Viewsonic VX715 problem

[mathog]

Re: Viewsonic VX715 problem

I will dig up a DVI cable and see if the VX715 is really better that way.

I could not see any difference between DVI and VGA inputs. This seems to be purely a panel response time limitation.

[mathog]

Re: Viewsonic VX715 problem

http://reviews.cnet.com/lcd-monitors....html?tag=rnav

esponse Time (slower the better?) of monitor is 25.0 ms as per specifications.

Thanks for that helpful link. Quote: low-average heavy-ghosting image on analog VGA (D-SUB) mode. Yup, that's how I would describe it too. Guess that's just the way they are then.

For response time, the faster the better. Ideally if the scan speed is N Hz you want the real response time to be << 1/N seconds, so that the image has no ghosting between frames. For 60 Hz that's 16.67 milliseconds, so ghosting is expected on a display with 25 ms response time. (And they usually cheat on the response time, giving it for the fastest transition, when it should be for the slowest one.) The 5ms Viewsonic monitor on my desk displays no evident ghosting when dragging text windows around, because 5 << 16.67. I will dig up a DVI cable and see if the VX715 is really better that way.

[newbie1]

Re: Viewsonic VX715 problem

The repaired VX715 was attached to a computer and put into use. Static images are beautiful. However, it seems to have a pretty slow refresh rate. For instance, dragging a text window around causes the letters to thicken and darken. As soon as the window stops moving it is beautiful again. Is this typical for this model? I never saw the display on this unit before repairing it, so don't know if there is still something more that needs to be done, or that's just as good as it gets. Oddly, I could not see anything wrong when watching videos, but maybe I just have not found one yet that exposes the issue.

Details:
1280 x 1024 @ 60Hz.
VGA connector (there is no DVI on the graphics card)

Note that only the moving window on the screen has issues, the static part looks fine while this is going on.

unfortunatley, the LCD is no longer with me now for me to verify this. I also could not recall having the same experience probably because i do not drag around a text window much. But looking at other users review here >
http://reviews.cnet.com/lcd-monitors....html?tag=rnav
they are also seeing the same for analog connection of this monitor. Maybe you could borrow a graphics card with a DVI to confirm whether the 'ghosting' is there for DVI as well. fyi Response Time (slower the better?) of monitor is 25.0 ms as per specifications.

[mathog]

Re: Viewsonic VX715 problem

Details:
1280 x 1024 @ 60Hz.
VGA connector (there is no DVI on the graphics card)

Note that only the moving window on the screen has issues, the static part looks fine while this is going on.

[mathog]

Re: Viewsonic VX715 problem

The repaired VX715 was attached to a computer and put into use. Static images are beautiful. However, it seems to have a pretty slow refresh rate. For instance, dragging a text window around causes the letters to thicken and darken. As soon as the window stops moving it is beautiful again. Is this typical for this model? I never saw the display on this unit before repairing it, so don't know if there is still something more that needs to be done, or that's just as good as it gets. Oddly, I could not see anything wrong when watching videos, but maybe I just have not found one yet that exposes the issue.

[newbie1]

Re: Viewsonic VX715 problem

When C923 came out I noticed that there were ink "+" "-" marks on the board reversed with respect to the top surface etch marks. The capacitor had been in with polarity matching the ink. Flipped the board over and sure enough, the ink marks were correct. This was easy to see since one side went to a large common ground which C922, C924, and C925 also used. Apparently there was a small error in the board design, with those top surface markings being backwards. Sorry, no pictures.

C923 on mine was the same. The ink marks are right, but they are not visible until the cap comes off. The surface etch, on the other hand, is visible around the base of the capacitor, so on close inspection it does look like that capacitor is in backwards.

Powered up and it works.

I was really confused when i had to replaced C923 back then. but decided to follow the 'etch marks' instead. I do wonder why on earth didn't they remove the 'etch marks'?.. hhhmmm.. Or could this board be mass produced to be so called universal & can used on other LCDs as well?.. Anyway, i am not as sharp or smart enough as mathog to check that the one side went to a large common ground which C922, C924, and C925 also used. But on a positive note, i get to experience personally 'popping' an electrolytic cap... ..

[mathog]

Re: Viewsonic VX715 problem

Switch off & on again, it now becomes the classic 3 sec to black..
so I inspected the board again, did some touch-up soldering on some components
but was surprised to see the other 1000uF/16v cap (the one standing up)
-ve is facing the heatsink while I saw clearly on the PCB marking printed that it was supposed to be -ve facing outwards.. YIKES!
desoldered it,.. another surprise comes,
beneath it there is a marker pen indicating -ve is should be facing the heatsink,..
confused..

C923 on mine was the same. The ink marks are right, but they are not visible until the cap comes off. The surface etch, on the other hand, is visible around the base of the capacitor, so on close inspection it does look like that capacitor is in backwards.

[mathog]

Re: Viewsonic VX715 problem

Replaced all of the electrolytics on the PS/inverter board other than the big one:

C922 1000uF 16V (Elite)
C923 1000uF 16V (Elite)
C924 470uF 16V (Hermei)
C925 470uF 16V (Hermei)
C906 22uF 50V ("crown symbol")
C207 4.7uF 50V (TL)
C201 150uF,25V (Hermei)
C223 150uF,25V (Hermei)

with equivalent Panasonic FM. For C201,C223 used the 35V part.

When C923 came out I noticed that there were ink "+" "-" marks on the board reversed with respect to the top surface etch marks. The capacitor had been in with polarity matching the ink. Flipped the board over and sure enough, the ink marks were correct. This was easy to see since one side went to a large common ground which C922, C924, and C925 also used. Apparently there was a small error in the board design, with those top surface markings being backwards. Sorry, no pictures.

The Panasonic FM was a little tall for C923, so I put it in sideways. It probably would have been OK vertically, but it stuck up about a millimeter higher than the tallest heat sink, so I didn't want to risk it not fitting if the shield was a tight fit.

Powered up and it works.

[mathog]

Re: Viewsonic VX715 problem

It is customary to put the DMM on DC when measuring DC voltages, AC only when measuring AC.

My analog multimeter at home has an inline capactior for the AC voltage measurement so a DC voltage under the AC doesn't matter. Which is handy since it can look at a cap and show 10V (on DC) and 5V ripple (on AC). It doesn't look like the DMM at work is like that though.

[PlainBill]

Re: Viewsonic VX715 problem

Ah, I missed that, thanks.

When the display is plugged into 120V, with or without a video signal applied, the 12V line is at 13V (DC) when the LED is lit, and falls to 4.5V when it is off. That is measured across C922 or C924. The 5V is doing something similar, up to 5.1V, down to 0.7V, also in sync with the LED. The cycle is about 2 seconds on, 2 seconds off.

Edit: Both the 12V and 5V oscillate between 27V and 10V when the multimeter is set on the 200V AC range.

It is customary to put the DMM on DC when measuring DC voltages, AC only when measuring AC.

Had a 470uF 25V sitting around from the last repair. Put it in parallel with C922. Powered on. Backlight lit and stayed on, at least for the 10 seconds I ran that test. I could see the "no signal" message too.

I'm going to replace bigger caps and I think all should be well.

Be smart and replace all of the electrolytics (except the 450 volt one). That way you won't have to open it up again in a few months.

PlainBill

[mathog]

Re: Viewsonic VX715 problem

Had a 470uF 25V sitting around from the last repair. Put it in parallel with C922. Powered on. Backlight lit and stayed on, at least for the 10 seconds I ran that test. I could see the "no signal" message too.

I'm going to replace bigger caps and I think all should be well.

[mathog]

Re: Viewsonic VX715 problem

Look at post #19, there is a link to the service manual, which includes the schematic and parts list.

Ah, I missed that, thanks.

When the display is plugged into 120V, with or without a video signal applied, the 12V line is at 13V (DC) when the LED is lit, and falls to 4.5V when it is off. That is measured across C922 or C924. The 5V is doing something similar, up to 5.1V, down to 0.7V, also in sync with the LED. The cycle is about 2 seconds on, 2 seconds off.

Edit: Both the 12V and 5V oscillate between 27V and 10V when the multimeter is set on the 200V AC range.

[PlainBill]

Re: Viewsonic VX715 problem

Sure, but I don't have a camera with me right now. Near as I can tell these two boards really are identical. The only difference I can see between this one and the OP's blurry top side photo is that mine has heat discoloration near the sideways capacitor and the OP's did not. All the other locations where mine has heat discoloration the OP's does too, although it is hard to tell in that picture.

Look at post #19, there is a link to the service manual, which includes the schematic and parts list.

If you look at this as a circuit, this is the same design that is used in the Dell (Benq) monitors.

Now a piece of information that might help. A defective CCFL will usually result in a brief flash; sometimes even the display might be on for several seconds. Absolutely no flash usually indicates the inverter is not getting power.

PlainBill

[mathog]

Re: Viewsonic VX715 problem

It is always best to post pictures of your board. While they may look similar to the ones already posted, they are not identical.

Additionally, the OP's picture of the power/inverter board is totally out of focus.

Sure, but I don't have a camera with me right now. Near as I can tell these two boards really are identical. The only difference I can see between this one and the OP's blurry top side photo is that mine has heat discoloration near the sideways capacitor and the OP's did not. All the other locations where mine has heat discoloration the OP's does too, although it is hard to tell in that picture.

[retiredcaps]

Re: Viewsonic VX715 problem

Replace the Elites and the Hermei's and hope for the best?

It is always best to post pictures of your board. While they may look similar to the ones already posted, they are not identical.

Additionally, the OP's picture of the power/inverter board is totally out of focus.

[mathog]

Re: Viewsonic VX715 problem

I just picked up one of these at work. When powered on the power LED comes on after a few seconds, then cycles, but the backlight doesn't light up, not even for a second at first power. Following this thread I checked the resistance on pins 1->7 on both output transformers, and they were NOT shorted. Inspected the 4 transistors and they were not (obviously) blown.

The circuit board is a little toasty looking though. It is discolored under the two sets of 4 resistors next to the output transformers. (I can sort of see the same thing in the OP's picture.) The board around L201 and L202 is slightly brown. Underneath the sideways Elite, L903 and D910 and D911 it is also a bit brown.

The same capacitors are present as noted by the OP, again with the sideways Elite a bit swollen. The other Elite and the Hermei's look are not swollen, and no blown bottom plug.

I think this one is probably not quite so far along as the OPs. It seems not to have blown (yet) the C5706 transistors. I'm wondering if maybe it isn't just a bad lamp? Of course the connectors are completely different from all of the other displays I have, so that will be a bit hard to test.

What are those blue caps in the output circuit? They are marked 7C184J: 250VoR. I could not read the capacitor specification for it in the attachment earlier in this thread. They look suspiciously like the capacitors I had to replace on a failed Sharp TV.

Replace the Elites and the Hermei's and hope for the best?

[newbie1]

Re: Viewsonic VX715 problem

I would love to see a picture of the soldering above. Just curious and may need to do something like that in the future.

Glad you got the monitor working.

oh man!.. should have snap it before closing up..

to be honest, it is tricky, a bit of 'touch-n-go' & sure doesnot look pretty...
what i did was firstly using a plier, i 'un-bent' pins 1 & 3 of the C5707 (type 7303-003, see attachment).. then i applied some solder to the shorter Pin 2..
i then cut a pin from the faulty C5707 & apply some solder on it.. using a tweezer i align it to the shorter pin 2 & quickly heat them-up with the solder to join them together.. quite tedious as u need steady hands to hold the tweezer & the other hand to quickly heat them.. too much solder & it won't fit in the hole.. too less & the extension lead will drop off.. if your alignment is off-set, then the pin will be crooked... sigh!,, took me around 15-30min to successfully manage to get 2 C5707 to fit properly.. the protusion of Pins 1 & 3 out of the holes will also be lesser.. but as for mine, i can see the Pins 1 & 3 tip on the other side, so i assume it should be safe contact... i guess.. Actually, my plan B if this doesnot work, is to use a wire to extend the 'Collector' hole from the board & solder it to the heatsink of the C5707.. because from the datasheet Pin 2 (the shorter pin) & the heatsink (Pin 4) are both 'Collector'.. maybe some other experts here have a better way than what i did..

[retiredcaps]

Re: Viewsonic VX715 problem

however, managed to extend the middle lead by soldering the old leads ontop of the new c5707s & re-soldered them onto the board

I would love to see a picture of the soldering above. Just curious and may need to do something like that in the future.

Glad you got the monitor working.

[newbie1]

Re: Viewsonic VX715 problem

*updates

c5707s arrived today.. but., horror upon horror... they are not the through hole type... sigh!.. .. ..

however, managed to extend the middle lead by soldering the old leads ontop of the new c5707s & re-soldered them onto the board,.. double confirmed using DMM that Pins 1-7 of PT202 are no longer shorted.. yay..

power-up the baby &... 'ITS ALIVE! ITS A.L.I.V.E.!'.. no more '2 sec to black'.. ..

my greatest appreciation goes to
- retiredcaps, PCBONEZ, Dgtech & of course, last but not least,

>> Mr PlainBill..

u guys are awesome!!.. .. ..

[newbie1]

Re: Viewsonic VX715 problem

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?

*thanks. noted on the resoldering of the transformers.. hhmmm.. i could not see anywhere on the board printed with a BENQ.. or maybe, age is catching up, & i need glasses.. btw, loved your "troubleshooting 2sec to black" thread..

I just wonder sometimes what the real percentages (failure rates) are of some of these monitors/tv's. For people to sell "repair kits" suggest a real demand. I guess there probably just are not enough failures to create a recall.

Congrats on your find and have fun with it. Let this be the first of many fixes.

*thanks man, i do not want to celebrate too soon.. not until, i have replaced the parts & the problem doesnot happen again..

From what I understand, the C5707 is an upgrade (probably higher voltage) from the C5706. I have a very limited experience with these monitors, but have heard that the C5707s work perfectly.

PlainBill

*i am still waiting for the C5707 to arrive, likely to be middle of next week to update again.. Hope you are right again about it,,, AS ALWAYS!..

If you don't do the work yourself they cost more to fix than to replace.
... And most people don't solder.

*very true indeed, sir,.. plus, i believe the 3-years warranty for a new screen + new technology (LED screens) are making pple NOT to repair the panels.. and they usually want to upgrade to a bigger screen in 2-3 years..