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**retiredcaps** · 07-08-2010, 09:26 AM

Re: Viewsonic VX715 problem

1) Use your dmm and test each component. You can test many components without the power plugged in. Use ohm to look for shorts in transistors and transformers.

2) I learned by looking at videos on youtube. You can search by entering

how to measure transistor using dmm
how to measure transformer using dmm
how to measure diodes using dmm
etc
etc

The front pic of the board is way out of focus. Take this board to a window on a sunny day and put your camera on macro mode. This will yield nice clearly focused pictures.

Here is a pic I took next to the window. It is top down and you can see everything clearly.

https://www.badcaps.net/forum/attach...chmentid=16690

3) What brand of capacitors did you use to replace the bad ones.

Originally posted by newbie1

Got a Viewsonic VX715
symptom - screen display flashing every 2-3 sec,

1)how do I know, did I fried the transformer or any other components?
2)Where do I need to measure (resistance or voltage) to determine whether to change any other components?

i've attached the images of the power board.. apologies if its not good enough

**retiredcaps** · 07-08-2010, 09:48 AM

Re: Viewsonic VX715 problem

Originally posted by newbie1

so I inspected the board again, did some touch-up soldering on some components

BTW, some of the solder joints look suspect to me in the photo. See

http://workmanship.nasa.gov/lib/insp...uirements.html

on what good/bad joints look like.

**Dgtech** · 07-08-2010, 11:11 AM

Re: Viewsonic VX715 problem

If you are lucky, you just blew the cap that you turned around and a fuse. If the unit was working at any point with the cap in the position that you found it, you should have kept it in that same position. I hope you didnt blow anything else. The first thing I would do is simply this. In your first post you said that you had replaced one obvious bad 1000uF/16v cap. You should have changed them all. Second, correct the polarity of the one cap - put it back the direction you found it in. Third, check the fuses - you may have to replace one if it's blown. After you do those things, power it up and see what you got.

**newbie1** · 07-08-2010, 08:42 PM

Re: Viewsonic VX715 problem

Originally posted by retiredcaps

1) Use your dmm and test each component. You can test many components without the power plugged in. Use ohm to look for shorts in transistors and transformers.

2) I learned by looking at videos on youtube. You can search by entering

how to measure transistor using dmm
how to measure transformer using dmm
how to measure diodes using dmm
etc
etc

The front pic of the board is way out of focus. Take this board to a window on a sunny day and put your camera on macro mode. This will yield nice clearly focused pictures.

Here is a pic I took next to the window. It is top down and you can see everything clearly.

https://www.badcaps.net/forum/attach...chmentid=16690

3) What brand of capacitors did you use to replace the bad ones.

Originally posted by retiredcaps

BTW, some of the solder joints look suspect to me in the photo. See

http://workmanship.nasa.gov/lib/insp...uirements.html

on what good/bad joints look like.

Thanks for all ur replies & guidance...

1) updates

measured the below (power unplugged)
*F901 (circled blue) - short
*transformer - (i labelled them in red in the pix attached)
shorted > points 1-2, 1-3, 2-3, 4-5, 6-7
fluctuating resistance (600k) > points 4-6, 5-6, 5-7
open > all other points

now i realized i missed F201, and all the transistor (measure C to E, right?)...
will update when i get back home

2) thanks for sharing.. the pix is awesome.. pity i took them at night.. as again will try to take a better one when i get back home

3) i changed the 1000uf/16v to nichicon (that is what available here) & 470uF/16v to KME (that is what is stated on the caps).. hope they are fine

noted on the solder joints.. will try to resolder them again,,,

Originally posted by Dgtech

If you are lucky, you just blew the cap that you turned around and a fuse. If the unit was working at any point with the cap in the position that you found it, you should have kept it in that same position. I hope you didnt blow anything else. The first thing I would do is simply this. In your first post you said that you had replaced one obvious bad 1000uF/16v cap. You should have changed them all. Second, correct the polarity of the one cap - put it back the direction you found it in. Third, check the fuses - you may have to replace one if it's blown. After you do those things, power it up and see what you got.

hope i am lucky..
& noted on changing ALL the caps AT THE SAME TIME... heee... thanks...

yes i have put them the correct way it was first seen.. it is now still 3-sec-to-black screen..

funny things is even though the cap is reversed or not it is still 3-sec-to-black screen.. am i missing something?..

Attached Files

**PCBONEZ** · 07-08-2010, 08:57 PM

Re: Viewsonic VX715 problem

I think you are not using low ESR caps.

If the old caps are Elite brand then get rid of all of them.

**newbie1** · 07-08-2010, 09:20 PM

Re: Viewsonic VX715 problem

Originally posted by PCBONEZ

I think you are not using low ESR caps.

If the old caps are Elite brand then get rid of all of them.

Hi sir,

yup got rid of both the 1000uf/16v Elite caps & replace them with nichicon..

as for the 470uf/16v (i am not sure what brand, but they are purple color) & replace them with KME

btw, may i know how to tell it is low ESR or not..
bought them at an electronic component store here..

**retiredcaps** · 07-08-2010, 09:46 PM

Re: Viewsonic VX715 problem

Yes, test the transistors for shorts using ohms.

Originally posted by newbie1

now i realized i missed F201, and all the transistor (measure C to E, right?)...
will update when i get back home

**retiredcaps** · 07-08-2010, 09:47 PM

Re: Viewsonic VX715 problem

Originally posted by newbie1

btw, may i know how to tell it is low ESR or not..

You need an ESR tester. They cost anywhere from $40 to $60. I personally can't justify the cost for fixing monitors since buying caps are cheaper.

Nichicon makes a variety of caps. Some are low ESR and some are not.

**PCBONEZ** · 07-08-2010, 11:54 PM

Re: Viewsonic VX715 problem

You tell if caps are low ESR by looking in the data sheet.

Each caps brand has many series' [models] just like automobile manufactures make various models [trucks, hatchbacks, sedans, sports cars, etc].

You have to state both the manufacturer and series for us to know what the caps are.

You used a Nichicon -what- ... you didn't give series
You used a -what- KME. ... you didn't give manufacturer.

I can guess KME.
Both Chemicon and Sam Young [and maybe others] make a KME series.
For Chemicon and Sam Young I know they aren't low ESR because ESR is not even given in the data sheet for KME.
[Sam Young copycats several Chemicon series'.]

The viewsonics I've done have had two series of Elite.
For one series I replace with Panasonic FC [or Panasonic FM if I can't find an FC to fit].
For the other lower ESR series I use Panasonic FM [or Rubycon MBZ or Panasonic FL or FJ if I can't get an FM].

As to where to get data sheets, use google or ask someone here.
[Some crap brands you may never find data for.]

.

**newbie1** · 07-10-2010, 04:05 AM

Re: Viewsonic VX715 problem

Originally posted by PCBONEZ

You tell if caps are low ESR by looking in the data sheet.

You used a Nichicon -what- ... you didn't give series
You used a -what- KME. ... you didn't give manufacturer.

sorry for my limited knowledge on the caps..

ok here its whats printed on the caps >
nichicon 1000uf/16v H 0439 VZ(M) 105C
KME 420uf/16v 7N 4(9) (M) 105C

nyway,
updates (sorry it is a long read)

* measure for shorted (unplugged)
- fuse F201 > shorted
- all transistors (C-E) > not shorted
- C213 & C214 are shorted on board, but desolder one of them & it measured open.. so i assume they are ok?!

read in one of the thread to measure the voltage going into the CCFL, with POWER plugged, when the screen is 'ON' state, just before it goes blank.

so decide to build the courage to do so.. GULP!..

*measure volt (just before it goes blank) on
CON201 (red circle) and CON202 (pink circle)

>CON201=2.64V
>CON202=3.7mV!!!!!!!! hmmmm..

continue tracing the line & saw 2 components (not sure whats its called)
linking to them-
Q203 to CON201
Q204 to CON202 (with less voltage)..

so i measured the line before (blue circle) and after (light blue circle) them
*measure volt (screen blank)
>Q203 (blue) =13V
>Q203 (light blue) =0V
>Q204 (blue) =13V
>Q204 (light blue) =0V

*measure volt (when screen ON)
>Q203 (blue) =12.1V
>Q203 (light blue) =8.5V
>Q204 (blue) =12.1V
>Q204 (light blue) =12.1V ????

marking on them

4411
BE3424

found the datasheet it is AO4411 (FET), no?
http://www.aosmd.com/pdfs/datasheet/AO4411.pdf

unplug the board,
*measure pins 1-8 on both Q203 & Q204, all with same result
> pins 4 not shorted to any other pins
> pins 1-3 all shorted
> pins 5-8 all shorted

questions:
1) am i right to say only Q204 is faulty?.. since CON201 (Q203 linking to it) is showing 2.64V to the CCFL... or both are faulty?
2) any other volt measurements do i need to measure?

thing is,
firstly am not sure whether i can get the parts locally here (S'pore),
saw some on ebay, but not sure its pricey or not with, shipping of course

secondly de-solder & soldering the parts will be tricky for me, esp there are smd parts near them.. sigh!..

any inputs are greatly appreciated..

hope u guys have a great weekend,,,

Attached Files

**newbie1** · 07-17-2010, 02:29 AM

Re: Viewsonic VX715 problem

updates

* i replaced Q204 with IRF7406PBF & the 2 470uf/16v KME with panasonic fc but with 470uf/25v,, and the result is still 3sec-blank
* i unplugged the power & measure resistance D202 shows 242ohms both ways, unsolder D201 and solder it on D202 location and confirmed it is still showing the same result (242ohms both ways).
* i continue measuring pin-pin resistance of PT201 vs PT202 using 20k scale
(see yellow circles)
PT201 PT202
Pins 1-8 3.93 0.25
Pins 7-8 0.25 0.25
Pins 1-7 3.61 0.00

the other pins 2-3-4-5 (shorted=0.00) and pins 1-6 (shorted=0.00) are the same on both PT201 and PT202.. would appreciate if anybody could confirm that the readings i took above is showing that PT202 is faulty?.. or isit something else shorted/open?!?!..

Attached Files

**Dgtech** · 07-17-2010, 06:21 AM

Re: Viewsonic VX715 problem

Whenever you posted these measurements, you seemed as if you were on the right path.

>Q203 (blue) =13V
>Q203 (light blue) =0V
>Q204 (blue) =13V
>Q204 (light blue) =0V

*measure volt (when screen ON)
>Q203 (blue) =12.1V
>Q203 (light blue) =8.5V
>Q204 (blue) =12.1V
>Q204 (light blue) =12.1V ????

What I would do in this case is swap the CCFL plugs and see if the problem voltages stay the same or does Q203 get the voltages of Q204 and vice versa after the CCFL's are swapped. This will give you some indication. One of the circuits are not firing due to bad lamps or bad circuit.

**PCBONEZ** · 07-17-2010, 12:38 PM

Re: Viewsonic VX715 problem

Originally posted by newbie1

sorry for my limited knowledge on the caps..

ok here its whats printed on the caps >
nichicon 1000uf/16v H 0439 VZ(M) 105C
KME 420uf/16v 7N 4(9) (M) 105C

No one knows much about caps when they first get started.

What I am trying to get across is that you look up data for the OLD caps.
From that information you choose the new caps.

I think you are just telling us the new caps.
The new caps are good brands but I[we] can't know if their specs are better, equal, or worse than the old caps unless you tell us what the old caps were.

Some old caps can't be looked up because cheap brands don't always have a website or publish data sheets. In that case one goes by what is usually found in that kind of circuit. [That's where talking a bunch of people that do this all the time helps a lot.]

BTW: For a first try at thing you are doing very well.

.

**newbie1** · 07-18-2010, 05:28 AM

Re: Viewsonic VX715 problem

Originally posted by PCBONEZ

No one knows much about caps when they first get started.

What I am trying to get across is that you look up data for the OLD caps.
From that information you choose the new caps.

I think you are just telling us the new caps.
The new caps are good brands but I[we] can't know if their specs are better, equal, or worse than the old caps unless you tell us what the old caps were.

Some old caps can't be looked up because cheap brands don't always have a website or publish data sheets. In that case one goes by what is usually found in that kind of circuit. [That's where talking a bunch of people that do this all the time helps a lot.]

BTW: For a first try at thing you are doing very well.

.

thanks for the encouragement,.. fyi, this is the first time i am having trouble after recapping/resoldering... my previous 2 dead samsung works fine after recapping/resoldering,.. i have look thru this fantastic forum & so far reviving vx715 has been successful just by recapping the 2x 1000uF.. or maybe i am wrong.. thats y i need the veterans/masters like yourself to guide me along..

the original OLD caps that were replaced :
2x /16V - Elite ES (M) 105C (C) 0351
2x 470uF/16V - Hermei LT 105C 0348

Originally posted by Dgtech

Whenever you posted these measurements, you seemed as if you were on the right path.

>Q203 (blue) =13V
>Q203 (light blue) =0V
>Q204 (blue) =13V
>Q204 (light blue) =0V

*measure volt (when screen ON)
>Q203 (blue) =12.1V
>Q203 (light blue) =8.5V
>Q204 (blue) =12.1V
>Q204 (light blue) =12.1V ????

What I would do in this case is swap the CCFL plugs and see if the problem voltages stay the same or does Q203 get the voltages of Q204 and vice versa after the CCFL's are swapped. This will give you some indication. One of the circuits are not firing due to bad lamps or bad circuit.

i did swap the CCFL plugs, & CCFL is not the issue (i.e CN202 no volt & Q204 output (pins5-8) is 12.1V).. now i managed to get hold of the schematic & i am feeling anxious.. i am suspecting that one of the inverter-transformer (PT202) is *kaput*,busted,shorted, dead.. or so i believe.. my reading, in the previous post, shows PT202 Pins 1-7 is shorted (0.00) while PT201 Pins 1-7 (3.61 @ 20k scale).. but looking at the schematic, as attached (see arrows), Pins 1-7 are not supposed to be shorted!!!???... i hope the schematic/circuit experts here can help me confirm this before i splashout further $$ on a new inverter-transformer..

btw, anyone knows is there any substitute for this inverter-transformer (80AL15T-7-YS or 80LL15T-7-YS)??.. what do u look for when u purchase this component?!. volt? amps?.. or are they repairable?!,..

Attached Files

**PlainBill** · 07-18-2010, 07:41 AM

Re: Viewsonic VX715 problem

Originally posted by newbie1

thanks for the encouragement,.. fyi, this is the first time i am having trouble after recapping/resoldering... my previous 2 dead samsung works fine after recapping/resoldering,.. i have look thru this fantastic forum & so far reviving vx715 has been successful just by recapping the 2x 1000uF.. or maybe i am wrong.. thats y i need the veterans/masters like yourself to guide me along..

the original OLD caps that were replaced :
2x /16V - Elite ES (M) 105C (C) 0351
2x 470uF/16V - Hermei LT 105C 0348

i did swap the CCFL plugs, & CCFL is not the issue (i.e CN202 no volt & Q204 output (pins5-8) is 12.1V).. now i managed to get hold of the schematic & i am feeling anxious.. i am suspecting that one of the inverter-transformer (PT202) is *kaput*,busted,shorted, dead.. or so i believe.. my reading, in the previous post, shows PT202 Pins 1-7 is shorted (0.00) while PT201 Pins 1-7 (3.61 @ 20k scale).. but looking at the schematic, as attached (see arrows), Pins 1-7 are not supposed to be shorted!!!???... i hope the schematic/circuit experts here can help me confirm this before i splashout further $$ on a new inverter-transformer..

btw, anyone knows is there any substitute for this inverter-transformer (80AL15T-7-YS or 80LL15T-7-YS)??.. what do u look for when u purchase this component?!. volt? amps?.. or are they repairable?!,..

First, I have to congratulate you on your persistence. It's refreshing to see someone with limited electronics knowledge who is willing to really WORK at learning about electronics troubleshooting rather than simply giving up. Also, thanks for supplying a schematic. It makes this a LOT easier.

Here's a quick lesson in troubleshooting. You found pin 1 and pin 7 of PT201 shorted. Pin 7 is one end of the secondary winding, pin 1 is one end of one of the primary windings. These two winding would normally be well insulated from one another; the secondary produces the high voltage (700-1000 volts) for the CCFLs. Also, the secondary usually has a high resistance - 1K or greater. So, lets assume it's not the transformer or the other end of the secondary.

Where does that leave us? Well, where is pin 7 connected? To ground!!! Now, look at pin 1. Where is it connected? To the base of Q209 and to a pair of 2K resistors. It is very rare that resistors short, but how about transistors? Well, they do short out, and what's more, the emitter of Q209 goes to ground.

Now, this circuit is very common for anyone who has worked on monitors, particularly Dell monitors. It's called a Royer oscillator. And it's well known because it is quite common to find the two C5706 or C5707 transistors shorted!!! The last little tidbit? A transistor is very tiny. It is difficult to fit the full part number, so manufacturers often skip the first two characters - which are always 2S for bipolar transistors. And the schematic says these are 2SC5706 transistors.

So try removing both of them from the board and see if the short from pin 1 to pin 7 of PT201 goes away.

Now the other encouraging news. One common cause of these transistors shorting is bad solder joints on the transformers. So it was not caused by anything you did. But you WILL want to resolder the pins on both transformers before trying the monitor.

PlainBill

**PCBONEZ** · 07-18-2010, 01:18 PM

Re: Viewsonic VX715 problem

Elite spec sheets are here. [Just googled "Elite Capacitor"]
http://chinsan.co.th/category.asp?cat_id=2&type_id=1
ES is here:
http://chinsan.co.th/files/ES.pdf
It's a Low ESR cap.
1000uF 16v comes in 10x20mm and 10x25mm
10x20mm ESR=0.030 , Ripple=1250
10x25mm ESR=0.030 , Ripple=1280
You want ESR the same or less
You want Ripple he same or more
Nichicon VZ aren't rated well enough
http://nichicon-us.com/english/products/pdf/e-vz.pdf
VZ are not Low ESR [hence no ESR rating]
The 100uF 16v only tolerates 560 Ripple.
Also 105C temp rated caps are preferred [they last longer].
[They should last long enough to trouble shoot but I would put in better caps before closing it up and calling it good.]

Hermei is here:
http://www.hermei.com.tw/catalog_e.htm
Found the same way - some brands are harder and other just can't be found.
http://www.hermei.com.tw/2006/7LT.pdf
470uF 16v - Low ESR - Ripple 920
Here is KME
http://www.chemi-con.com/files/KMEKMEH9.pdf
KME measures ESR at 120Hz vs 100kHz and so isn't comparable.
[They do that for some caps intended to be used on AC.]
So just look at the Ripple - It's 370 so KME is also not rated as good as the original cap.

ESR is -like- resistance only it is specifically resistance to ripple passing through the cap. Since filter caps are used to 'send' ripple to ground [to get it out of the circuit] lower ESR is better.

The Ripple rating is how much Ripple can pass through the cap without overheating it's internals. A higher Ripple rating amounts to a heavier duty cap.

.

**newbie1** · 07-18-2010, 08:11 PM

Re: Viewsonic VX715 problem

Originally posted by PCBONEZ

Elite spec sheets are here. [Just googled "Elite Capacitor"]
http://chinsan.co.th/category.asp?cat_id=2&type_id=1
ES is here:
http://chinsan.co.th/files/ES.pdf
It's a Low ESR cap.
1000uF 16v comes in 10x20mm and 10x25mm
10x20mm ESR=0.030 , Ripple=1250
10x25mm ESR=0.030 , Ripple=1280
You want ESR the same or less
You want Ripple he same or more
Nichicon VZ aren't rated well enough
http://nichicon-us.com/english/products/pdf/e-vz.pdf
VZ are not Low ESR [hence no ESR rating]
The 100uF 16v only tolerates 560 Ripple.
Also 105C temp rated caps are preferred [they last longer].
[They should last long enough to trouble shoot but I would put in better caps before closing it up and calling it good.]

Hermei is here:
http://www.hermei.com.tw/catalog_e.htm
Found the same way - some brands are harder and other just can't be found.
http://www.hermei.com.tw/2006/7LT.pdf
470uF 16v - Low ESR - Ripple 920
Here is KME
http://www.chemi-con.com/files/KMEKMEH9.pdf
KME measures ESR at 120Hz vs 100kHz and so isn't comparable.
[They do that for some caps intended to be used on AC.]
So just look at the Ripple - It's 370 so KME is also not rated as good as the original cap.

ESR is -like- resistance only it is specifically resistance to ripple passing through the cap. Since filter caps are used to 'send' ripple to ground [to get it out of the circuit] lower ESR is better.

The Ripple rating is how much Ripple can pass through the cap without overheating it's internals. A higher Ripple rating amounts to a heavier duty cap.

.

PCBONEZ, my great appreciation for taking time explaining, in details, the caps specification...

noted on the nichicon (1000µf).. will try not to forget to replace them before completing the job. . oh, & fyi, the NEW KME (470µ) was replaced with a pair of NEW Panasonic EEUFC1E471...

**newbie1** · 07-18-2010, 08:39 PM

Re: Viewsonic VX715 problem

Originally posted by PlainBill

First, I have to congratulate you on your persistence. It's refreshing to see someone with limited electronics knowledge who is willing to really WORK at learning about electronics troubleshooting rather than simply giving up. Also, thanks for supplying a schematic. It makes this a LOT easier.

Here's a quick lesson in troubleshooting. You found pin 1 and pin 7 of PT201 shorted. Pin 7 is one end of the secondary winding, pin 1 is one end of one of the primary windings. These two winding would normally be well insulated from one another; the secondary produces the high voltage (700-1000 volts) for the CCFLs. Also, the secondary usually has a high resistance - 1K or greater. So, lets assume it's not the transformer or the other end of the secondary.

Where does that leave us? Well, where is pin 7 connected? To ground!!! Now, look at pin 1. Where is it connected? To the base of Q209 and to a pair of 2K resistors. It is very rare that resistors short, but how about transistors? Well, they do short out, and what's more, the emitter of Q209 goes to ground.

Now, this circuit is very common for anyone who has worked on monitors, particularly Dell monitors. It's called a Royer oscillator. And it's well known because it is quite common to find the two C5706 or C5707 transistors shorted!!! The last little tidbit? A transistor is very tiny. It is difficult to fit the full part number, so manufacturers often skip the first two characters - which are always 2S for bipolar transistors. And the schematic says these are 2SC5706 transistors.

So try removing both of them from the board and see if the short from pin 1 to pin 7 of PT201 goes away.

Now the other encouraging news. One common cause of these transistors shorting is bad solder joints on the transformers. So it was not caused by anything you did. But you WILL want to resolder the pins on both transformers before trying the monitor.

PlainBill

Hi Mr Plain Bill...

.. for the record, i am one of your fan...

.. have been following ur posts silently all the while.. i am honoured to receive a congratulation from you..

what can i say,.. you are SPOT-ON.. i did not notice any physical defect on Q212, because it was facing the big blue caps,.. but since you mentioned it, i did a close-up look again & the black top part is *CRATERED/BLOWN*.. i de-soldered them & it was measuring open on all pins but still inverter transformer (PT202) pins 1-7 shorted.. removed the other Q211, and PT202 pins 1-7, is NO longer shorted...

.. measured Q211 B-E is shorted, which is what you are trying to tell me, i believe.. ok, now to get the replacemnts, any thoughts on replacing the 2SC5706 with 2SC5707?

link to 2SC5707> 2sc5707

for the record, schematic of Viewsonic VX715 can be found here
> vx715

Attached Files

**retiredcaps** · 07-18-2010, 10:32 PM

Re: Viewsonic VX715 problem

Originally posted by newbie1

ok, now to get the replacemnts, any thoughts on replacing the 2SC5706 with 2SC5707?

The c5707s are mainly used on boards made by Benq and they are often shorted. You can see the many posts on this subject. Resoldering the transformers on the benq boards is recommended.

I can't tell from your blurry power/inverter pic in post #1, but does it say Benq anywhere on the board?

I'm fairly sure you can replace the c5706 with a c5707, but I'll let PlainBill confirm.

You can find many sellers on ebay selling the c5707 separately or as a "kit" to fix Benq monitors. The kit usually comprises of 4 c5707s, 3 fu9024, and 1 picofuse 3A/125V.

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