DAC-19M009 dead?

[PlainBill]

Re: DAC-19M009 dead?

It could be a false "in circuit" reading. D110 is right next to R132 which is a 15 ohm resistor.

I would wait for PlainBill to see what he thinks. This is one area where I'm still learning and don't have hands on experience yet.

That is in the drive circuit to the gate of the FET. Yes, a 15 ohm resistor would certainly distort the diode test reading.

I'm at a serious disadvantage here, and am going to have to review the entire thread, but something strange is going on. OK, check that; something strange IS going on, but I'm convinced the TEA1532A is fine.

The fact that the voltage at pin 1 rises when the signal card is attached indicates there are drive pulses to the transformer. Now, what is going wrong? Maybe after I wake up....

PlainBill

[papagoose]

Re: DAC-19M009 dead?

Not sure if it would make a difference, but I didn't check the voltage with everything hooked up (I need to have the logic board upside down which made it difficult to connect the ribbon wires, wanted to avoid twisting them)- so of course I wasn't able to see if the LED still flashed once.

Also, thanks everyone for all the time you guys are putting in to helping me with this problem. I'm really blown away by how helpful everyone is here!

[PlainBill]

Re: DAC-19M009 dead?

[QUOTE=papagoose;169941<SNIP>

Also, thanks everyone for all the time you guys are putting in to helping me with this problem. I'm really blown away by how helpful everyone is here![/QUOTE]

It's all a matter of getting the satisfaction of accomplishing something. Some people get their satisfaction out of becoming a CEO, President, or Prime Minister. We get our jollies by doing something more important (and difficult) - helping people fix monitors and TVs.

PlainBill

[papagoose]

Re: DAC-19M009 dead?

Bump- weekend is coming up, any ideas on what to test next?

[PlainBill]

Re: DAC-19M009 dead?

Bump- weekend is coming up, any ideas on what to test next?

OK, but remember, you asked!!!

I've uploaded a picture after marking up a few points of interest.

1. Black circle in lower left corner - use this as the ground point.

Initial steps are with power off

2. Yellow circle near lower left corner - what is the part number of that IC? I don't think it's the cause of the problem, I just want to know what it is.

3. Diode circled in beige. Check it for shorts - you can do this in circuit.

The next steps are done with the signal (logic) board unplugged from the power supply, and the power supply connected to the AC mains.

4. Red circle. What is the voltage?

5. Blue circle. What is the voltage?

Disconnect the power supply from the AC mains, wait at least 10 minutes, then plug the power supply into the signal board. The signal board can be disconnected from the LCD panel and the front panel. Now connect the power supply to the AC mains.

6. Red circle. What is the voltage?

7. Blue circle. What is the voltage?

There is something odd going on. Usually we see only one photo-coupler. This supply has two.

PlainBill

[papagoose]

Re: DAC-19M009 dead?

2. Yellow circle near lower left corner - what is the part number of that IC? I don't think it's the cause of the problem, I just want to know what it is.

LM393

3. Diode circled in beige. Check it for shorts - you can do this in circuit.

With the black probe on the top (same orientation as in the image) the multimeter reads 800. In the other direction, it reads about 2000

The next steps are done with the signal (logic) board unplugged from the power supply, and the power supply connected to the AC mains.

4. Red circle. What is the voltage?

5. Blue circle. What is the voltage?

Red = 5V
Blue = 0V

Disconnect the power supply from the AC mains, wait at least 10 minutes, then plug the power supply into the signal board. The signal board can be disconnected from the LCD panel and the front panel. Now connect the power supply to the AC mains.

6. Red circle. What is the voltage?

7. Blue circle. What is the voltage?

The same as before, Red=5V Blue = 0V

[PlainBill]

Re: DAC-19M009 dead?

LM393


With the black probe on the top (same orientation as in the image) the multimeter reads 800. In the other direction, it reads about 2000



Red = 5V
Blue = 0V


The same as before, Red=5V Blue = 0V

Well!! We are making some kind of progress.

Once again, I'm resorting to Paint. The only good part of Paint is no clean-up is required.

Your mission, should you decide to accept it, is to perform some rudimentary tests on the transformer. Do this with power off, please.

Note that I have circled one point in black, and numbered the pins of the transformer from 1-6. With the DMM set to the 200 ohm range, measure the resistance between the point circled in black and each of the numbered pins. Try to measure to the tip of the pin, not to the surrounding solder or the trace itself. Then repeat this, but measuring to the traces, not the tip of the pin.

I would expect all resistances to be under 1 ohm.

PlainBill

[papagoose]

Re: DAC-19M009 dead?

I've measured it carefully touching the tips of the pins, all of them read <1 ohm. I'm not sure what to measure for the traces- are these the metal strips nearby?

The photo makes it painfully clear where I've slightly burned the board resoldering it! :p (other posts mentioned resoldering the transformer, I tried that before I started this thread)

[PlainBill]

Re: DAC-19M009 dead?

I've measured it carefully touching the tips of the pins, all of them read <1 ohm. I'm not sure what to measure for the traces- are these the metal strips nearby?

The photo makes it painfully clear where I've slightly burned the board resoldering it! :p (other posts mentioned resoldering the transformer, I tried that before I started this thread)

Oh, petals!! Well, ours is not to do or die, ours is but to reason why. The good news is that indicates the transformer is good.

The traces are the metal strips leading from the posts to the leads for the diodes. Lead free solder is notorious for producing joints that look good, but are faulty. So let's do the second part of the assignment. Measure the resistance from the spot circled in black to point 7 (the solder), and to points 8 and 9 (the tips of the pins.

Next step. Set your DMM to the 20 VAC range. Yes, I want you to try to measure AC!! With the monitor connected to AC power, measure the voltage from the point circled in black to point 7 and also to point 10. If either reads out of range, step up to the 200 VAC range.

PlainBill

[papagoose]

Re: DAC-19M009 dead?

This may be a silly question, but I can't see 7-10 in the previous photo? Should I be looking near the transformer as before? Or is there a missing attachment?

[PlainBill]

Re: DAC-19M009 dead?

This may be a silly question, but I can't see 7-10 in the previous photo? Should I be looking near the transformer as before? Or is there a missing attachment?

Oops!!! I used invisible paint!!

PlainBill

[papagoose]

Re: DAC-19M009 dead?

I've measured all the resistances, they are less than 1 ohm. My multimeter only has 750V and 250V in AC mode. When I measure the voltages from the black circle to 7 and 10, they are both essentially zero (it flucuated around 0.02 and -0.02). This is with the logic board disconnected. I checked the pins that go to the logic board, and they were showing the usual 5V etc.

Also, while I remember, the glass fuse F200 on the top of the board is still disconnected from testing before. Should I put it back now?

[PlainBill]

Re: DAC-19M009 dead?

I've measured all the resistances, they are less than 1 ohm. My multimeter only has 750V and 250V in AC mode. When I measure the voltages from the black circle to 7 and 10, they are both essentially zero (it flucuated around 0.02 and -0.02). This is with the logic board disconnected. I checked the pins that go to the logic board, and they were showing the usual 5V etc.

That was somewhat of a long shot. I guess the DMM doesn't have the frequency response to read a 70 Khz signal.

Also, while I remember, the glass fuse F200 on the top of the board is still disconnected from testing before. Should I put it back now?

No, leave that disconnected for now. I'm trying to establish why you don't get 12V out of the power supply. The fewer complications, the better.

Let's try something original here. I'm trying to run down the schematic for the power supply with very limited success, keep track of a baseball game, and keep track of the time because I have to pick up some family from the airport.

Test 1. Power disconnected. DMM on the 200 ohm scale. Black lead on the black circle. Measure the resistance to the lead between 8 and 9 on the latest picture. This should read open.

Test 2. Now switch to the diode check scale and measure with the leads on the same points. What is the reading?

Test 3. Reverse the leads - Red to the black circle, black to the point between 8 and 9. What is the reading?

PlainBill

[papagoose]

Re: DAC-19M009 dead?

Test 1. Power disconnected. DMM on the 200 ohm scale. Black lead on the black circle. Measure the resistance to the lead between 8 and 9 on the latest picture. This should read open.

The resistance is < 1 ohm

Test 2. Now switch to the diode check scale and measure with the leads on the same points. What is the reading?

The diode test read 0

Test 3. Reverse the leads - Red to the black circle, black to the point between 8 and 9. What is the reading?

And this read 0 as well!

[PlainBill]

Re: DAC-19M009 dead?

The resistance is < 1 ohm


The diode test read 0


And this read 0 as well!

Charming. Refer to the attached picture. If you would, remove the diode circled in red. Then measure the resistance between the two points circled in black. Also test the diode by setting the meter in diode test range and checking from the center lead to each side lead. Then reverse the DMM leads and test again.

PlainBill

[papagoose]

Re: DAC-19M009 dead?

Haha it would have to be one of the diodes that is screwed into one of the metal dividers on the other side of the board! Just waiting for the soldering iron to heat up now...

[papagoose]

Re: DAC-19M009 dead?

Charming. Refer to the attached picture. If you would, remove the diode circled in red. Then measure the resistance between the two points circled in black. Also test the diode by setting the meter in diode test range and checking from the center lead to each side lead. Then reverse the DMM leads and test again.

PlainBill

OK now I am excited! With the diode out, the resistance between the two circled points is off scale (they don't seem to be connected).

Am I correct in thinking this diode is actually 2 diodes put together? If I understand the drawing on the front correctly, they are connected in opposite directions. One of them reads 350 one way and off scale the other. The other reads 0 in both directions

[retiredcaps]

Re: DAC-19M009 dead?

Am I correct in thinking this diode is actually 2 diodes put together? If I understand the drawing on the front correctly, they are connected in opposite directions. One of them reads 350 one way and off scale the other. The other reads 0 in both directions

If it looks like this

http://en.wikipedia.org/wiki/File:Schottky.jpg

then the 0 reading suggests it is a bad component.

[papagoose]

Re: DAC-19M009 dead?

If it looks like this

http://en.wikipedia.org/wiki/File:Schottky.jpg

then the 0 reading suggests it is a bad component.

Yep it looks like those, same symbol drawn on them. So it sounds like we know what to replace next...?

[retiredcaps]

Re: DAC-19M009 dead?

What is the part number on that diode?