC voltage. It should be around 160 to 165V DC. See if this voltage drops or fluctuates. Make sure to note the voltage in the first 3 seconds and afterwards.

Aligator clips allow you to take readings hands free can be purchased pretty much anywhere and look like