ViewSonic VX922 and VX724 Bad CapXon

[hackerbob]

I have two LCD monitors both flashing power led, no picture.

Both units have Bulging CapXon caps. I have decided to repait these myself but the vx724 looks to have some darkening( not burnt ) of the PS board around one of the the CCLs transformer and Q320(vx724). I am wondering if I should replace those too.

Anyone re-capped these PS boards and have a parts list? Some caps I cannot read because they are blocked and I know one is covered with a thermal shield of some sort.

Rob

[EGuevarae]

Re: VierwSonic VX922 and VX724 Bad CapXon

I'm about to receive 3 Viewsonic Monitors and I think that one of them is a VX922. Please, if you can, post a pic of the boards. If it is the same, I can try to identify the ones you want.

[hackerbob]

Re: VierwSonic VX922 and VX724 Bad CapXon

Here is the VX922 PS board. There is a cap c123 I do not know the value of.

[EGuevarae]

Re: VierwSonic VX922 and VX724 Bad CapXon

UPS is going to deliver the 3 ViewSonic at around 2pm. I'll get back to you ASAP when I open them.

[EGuevarae]

Re: VierwSonic VX922 and VX724 Bad CapXon

I have a similar board (from a Syncmaster 173s on which I am working on right now) that has a similar layout. From the picture, taking the design and position into account, my board has a 22mf 50v Sam Young cap there (it is in the same area as the AC input, around the 400v 100mf and the transformer). I had a Sylvania 700p (Proview, rebranded, I think) that had the same similar layout a 22mf 50v too. You can try that, but your best bet is to remove it (you would remove it anyway if you are going to do a full recap). Or you can wait to see if one of my LCDs has that C value more visible.

[EGuevarae]

Re: VierwSonic VX922 and VX724 Bad CapXon

If you see the thread https://www.badcaps.net/forum/showthread.php?t=5992 it says that the cap in question is a 22mf 25v. I mentioned a 22mf 50v. It is OK if you use the 50v, even if it is originally 25v. The V rating is maximum operational limit, not the working voltage, so you are safe. I still can't post pics, but one of the Viewsonics has a 22mf 50v and the other is covered in "the white stuff" and I can only see that it is 22mf.

[nasir]

Re: VierwSonic VX922 and VX724 Bad CapXon


I tried replacing the caps, it didn't work. the screen flickers (light turns on and off). I am sure the data goes through because I could see my desktop and could shutdown my pc.
does anyone have any other ideas?
what about the transistors?
or the lights?


thanks

[PlainBill]

Re: VierwSonic VX922 and VX724 Bad CapXon

I tried replacing the caps, it didn't work. the screen flickers (light turns on and off). I am sure the data goes through because I could see my desktop and could shutdown my pc.
does anyone have any other ideas?
what about the transistors?
or the lights?


thanks

Classic description of a problem with the backlighting system. It could be either the inverter or the CCFLs.

My usual suggestion is to buy a case mod light kit (search for cold cathode light kit on eBay. Use the CCFLs from the kit to test the monitor inverter. Use the inverter from the kit to test the monitor CCFLs.

PlainBill

[Player2]

Re: VierwSonic VX922 and VX724 Bad CapXon

I tried replacing the caps, it didn't work. the screen flickers (light turns on and off). I am sure the data goes through because I could see my desktop and could shutdown my pc.
does anyone have any other ideas?
what about the transistors?
or the lights?


thanks

Replace the transistors on the inverter, your board may have 2 or 4. The markings on the top should be:

DK
QF

Replace with Rohm 2SC4672T100Q, can be ordered from Digi-Key or Mouser.

[kerm007]

Re: VierwSonic VX922 and VX724 Bad CapXon

how did you remove the plastic cover after removing the 4 screws at the back ?

[PlainBill]

Re: VierwSonic VX922 and VX724 Bad CapXon

how did you remove the plastic cover after removing the 4 screws at the back ?

Very carefully. Usually there are latches holding teh two halves together. A thin blade, such as a very small screwdriver or a guitar pick will release the catches.

PlainBill

[kerm007]

Re: VierwSonic VX922 and VX724 Bad CapXon

ok but where do you start after removing the stand ?

Thanks

[kerm007]

Re: VierwSonic VX922 and VX724 Bad CapXon

what part need to be remove the front or the back of cover ?

can you post a pic ?

[PlainBill]

Re: VierwSonic VX922 and VX724 Bad CapXon

what part need to be remove the front or the back of cover ?

can you post a pic ?

It varies. I'm not familiar with that particular monitor,but most recent monitors I have worked on, the front bezel comes off.

Steps to follow:

1. Remove the stand.

2. Working on a padded surface, stand the display on it's top so you can see the groove where the bezel mates with the back.

3. Look for details along the length of the groove which will indicate the presence of latches, or even which part slides inside the other.

4. Using a wide, thin blade such as a very thin screwdriver, a thin guitar pick, etc, release the catches.

5. Work your way around all four edges, releasing the catches and separating the two pieces.

6. If you break something, reflect that perhaps you should have practiced on another monitor.

PlainBill

[Leopard]

Re: VierwSonic VX922 and VX724 Bad CapXon

Fixed a VX922 yesterday. Bad caps were CapXon KF series.
I decided to do a little testing since this board is easy to work on and there is plenty of room for bigger caps.

3x 470uF 25V - replaced with Sanyo WX 1000uF 25V caps
1x 470uF 10V - replaced with Rubycon ZL 680uF 16V cap
2x 1000uF 10V - replaced with Sanyo WX 1000uF 16V caps

Display works like new now.

[Hunt]

Re: VierwSonic VX922 and VX724 Bad CapXon

Fixed a VX922 yesterday. Bad caps were CapXon KF series.
I decided to do a little testing since this board is easy to work on and there is plenty of room for bigger caps.

3x 470uF 25V - replaced with Sanyo WX 1000uF 25V caps
1x 470uF 10V - replaced with Rubycon ZL 680uF 16V cap
2x 1000uF 10V - replaced with Sanyo WX 1000uF 16V caps

Display works like new now.

Thank you for telling us what to use and of a successful conclusion.

Where did you get your Sanyo caps from? I had to get Panasonic instead for the 25v and Rubycon for the 16v 1000uF.

I assume you have gone for larger values to get larger volume and that means larger heat tolerance; but doesn't the larger values have a timing effect or does that not matter in a voltage smoothing circuit?

[kc8adu]

Re: VierwSonic VX922 and VX724 Bad CapXon

it does not matter.not a timing element.
larger,lower esr =longer life.

[Hunt]

Re: VierwSonic VX922 and VX724 Bad CapXon

Thanks for the information guys/gals
Worked perfectly the first time I fired the PC up!
One slight niggle is when I fired the PC up the next day the screen was like a water colour paining were the paint had run
After leaving it on for an while it reverted back the a great picture.
Subsiquent cold starts have been ok.

Any ideas all; as to what the problem could be?

[nuryev]

Re: VierwSonic VX922 and VX724 Bad CapXon

Just completed a successful repair to Viewsonic VX922 - thanks to the detailed instructions and advice provided by people on this site. Another piece of electronic equipment not going to the junk pile - you are all doing your bit to save our planet.

YOU GUYS ROCK!!!!!

Pity we can't desolder and replace some caps to change people's attitudes to waste and pollution.

Thanks everyone for sharing your problems and posting pics of the powersupply boards and caps.

[jsaily]

Re: VierwSonic VX922 and VX724 Bad CapXon

I repaired yesterday a VX724 which was salvaged from the company dumpster.

I have to say that at first the inverter board look beyond repair since the large 100uF / 400V cap had leaked badly and the board was also pretty red due to overheating. All other caps were also bulging. I immediately suspected that the switcher IC (SG6841S) could be damaged because of the primary side cap failure... Strangely enough not even the fuse was blown and all semiconductors tested ok. Replacing all small caps with new low ESR ones and using a transplant 100uF/400V cap from a donor board revived the monitor! The picture is clear and sharp as ever. It's a perfect Christmas gift to my father-in-law!