Viewsonic VA721 LCD - Power and Inverter Board

[PCBONEZ]

The combo Power Supply and Inverter board has all 'Elite' brand caps of various model lines. [The video board has different brand caps, all small and non-vented types, and they 'look' good. - Don't anticipate problems on that board.]

[7] EB(M) -brown- 4 of 5 on Inverter side are bad, 2 on PS side 'appear' okay
[1] PW(M) -black, w/vents, huge- 'appears' okay
[4] PF(M) -black, no vents, small diameter, 4mm- 'appear' okay
[1] ??(?) -black, w/vents- 'appears' okay

The EB(M) break down:
[2] 16v-1500 'appear' okay (only EB(M)'s fully on the power supply side.)
[1] 10v-1500 'appears' okay (only non-bloated EB(M) on the Inverter side.)
- the bad boys - all in Inverter or between Inverter and PS-
[1] 10v-1500 bloated and vented BAD.
[1] 10v-1000 bloated and vented.
[1] 16v-470 bloated.
[1] 16v-470 bloated with blown out bung.

~~~~

If they went cheap on all their Inverter boards and you don't mind doing caps then Viewsonics with bad back-lights may be a good source of cheap LCD screens.

.

[Sparky]

Re: Viewsonic VA721 LCD - Power and Inverter Board

Pics?

You could probably use some rubycon caps from Topcat to replace those caps, I'd do them all personally.

BTW, I have a viewsonic LCD (VX2025wm), 1 year 4 months old, no problems. Has a 3 year warranty so not worried about anything. It is a great screen.

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

It's dated Oct 2004 so it blew out at about 30-32 months old.
You may NEED that warranty!

This one belonged to a co-worker friend of my wife's. She LIVES on the computer but her only back-up 'part' is an older laptop I rebuilt for her last year for when she goes to visit her dad up north. (Can't live without her Internet for two whole days!)

Don't think she knew it was still under warranty... Or cared...
It was an excuse get a wide screen so she ran out an bought a 19" the same day it went bad.

I got the dead one as a "if you can fix it you can have it" kind'a thing.

I didn't realize it was under warranty either but to tell you the truth I'd rather replace the caps then deal with an RMA and all that hassle anyway.

~~~~~~

Just to be complete:
(In case someone needs a caps list for this screen.)

[1] PW(M) -black, w/vents, huge- 'appears' okay
---- 400v-100uf
[4] PF(M) -black, no vents, small diameter, 4mm- 'appear' okay
---- 50v-22uf
[1] ??(?) -black, w/vents- 'appears' okay
---- 35v-100uf

The black ones are probably fine but they are all "Elite" brand and I don't wanna take this freakin' thing apart again so I'm gonna replace them too.

......

I don't need Rubycon's for this.
People are telling me FC's or PM's are enough.

Found everything I need (diameters, pin spacing, and all that) at Digikey for $6 flat. - Only one (the 400v) is over 47 cents.
Except for the 400v and 35v all are NI-HE/UCC-KY (or better).
I found an FC for the 35v and a KMG for the 400v.
-- (Which are both in the first stage of the PSU so I don't care that much about ESR as long as they aren't crap caps.)

Since I have to do an order anyway I'm gonna make a cap list for a few motherboards I've been putting off doing and maybe save a little on shipping.


.

[Sparky]

Re: Viewsonic VA721 LCD - Power and Inverter Board

I forgot about the panasonics, yeah those would work well. Only reason I suggested rubies was that is what Topcat has besides the Samxons and I haven't ordered anything from digikey at all so I forgot about it.

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

Here, all in one place.

[Qty] / Volts / uf / diameter / lead spacing / color of original

[1] 10v-1000uf-8mm-3.5mm-brown
[2] 10v-1500uf-10mm-5mm-brown
[2] 16v-1500uf-10mm-5mm-brown
[2] 16v-470uf-8mm-3.5mm-brown
[1] 35v-100uf-8mm-5mm-black
[4] 50v-22uf-5mm-5mm(on pcb, leads are bent to fit)-black
[1] 400v-100uf-18mm-7.5mm-black
-- There are two of the 22uf in the PSU section and two in the inverter. (No vents.)

As I said the black ones may not be a problem I'm just replacing them with better ones since I'm in there anyway.

The brown ones ARE a problem.

Hope this helps someone.

.

[davmax]

Re: Viewsonic VA721 LCD - Power and Inverter Board

It seems as though this thread started somewhere else. It does not say what is wrong with the product. I presume it is dead.

Dead LCD monitors are quite often not related to caps. If it does not start at all it is most likely two resistors from the high voltage input that create a feed to allow starting. It is common for these to go high. If this is the problem read their values and then substitute three resistors of about the same value. This is achieved by inserting two of the replacements in the original places then cutting the track that connects them at the common point and finally solder the third resistor so that it bridges the broken track. The three resistors will distribute voltage stress and lengthen life.

Hopefully this is useful.

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

davmax

Thank you for the input.

I've repaired dozens of LCD screens for laptops. (I refurbished laptops for a couple years as a part time home business). - But with those I can usually find complete inverters for under $15 so I just swap-out rather than repair them.

Haven't done much with desktop LCD's so I don't have a feel for what to look out for in them.

To check those resistors is a 'good to know' little fact.

~~~

On this one the original caps are bloated and vented.

A bit of google searching suggested this is a common problem in early 2000's LCD's. (And in Viewsonic.)

Since I had it apart I made a parts list in case anyone else has to make up their mind about fix or replace on one of these.

~~~

The two pairs of resistors measure fine but darkening of the PCB material under them the does indicate they are getting extremely hot.

I may do your suggested mod to spread out the heat as a preventive measure. (Or maybe just replace with higher watt resistors and mount with some air-space to the PCB. Room isn't a problem on this PCB.)

.

[davmax]

Re: Viewsonic VA721 LCD - Power and Inverter Board

Interesting that your device shows two hot resistors. I have only fixed two LCD monitors and their resistors were of high value 100s of kohm and not hot. It has been my experience over many years that despite the voltage rating of about 250V that high value resistors will go higher resistance if stressed with a continuous high voltage. I suspect the quality of the product may also be a factor. So increasing to three resistors has a two fold gain. 1. Moves the resistance value down range and 2. Reducing the voltage across each resistor. Hopefully this will provide a better lifetime.

If you discover more I will be interested.

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

I just woke up, I hope this makes sense.

These are probably not resistors for the same function as the ones you had problems with then.

These are 10 ohms and I think 1/8 watt. (May be 1/16 watt.)

There are two transformers in the output to the CCL's. (One for each lamp)
- The xfmrs are about 1.25" x 3/4" x 1/2" tall.
- Case material has the same finish as a magnet and there's a steel? frame around it.
- I think they are xfmrs. I can't find the PN anywhere but the board is marked T901 and T902 for them. (PN: TLT-1016 4929 K)
- They look like multi-tapped xfmers on the input but are wired like a single center tapped xfmr by connecting the taps together.
- The output side is a single winding. (Or has taps clipped where I can't see it.)

These are each followed by an inductor and a few film caps on the CCL side. No resisters in there unless they are SMD on the underside of the board and those appear to be part of filters back to ground or feedbacks and not part if the load line.

The resistors of concern are on the input side of those tranformers (2 per xfmr 4 total) and they are set up like a voltage divider with the point the two resistors have in common being the center-tap of the xfmr and the overall divider being across the xfmr's outer taps. (All of this is after the section with the bad caps.)

- So, in this circuit, putting a resister in between and in series with the other two won't work. I can't cut the trace because the center tap is in there too and there is no way to split that.

The don't seem to be an actual problem (yet) except they are getting hot.
So I'm thinking I'll just up the wattage to 1/4 watt and call it good.

...

With the bad caps in there my CCL voltage is jumping up and down between about 150 and 400 volts. (Unloaded, I don't wanna blow my tubes.)
- It's hard to check anything for sure at this point.

.................................
Is there any way to put photos in here now?
I don't like to use 3rd party sites (including mine) to post photos.
If the 3rd party goes away the pic turns into an empty box here.

.

[tinkerdude]

Re: Viewsonic VA721 LCD - Power and Inverter Board

I SWEAR to God, the answer to everything is on the Internet somewhere. It's just a matter of searching it out.

Yes, I too came into possession of a Viewsonic VA721 with bad caps (got it for free as well). The display was very dim overall, especially on the right left side. Opening it up, I saw that all 4 CCFL lamps were lit only part way across. Thought it might be a bad inverter yielding low voltage. A few searches later, I was at this site and wondered whether I might be dealing with bad caps, just as PCBONEZ was. Sure enough, once I dug out the PS/Inverter board, those damn bulging and venting Elite caps were obvious.

Question is, PCBONEZ, after replacing all the Elite caps, was your VA721 good as new? I'm perfectly capable of doing the same thing, but obviously I'm curious to discover whether your repair worked.

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

I've now done two Viewsonics (different models) where all that was needed was new caps.

[tinkerdude]

Re: Viewsonic VA721 LCD - Power and Inverter Board

I've now done two Viewsonics (different models) where all that was needed was new caps.

Rock on! Just completed the repair. My (free) VA721 is now good as frickin' new. I just replaced the 5 brown Elite's on the inverter side:

C825 (1000uF, 10V, 8mm diameter, 15mm length, 3.5mm lead separation)
C903 and C910 (470uF, 16V, 8mm diameter, 12mm length, 3.5mm lead separation)
C824 and C828 (1500uF, 10V, 10mm diameter, 15mm length, 5mm lead separation)

The last two looked fine, but I replaced them anyway since they evidently are known to crap out (see above in previous posts).

Parts cost: $3.07

Note well that this is not a simple repair. Not recommended for beginners, a little dicey for intermediates (though no problem for advanced or professional folks, I'm sure). I'd say I'm intermediate, but I didn't have much to lose - I got the damn thing for free.

Then again, much is now known about this repair. Your mileage may vary.

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

Congrats!!!

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

On the VA721 I did the PCB was double drilled so that vitally every spot (probably all, I don't remember for sure) could use either 3.5mm or 5mm lead spacing.
-
Was yours like that too?

[tinkerdude]

Re: Viewsonic VA721 LCD - Power and Inverter Board

On the VA721 I did the PCB was double drilled so that vitally every spot (probably all, I don't remember for sure) could use either 3.5mm or 5mm lead spacing.
-
Was yours like that too?

I do remember that for most if not all the caps I replaced, the PCB was double-drilled (maybe one wasn't). I didn't measure the spacing, but that sounds about right.

[vinbar1]

Re: Viewsonic VA721 LCD - Power and Inverter Board

I was given the same moniter. When I cracked it open I found 5 bulged and leaking caps.

c822 1500uf 16v
c823 470uf 25v
c824 1000uf 10v
c825 470uf 16v
c903 470uf 16v

I could find them all localy except one the 1500uf v16 so I replaced it with a 2200uf 16v I was not sure this would work but I figured i payed nothing for the moniter and I realy wanted to see if I could actuly get it fixed. This was the first time I have done any soldering. well it worked just fine. I don't know if it will blow or do something crazy. but for now its good.

Its awesome!! and fun!! I am getting my son into it and now we are looking everyplace to find moniters to fix LOL.

Thanks so muck for this forum its great!!!

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

Congrats!!!
I think your alternate will do just fine.

[Zolton]

Re: Viewsonic VA721 LCD - Power and Inverter Board

Greetings All,

I too happened up this thread however in not such a direct way. Two years ago + - I replaced a failing VA721 with with a new Samsung Syncmaster 225BW. The VA721 had been growing dimmer each day and was at the point I could no longer use it. I remember searching various sites for remedies but found little information. I put the VA721 in the closet where it collected dust for 2 years.

While my 225BW was still under warranty, recently, I began to have problems. It would turn on for 1 second and then turn off. I contacted Samsung who of course advised that I could ship it to them along with my original purchase receipt and they would be glad to perform service. The fact that round trip shipping and packaging would cost $50 + was moot because i no longer had the receipt. Anyway, I began to search for information on the 225BW but found little. That's when I happened upon this thread. I retrieved my Va721 from the closet opened it up and viola just like Tinkerdude said bad caps at C825 C824 C 903 C910 and C828. Having had a similar problem with a Mitsubishi big screen last year, http://www.techlore.com/forum/thread/19407/Mitsubishi-WS-65813-Blinking-Green-Light/ I already had experience replacing capacitors. I had also purchased a de-soldering tool from Radio Shackhttp://www.radioshack.com/product/index.jsp?productId=2062731 I highly recommend this tool. I would also like to add the following link to a dis assembly guide for the VA 721 http://fileshare.eshop.bg/downloadsm/6598/jean_ve710s-2.html My Va721 now works like new. Thanks to all who posted useful information.

My 225BW in now working again too and I will post repair information in a new thread. Sorry for the lengthy post and thanks for your help.

[xathan]

Re: Viewsonic VA721 LCD - Power and Inverter Board

I was given the same moniter. When I cracked it open I found 5 bulged and leaking caps.

c822 1500uf 16v
c823 470uf 25v
c824 1000uf 10v
c825 470uf 16v
c903 470uf 16v

I could find them all localy except one the 1500uf v16 so I replaced it with a 2200uf 16v I was not sure this would work but I figured i payed nothing for the moniter and I realy wanted to see if I could actuly get it fixed. This was the first time I have done any soldering. well it worked just fine. I don't know if it will blow or do something crazy. but for now its good.

Its awesome!! and fun!! I am getting my son into it and now we are looking everyplace to find moniters to fix LOL.

Thanks so muck for this forum its great!!!

i have the same problem here, i can't find 1500uf v16 anywhere in our place. the dealer told me that its possible to use 1500uf v25 but not with different uf. but luckily they don't have v25 too. they have only 2200uf 16v. will this really work? thanks

[PCBONEZ]

Re: Viewsonic VA721 LCD - Power and Inverter Board

That depends on what the cap does and what else is in the circuit.
Can't say yes or no just based on the cap values.
Have to analyze the circuit to make swaps like that.
-
You could try it and 'see what happens' but there's nothing certain either way.
~Probably~ wouldn't actually blow anything up just trying it, but it might work like sh*t, not start, or have gremlins.
Just depends on what the cap does.
.