emachines e19t6w inverter powersupply help

[jselvatici]

Re: emachines e19t6w inverter powersupply help

PS. I tested this on a working LCD. If I put my black on a ground screw on the secondary side and red on the middle pin of my dual diode, I get 5V DC.

Looking at page 69 of the schematics (vx1945wm-3.pdf), pins 8 and 9 go right into D805. You should get 5V DC. If not, either the diode is bad or the transformer isn't working.

You can double check the dual diode by using the diode check on your multimeter. Test it like any normal diode. I believe the middle pin is your negative.

Okay,

D805 there's no 5V DC on it. and the transformer is not provinding any voltage. D803 has the same behavior.

I did the diode check on both and the results are:
D805 -> Between 1 and 2 = 0,150 ohm and is the same for 3 and 2.
also, if you go in the reverse way, the multimeter is giving me 1.520 ohms. Is not suppose to not conduct in this way? or is this type of diode?

D803 -> Between 1 and 2 = 0,300 ohm and is the same for 3 and 2.
Nothing on reverse way with multimeter in diode test scale.

So, we have to move before these diodes right? The transformer? or before it?

What about AP2761? (Q804) It was shorted in the very beggining and I replace it by K2843 (because in the components store, they told me that was compatible, is not?)

Tks.

[retiredcaps]

Re: emachines e19t6w inverter powersupply help

I did the diode check on both and the results are:
D805 -> Between 1 and 2 = 0,150 ohm and is the same for 3 and 2.
also, if you go in the reverse way, the multimeter is giving me 1.520 ohms. Is not suppose to not conduct in this way? or is this type of diode?

D803 -> Between 1 and 2 = 0,300 ohm and is the same for 3 and 2.
Nothing on reverse way with multimeter in diode test scale.

I think those readings look correct.

So, we have to move before these diodes right? The transformer? or before it?

From the schematics, pin 8 and 9 go right into D805. There is nothing else "before" it. And you get 308V DC on pin 1 and 3 (which is correct).

I believe this provides more evidence that the transformer is not working properly on the secondary side.

[jselvatici]

Re: emachines e19t6w inverter powersupply help

I believe this provides more evidence that the transformer is not working properly on the secondary side.

I have the same clue... But I was checking for the transformer, and this SPW-055 is not so easy to find.

Here where I live, will be much harder..

Something else to check before goes to transformer replacement?

Tks!

[retiredcaps]

Re: emachines e19t6w inverter powersupply help

Something else to check before goes to transformer replacement?

I would suspect the SMPS controller (NCP1337), but you have already replaced it twice (once from initial damage and again after voltage testing/short).

The only other thing I can think of is IC801, the optoisolater. It provides feedback from the secondary side back to the primary side. Pin 2 goes right into NCP1337.

Test Pin 1 and 2 like a diode. Pin 3 and 4 should have 0.3 ohms resistance. Resitance between 1 to 4 and 2 to 3 should read inifinite ohms.

[retiredcaps]

Re: emachines e19t6w inverter powersupply help

Also, on pin 4 of the transformer, it goes to D804. From D804, it goes on pin 6 of NCP1337. Last time, you measured pin 6 it was 0V DC. This didn't look right to me initially.

So retest diode D804 with the diode test and make sure it works. Then measure the voltage on D804.

Again, I'm using page 69 schematic for reference.

[pedro]

Re: emachines e19t6w inverter powersupply help

The only other thing I can think of is IC801, the optoisolater. It provides feedback from the secondary side back to the primary side. Pin 2 goes right into NCP1337.

Test Pin 1 and 2 like a diode. Pin 3 and 4 should have 0.3 ohms resistance. Resitance between 1 to 4 and 2 to 3 should read inifinite ohms.

??? Without going off chasing the opto's details, if 1 & 2 are the LED (most common in 4-pin DIP optos) and 3,4 are the transistor then 3,4 should certainly NOT measure 0.3 ohms. It should be a very high reading both ways.

[retiredcaps]

Re: emachines e19t6w inverter powersupply help

??? Without going off chasing the opto's details, if 1 & 2 are the LED (most common in 4-pin DIP optos) and 3,4 are the transistor then 3,4 should certainly NOT measure 0.3 ohms. It should be a very high reading both ways.

Good catch. I meant NOT 0.3 ohms. It's hard flipping back and forth on one monitor!

Also, I made a typo on the pin going to the NCP1337. It is pin 3 of the opto that goes pin 2 of the NCP1337.

[jetadm123]

Re: emachines e19t6w inverter powersupply help

No luck my friend...

I change the FET, Resistor, the Fuse and the 47uF Cap and no 5VDC in the output...

Any new idea?

When you changed R805 what value did you use? The schematic says 0.18 ohms at 2 Watts. I'm asking because initially looking at the photo of the resistor I thought it was 18 ohms.

[jselvatici]

Re: emachines e19t6w inverter powersupply help

When you changed R805 what value did you use? The schematic says 0.18 ohms at 2 Watts. I'm asking because initially looking at the photo of the resistor I thought it was 18 ohms.

Well, now I have 0.24 ohms resistor (Is exactly the same as the original that was installed before).

Facing this resistor, my board don't look like the one in the file vg1930wm-1_sm.pdf ?? (Page 62)

tks.

[jetadm123]

Re: emachines e19t6w inverter powersupply help

Well, now I have 0.24 ohms resistor (Is exactly the same as the original that was installed before).

Facing this resistor, my board don't look like the one in the file vg1930wm-1_sm.pdf ?? (Page 62)

tks.

Just a minute.... In post #55 you show a photo of the original R805, which according to it's color code is .18 ohms. Now your saying the original was .24 ohms?

[jselvatici]

Re: emachines e19t6w inverter powersupply help

Just a minute.... In post #55 you show a photo of the original R805, which according to it's color code is .18 ohms. Now your saying the original was .24 ohms?

Yeap.

Because in the very beggining I have just that on hands...

After that blows up, I bought the exactly one that the board has...

Do you think that are problems with this difference?

many tks!

[drdbrown]

Re: emachines e19t6w inverter powersupply help

I fixed this “shutdown after a few seconds” problem on a Viewsonic VA1930 by replacing the electrolytic caps on the power board and re-soldering the power transformer joints (SPW-055). A startup buzzy noise was coming from the transformer, and I found that if it was torqued slightly the noise would stop leading me to the cold solder joints which must have been caused due to their large posts that were not heated up enough during construction. Who knows, perhaps the bad joint’s extra resistance caused a cap to overheat (the large, 1000mf one was swollen and leaking) because after replacing them the squealing was stronger and allowed a longer running time to locate the cold joint.

BTW: The transformer still has a 1 second squeal when first powered up then all is quiet as the backlights are working. I know most of these circuits have a high voltage startup surge to light up the CFLs which then drops after a second to running voltage, the circuitry then tests the voltages to see if they are nominal and shuts down if they are wrong. I wonder if anyone out there with this board has noticed the same one second startup squeal. If not, I might have a bad winding and my fix is temporary. Anyone?
David
(ps. Thanks for all the hints in this thread!!!)