Viewsonic VX910

[PlainBill]

Re: Viewsonic VX910

I pulled the transformer, because with all this tinkering, and the fact I have a desoldering tool helps, its becoming easier to start pulling parts... I think this may be a problem. I attached a picture of it, and I'm not getting ohms readings and barely any continuity between pins. If looking at the picture, lets call the top 4 pins T1-T4 then Bottom 6 B1-B6. To simplify, I only get ohms readings between pins T2 and T4 429 ohms, B1 and B6 .2ohms B2 and B4 .2ohms B3 and B5 .2 ohms. Continuity tests agree with those pairs. Nothing else connects... Sound good or bad? I can't find a data sheet other than dimensions anywhere. On the parts list it says X'FMR, EPC-19H (12P), D=0.05, 1700Ts, FSP035-1PI01, 150mH Anyone want to decode that please? I know its a transformer, and the model is EPC-19 H Beyond that... It is also 10 pin. The letters on the side of it are
SPI STJ00029
0505 1 FC

The continuity readings would be normal. Remember, this is a Royer oscillator. Look at Figure 2 in this application note.

PlainBill

[ajsemtb]

Re: Viewsonic VX910

I pulled the transformer, because with all this tinkering, and the fact I have a desoldering tool helps, its becoming easier to start pulling parts... I think this may be a problem. I attached a picture of it, and I'm not getting ohms readings and barely any continuity between pins. If looking at the picture, lets call the top 4 pins T1-T4 then Bottom 6 B1-B6. To simplify, I only get ohms readings between pins T2 and T4 429 ohms, B1 and B6 .2ohms B2 and B4 .2ohms B3 and B5 .2 ohms. Continuity tests agree with those pairs. Nothing else connects... Sound good or bad? I can't find a data sheet other than dimensions anywhere. On the parts list it says X'FMR, EPC-19H (12P), D=0.05, 1700Ts, FSP035-1PI01, 150mH Anyone want to decode that please? I know its a transformer, and the model is EPC-19 H Beyond that... It is also 10 pin. The letters on the side of it are
SPI STJ00029
0505 1 FC

[retiredcaps]

Re: Viewsonic VX910

Sure, take the easy way out...

Actually, I don't have an exacto knife at home. Plus some of the older monitors I have fixed have hardened glue so it comes off pretty easily with just the fingers.

[ajsemtb]

Re: Viewsonic VX910

Sure, take the easy way out...

[retiredcaps]

Re: Viewsonic VX910

I have another question about that. I know you will probably want a picture but on the bottom there is some white glue substance over some of the pins. How do I remove it to remove the transformer if I Need to?

That glue was probably used during the assembly process to hold some component in place until it is finally soldered in.

I usually just use my fingers to pry apart the glue. Others use an exacto knife.

[ajsemtb]

Re: Viewsonic VX910

To test the transformers, you don't need any of those transistors installed.

You just need to measure the resistance (with power off and unplugged) of the legs of those EPC-19 transformers. Ideally, they should be measured out of circuit, but let's measure them in circuit once more. If the readings look funny, we can remove the transformer and remeasure out of circuit.

I have another question about that. I know you will probably want a picture but on the bottom there is some white glue substance over some of the pins. How do I remove it to remove the transformer if I Need to?

[retiredcaps]

Re: Viewsonic VX910

I can't perform that test right now because I have taken off the little transistors on the bottom to replace and I haven't reinstalled them yet.

To test the transformers, you don't need any of those transistors installed.

You just need to measure the resistance (with power off and unplugged) of the legs of those EPC-19 transformers. Ideally, they should be measured out of circuit, but let's measure them in circuit once more. If the readings look funny, we can remove the transformer and remeasure out of circuit.

[ajsemtb]

Re: Viewsonic VX910

Here are some good pics. (hint taken) Now keep in mind that this board has been recapped before with blue Xicon's and there is no way to know how much of the burn marks (dark areas) are from previous repairs and my repairs. In this pic, all the aluminum caps have been replaced with Panasonics (including the start up cap now) except for the big Kahuna. I have enough ceramic caps on order to replace the 2 little blue ones right by the littler transformers as well as the poly cap thats red on the other side of the transformer.

I can't perform that test right now because I have taken off the little transistors on the bottom to replace and I haven't reinstalled them yet. However, after removing them and testing them via ohm and diode test, it actually tested good, but I destroyed the other on removing it (they are tiny little suckers...). So I may not have popped them as I had thought before. No way to know now... OH I just remembered I actually did that test again, and no I don't have the exact number but it was around 55 ohms before I removed the transitors.

I'll do the test again once I have them back in place. Also, I should have the rest of my parts tomorrow for the other repairs.

Also, I tested the resistors in R18 and R22 and they are in tolerance to about 10%.

And also in these pics, the MOSFET is out. you say it sounds like its working?

[retiredcaps]

Re: Viewsonic VX910

Retired, I did that test on the transformer still installed, the best I could, and the one transformer T2 tests with 745 ohms, which I've read somewhere is supposed to be right. This one is testing 55.9 ohms.

Okay, let's run this test again as per post #36 and post the actual results of all your readings. I would like to see the actual pin to pin readings (the raw data) with the exact ohms reading for each one.

Just so we are clear, we are testing the two transformers in the upper corners near the connectors to the CCFL. I can't make out the designation because we don't have a decent picture (hint).

[retiredcaps]

Re: Viewsonic VX910

can I test capacitors with a DMM without capacitance test?

To test a cap properly, you need to test 2 things.

The uF itself. A multimeter with a capacitance check is required. For example, a 1000uF cap should measure roughly 1000uF. If it reads 88uF, it is obviously bad.

The second parameter to test is the ESR. A cap used in a SMPS environment should test around 0.3. An ESR tester is required to measure this.

[retiredcaps]

Re: Viewsonic VX910

Can anyone tell me if I have successfully tested this MOSFET?

Those results look okay.

[ajsemtb]

Re: Viewsonic VX910

Oh, and the other question was, can I test capacitors with a DMM without capacitance test? There was no ohm readings, continuity, or voltage (with diode test) on their respective function on the meter...

[ajsemtb]

Re: Viewsonic VX910

Ok, just to update, I resoldered the pins to the transformer that is on the failing side of the inverter board. I believe 1 side works, and the other doesn't because of values I've found on other threads match up. I desoldered 1 leg of each resistor that has heat shrink tube around it to test its value, and they are both in tolerance, (which was disappointing because the really big Cap was holding voltage for like 10 minutes and I read on another thread about that happening and a resistor being faulted and that solving that problem... )

I have also desoldered the MOSFET to test. When my DMM probes are not touching in OHM mode, it reads (blinking) 1 (not blinking)0.00M ohm. Closed (probes touching) it reads .1 ohms. With the continuity tester it has a blinking 1 followed by .000K when open, .001k OHMs when closed. And on diode mode 1.470 V open and 000 V closed. Just point of reference for the following tests.

ohms:
1-2 Blinking 10.00M
1-3 blinking 10.00M
2-3 17.68m counting down

1-2 no continuity
1-3 "
2-3 "
Diode
1-2 1.470
1-3 1.469
2-3 .489V

Can anyone tell me if I have successfully tested this MOSFET? I don't know if I even tested it right or not, and if I did what the results mean. Also, I tested with the black probe on the left, then went back with black on right, and that way they all failed...

[ajsemtb]

Re: Viewsonic VX910

OK, quick question. Should I be using Lead or Silver or lead free solder? I had another question, but it escapes me.. Sorry if I post again a short question in a few minutes...

[jetadm123]

Re: Viewsonic VX910

I'm trying to find the part number on Digikey for the C24 poly cap. In the service manual there are 2 optional parts: 1) cap, polyproplene, 154, J, 250V, 13L*6.5T*12H*10F,,MPP-154J0250DB110, HJC and 2) cap. polyester, 0.15uF, K, 160V, 13L*4T*9H*10F, BOX, R75GF3150, ARCO Can someone please let me know what the correct part is, because one is 250V the other is 160V is that AC or DC why is 1 154 and the other .15uF. ??? !!! I think its part number 495-1201-ND at Digikey, but it doesn't look like this part. thanks, I want to order parts tomorrow. ordering these, the resistor located in R320 and R112, and the ceramic caps at C26, C27.

Hopefully, this makes sense. 154 and .15uf are the same. The "154" is capacitor code for:

15 is the cap value followed by the multiplier (in this case 4 zeros) and the value is in pf. Therefore, we have:

150,000pf = 150nf = .15uf

J and K are the tolerances: +/- 5% and +/- 10%

Not sure why there's a difference in voltages of 250 vs 160

[ajsemtb]

Re: Viewsonic VX910

I'm trying to find the part number on Digikey for the C24 poly cap. In the service manual there are 2 optional parts: 1) cap, polyproplene, 154, J, 250V, 13L*6.5T*12H*10F,,MPP-154J0250DB110, HJC and 2) cap. polyester, 0.15uF, K, 160V, 13L*4T*9H*10F, BOX, R75GF3150, ARCO Can someone please let me know what the correct part is, because one is 250V the other is 160V is that AC or DC why is 1 154 and the other .15uF. ??? !!! I think its part number 495-1201-ND at Digikey, but it doesn't look like this part. thanks, I want to order parts tomorrow. ordering these, the resistor located in R320 and R112, and the ceramic caps at C26, C27.

[retiredcaps]

Re: Viewsonic VX910

Do I need to start taking this thing apart piece by piece and testing them all out of the board?

Maybe this video will help "Testing for Faulty Inverter Transformers Tutorial"

http://www.youtube.com/watch?v=eNuGWBPRGKA

[ajsemtb]

Re: Viewsonic VX910

Retired, I did that test on the transformer still installed, the best I could, and the one transformer T2 tests with 745 ohms, which I've read somewhere is supposed to be right. This one is testing 55.9 ohms. But thats across the whole "part" of this cluster. If I test the ohms of the transistors I replaced, its the same, if I put my tester in points R22 and R18 it get the same, so I'm not sure the transformer is bad per se... Do I need to start taking this thing apart piece by piece and testing them all out of the board?

[retiredcaps]

Re: Viewsonic VX910

Is there any chance that the transformer is dead? Are those replacable easy or cost effective?

The transformer converts the low voltage into high voltage to drive the ccfls. These can be bad. You can test for open windings on the transformer by (with power off and unplugged)

a) Number the pins on the transformers anyway you like
b) black probe on pin 1, red on pin 2 - record ohm
c) black probe on pin 1, red on pin 3 - record ohm
d) black probe on pin 1, red on pin 4 - record ohm
e) etc
f) black probe on pin 1, red on pin last - record ohm
g) black probe on pin 2, red on pin 3 - record ohm
h) black probe on pin 2, red on pin 4 - record ohm
i) etc
j) black probe on pin 2, red on pin last - record ohm
k) black probe on pin 3, red on pin 4 - record ohm
l) etc
m) finally, black probe on pin last-1, red on pin last - record ohm

I'm guessing the secondaries should read 950 ohm (this will vary for different transformers). The primaries should read 1.3 ohm. Some will be 0L. If one secondary is 950ohm and the other is 750ohm, that would indicate a problem.

This test is not exhaustive as it does not detect all faults. For that, you will need a ring tester to test the coils.

[ajsemtb]

Re: Viewsonic VX910

Quote from ajsemtb: I think someone said to change out the 2 ceramic capacitors... What are those and what do they look like? Also, what is the white "square" thingy on the top of the board that has a matching one on the other side?

If you're talking about the "square" units wrapped in yellow tape, those are the inverter transformers, which generate the high voltages required to light the backlights.

As for the two capacitors: I think what the person is talking about are the brown (or dark orange) caps directly below each inverter transformer. From memory, I think they are polypropolene caps stamped "154" and rated at 250volts. These caps have a tendency to fail and might be the cause of your problem.

Ok, well I'll order those, and I guess I'll bite the $2 bullet and buy the big capacitor also LOL and before replacing the transistors again. Is there any chance that the transformer is dead? Are those replacable easy or cost effective? Thanks again for all the tips.