Viewsonic VX910

[retiredcaps]

Re: Viewsonic VX910

What are the fuses on this board? And to clarify, the transistors are are mounted to the heat sink?

Fuses are marked with the letter F. Some picofuses are PF. For example, F100 or PF701.

Transistors are marked with the letter Q. Transistors may be mounted to a heat sink.

Do caps get hot?

Caps can get hot. If they sit next to transistors and the heat flow is directed towards the caps, they will get hot and eventually die from heat and drying out.

[ajsemtb]

Re: Viewsonic VX910

I'm went and looked at digikey for the transistors, and theres 6 different ones in the listings... Simple question, 120@500mV,2A gain or 82@500mV,2A gain?

http://search.digikey.com/scripts/Dk...672+&x=20&y=13

[retiredcaps]

Re: Viewsonic VX910

Simple question, 120@500mV,2A gain or 82@500mV,2A gain?

Post a pic of the part that you are trying to replace. Posting pic guideline is at

https://www.badcaps.net/forum/showthread.php?t=1868

[momaka]

Re: Viewsonic VX910

Also, looking at this board a little closer, I'm thinking these caps have already been replaced once. Well, the Xicon ones anyway.

Xicon? Are they blue or light blue by any chance? If so, perhaps someone has recapped it indeed (with the wrong type of caps, that is). If I'm not mistaken, Radio Shack sells those Xicon caps - and they are definitely not suitable for monitor repair.

[ajsemtb]

Re: Viewsonic VX910

Xicon? Are they blue or light blue by any chance? If so, perhaps someone has recapped it indeed (with the wrong type of caps, that is). If I'm not mistaken, Radio Shack sells those Xicon caps - and they are definitely not suitable for monitor repair.

Yes they are blue and the 35v ones instead of the 25v ones I've been reading about.

And RetiredCaps, I don't have access to a camera right now, however, in the 5th posting of this thread are pics from PlainBill with the transistors boxed in Red. Those are the ones to which I'm referring. Also, I did a test on the transitors that are attached directly to the heat sink, and I'm not sure which leg is actually which, but number 1-2-3 from right to left when upside down I'm getting these ohm readings:

1-2 the number starts at 1k and starts climbing, and doesn't stop
1-3 .1ohms
2-3 is 4.7m and counting down...

Honestly, I have no idea what his means.. LOL

1-2 15.71m and counting down
1-3 9.05k
2-3 14.94k and counting down

Also, I found the fuse, it was heatshrinked in black but I'm getting a reading of .2 to .1 ohms on it as well.

https://www.badcaps.net/forum/attach...1&d=1280705628

https://www.badcaps.net/forum/attach...1&d=1280705635

[retiredcaps]

Re: Viewsonic VX910

1-2 the number starts at 1k and starts climbing, and doesn't stop
1-3 .1ohms
2-3 is 4.7m and counting down...

Also, I found the fuse, it was heatshrinked in black but I'm getting a reading of .2 to .1 ohms on it as well.

If pin1-3 on the transistor reads 0.1 ohms when it is out of circuit, it is definitely shorted (bad).

The fuse is okay at 0.1 or 0.2 ohms. Some multimeters have a lower resistance for their probes.

[RJARRRPCGP]

Re: Viewsonic VX910

I like the soldering videos by Curious Inventer on youtube.com.

+1

I finally didn't feel like I had to guess!

[ajsemtb]

Re: Viewsonic VX910

Ok, well I'm sorry again, but I didn't remove it from the circuit... I thought I could test these still installed to the board. :/ SO, this all being said, which caps do I need to buy, and when I type in the search engine at the digikey or mouser or whatever the other one was, there are 600 options that all say the same thing for different prices. What specifically should I buy for caps and the tiny transistors on the bottom of the board? What has been used in this installation before and has worked? The parts range from .29 to 2.89 which is a heck of a swing, and I would like to do this repair for less than buying a new power supply board.

Regarding the transistors mounted to the heat sinks, I'll remove them tomorrow and retest and post results.

Thanks again for all your help, I'm learning a lot as we go along.

Also, I have an Insignia 32 lcd model# NS-32LCD that has died. It too has a common problem with caps going bad on the power supply board, and again, mine aren't bulged. Which doesn't mean they aren't bad, but I honestly care more about getting my tv working again than this monitor at this exact moment only because I have 2 22" monitors another 19" and my laptop monitor making up my array, this particular monitor just went out, and I replaced it. BUT my TV not working sucks way more... LOL I have searched these threads, but don't see the Insignia come up, but I'm too new to start a new thread, and I don't want to hijack this thread, so I'm trying to use my experience from fixing the monitor before I tackle my TV.

[Krankshaft]

Re: Viewsonic VX910

Xicon? Are they blue or light blue by any chance? If so, perhaps someone has recapped it indeed (with the wrong type of caps, that is). If I'm not mistaken, Radio Shack sells those Xicon caps - and they are definitely not suitable for monitor repair.

Not only are they not suitable for monitor repair Xicon's light blue GP caps are 85C rated. Only their radioactive green GP caps are 105C rated and even those aren't suitable since they're GP.

Definitely a Radioshack special you've got there.

When measuring the transistors be sure to use the diode check function on the meter and not the resistance function. You're testing for voltage drop not resistance.

[retiredcaps]

Re: Viewsonic VX910

Ok, well I'm sorry again, but I didn't remove it from the circuit... I thought I could test these still installed to the board. :/ SO, this all being said, which caps do I need to buy, and when I type in the search engine at the digikey or mouser or whatever the other one was, there are 600 options that all say the same thing for different prices. What specifically should I buy for caps and the tiny transistors on the bottom of the board? What has been used in this installation before and has worked? The parts range from .29 to 2.89 which is a heck of a swing, and I would like to do this repair for less than buying a new power supply board.

You can test transistors in circuit, but sometimes depending on how they are laid out, the results may not be 100% accurate so you need to remove them and test them out of circuit.

You need to make a list of the uF V, height and diameter of each capacitor and then follow PlainBill's instructions at

https://www.badcaps.net/forum/showpo...33&postcount=2

There is no "standard" list because each board can be a different revision and have different cap values (hence the request for pictures). Panasonic FM or FC caps are good low ESR choices.

My board "looks like" someone else may be a false sense of security. It is always better to make sure by reading the values of the caps on your own board.

Once you compile a list, some members here can verify.

[ajsemtb]

Re: Viewsonic VX910

Ok, well I ordered new caps (all except the very big one...probably come back to bite me but...) new transistors that flush mount the bottom, and a couple diodes that were mentioned that go out. All in all $12 including shipping. I ordered panasonic mainly FM but the little one was an FC. I'll update and let you all know how the repair goes.

[ajsemtb]

Re: Viewsonic VX910

Update, it didn't work... I recapped the 4 "main" ones, the 470uFs and the 330uFs. I didn't replace the really big one or the tiny one right next to the big one. I replaced the tiny transitors on the bottom. There is a difference now, as the screen at least flickers ever 2 seconds when the light blinks now. That is new. I hear a clicking each time it tris to turn on though. I heard it before also, when the ps was on my bench I plugged it in and heard a clicking as it cycled through.

When I installed the transitors, I tested them compared to the pair that I think work, and they gave me the same readings. Well, after my test, I think they shorted again, because for voltage they were at .270 and now they are .023. So that sucks. Luckily I bought 4 to do all of them, but Im pretty sure its just the one side thats fried. SO, that being said, besides replacing the only 2 caps I didn't change yet, what else could I test? what would be clicking?

Also, after my bench test, the really big Cap is holding voltage. 12v and with my DMM on it it slowly goes down. Its been almost 10 minutes and I'm at 7v and counting... Any thoughts?

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?

Thanks again for all your help. I'm not giving up yet...

[retiredcaps]

Re: Viewsonic VX910

I didn't replace the really big one or the tiny one right next to the big one. I replaced the tiny transitors on the bottom. There is a difference now, as the screen at least flickers ever 2 seconds when the light blinks now. That is new. I hear a clicking each time it tris to turn on though.

When I installed the transitors, I tested them compared to the pair that I think work, and they gave me the same readings. Well, after my test, I think they shorted again, because for voltage they were at .270 and now they are .023. So that sucks.

The little cap is sometimes called a startup/run cap. It is usually in the 1uF/2uF 50V range or something like 22uF/50V. That cap doesn't have to bloat to be bad.

The clicking sound maybe the SMPS trying to startup. The little cap helps the SMPS startup.

Which leads to ... replace the little cap. That may solve the problem?

If the transistors are shorted again, resolder all the transformer pins (the 2 yellow things marked with T). Remove the old solder and resolder with fresh solder.

edit: Here is PlainBill talking about the startup cap ...

https://www.badcaps.net/forum/showpo...97&postcount=2

[jetadm123]

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.

[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.

[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

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

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

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.

[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