View sonic VX924

[Lakerat]

Hi,
I have this LCD that blew the 100UF400v cap and a lot of others. board looks dark where cap let loose..I replaced all caps and both of the poly propane caps near the edge.. Monitor flashes power light and when hook up to comp. screen flash's but no viable picture

I can not get photo's until this weekend
Any idea what I might look for?

[Lakerat]

Re: View sonic VX924

I found the values of the poly propane caps from a older thread .(cap are brown in color) it said the tolerance is to be 5% The new caps have a higher voltage and a 10% tolerance
would this be causing this symptoms
I had to replace both because one cap was split open. I thought better to keep them alike

[PlainBill]

Re: View sonic VX924

I found the values of the poly propane caps from a older thread .(cap are brown in color) it said the tolerance is to be 5% The new caps have a higher voltage and a 10% tolerance
would this be causing this symptoms
I had to replace both because one cap was split open. I thought better to keep them alike

Odds are the driver transistors are shorted. When you attach the pictures I'll point them out if you haven't already identified them.

PlainBill

[Lakerat]

Re: View sonic VX924

How do I check transistors for shorts? The caps I bought were from my local electronics store (NOT RATSHACK). could this be doing it?
When hooked up to comp. it acts like the power button does not work on monitor due to flashing on screen..only turns off when power cord is unplugged

[retiredcaps]

Re: View sonic VX924

How do I check transistors for shorts?

If you have a manual ranging multimeter, set it to 200 (two hundred) ohms. Touch the black and red probe together. It should read 0.3 or 0.4 ohms. If it is higher than 1.0 ohm, there is something wrong with your multimeter.

If your multimeter reads "1" or "OL", it means the measurement is outside your chosen range. Don't confuse "1" on the left hand side of this display with 1.0 on the right hand side. The first means out of range and the second means 1.0 unit of your measurement.

You can test for shorted transistors "in circuit" (with power off and unplugged)

a) put black probe on pin 1 and red probe on pin 2 - read/record ohm
b) put black probe on pin 1 and red probe on pin 3 - read/record ohm
c) put black probe on pin 2 and red probe on pin 3 - read/record ohm

If any ohm reading is less than 50 ohm you might have shorted transistor. Remove the transistor and repeat the tests out of circuit to verify.

[PlainBill]

Re: View sonic VX924

How do I check transistors for shorts? The caps I bought were from my local electronics store (NOT RATSHACK). could this be doing it?
When hooked up to comp. it acts like the power button does not work on monitor due to flashing on screen..only turns off when power cord is unplugged

Pictures, pictures, pictures!!!

the inverter in this monitor uses two circuits called 'Royer Oscillators'. If you look at the top of the board you will see two poly caps, two inductors, two transformers. On the back of the board you will see two sets of two transistors, two sets of two diodes, etc.

A Royer oscillator works well in an inverter. It is efficient, easy to build, and reliable - until something goes wrong. A poly cap splitting open will alter the operating frequency of that oscillator, causing the transistors to short. (Actually, the cap probably shorted, causing the split). That will cause the symptoms you describe. Basically, the shorted transistors overload the power supply.

Part of the problem is you are not supplying adequate information. You replaced the 100uF, 450 volt cap. Presumably you used a good quality part; most 100uF, 450 volt caps will work well. Which other caps did you replace? If you replaced the electrolytic caps on the power supply output did you use low ESR caps? If you didn't, that will also cause problems.

PlainBill

[lucky13]

Re: View sonic VX924

Lakerat,

Welcome to badcaps.

Please also update your profile so we know what continent you are in.

[thraxarious]

Re: View sonic VX924

Sorry to jump in and Necropost here, but I was browsing idly on this model and came across something appearing the same as what I have going on here, and thought I would toss some pictures into the mix.

The monitor is one I picked up for recycling, and the power board looks kinda bad, so I was considering ditching this monitor. It looks like it might be a bit of work, and the board may be done with due to what appears a lot of leaked electrolytic fluid all over the place.

There's a lot of darkening around the Q320 and the main cap is done with.

[selldoor]

Re: View sonic VX924

1. See the post above yours.

2. There was a post sometime in the last week about electrolyte on boards
If you enter electrolytic into the search above you will find it.

3Welcome to the forum-
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors.

Have you plugged it in and turned it on ? did it do anything
Can you tell if the panel is good? (cracked)
Are you happy to spend time trying to get it to work.
Do you have a multimeter and soldering equipment and know how to use them

[Rtech]

Re: View sonic VX924

Lots of the caps have failed by the looks of the bulging ones !!!,is the staining really from the big cap?? not so sure about that.These boards do get very hot and discolour, the inverter drive transistors on th back of the board usually go short circuit, other faults are the Inverter transformers and the Brown Poly caps next to to them.So a lot to check if you are considering repair ??

[thraxarious]

Re: View sonic VX924

1. See the post above yours.

2. There was a post sometime in the last week about electrolyte on boards
If you enter electrolytic into the search above you will find it.

3Welcome to the forum-
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors.

Have you plugged it in and turned it on ? did it do anything
Can you tell if the panel is good? (cracked)
Are you happy to spend time trying to get it to work.
Do you have a multimeter and soldering equipment and know how to use them

Yeah, finally got around to setting a few things for my profile there. I mostly do this on the side as a hobby. I've gotten a few nice monitors out of it.

Trick here is I am moving and I have to reduce what all I am taking. Sadly a few projects have to be handed over to someone else or recycled.

I hadn't even turned it on, it was given to me to recycle. The panel is in good shape, else I would not have taken it in... just needs caps and possibly some other bits. The rather deep darkening on the board had me worried though whether it was worth giving it a shot or handing it to someone else with more time on their hands.

[retiredcaps]

Re: View sonic VX924

It looks like it might be a bit of work, and the board may be done with due to what appears a lot of leaked electrolytic fluid all over the place.

Wow, I don't have decades of experience, but I have seen my fair share of pictures here and I have NEVER seen one like yours before.

[budm]

Re: View sonic VX924

Believe it or not, I recap the PS/MAIN board and check the Tuning caps, it works just fine after that.
Too many pictures to post:
http://s807.photobucket.com/albums/y...sonic%20VX924/

[selldoor]

Re: View sonic VX924

Ok - so you need to clean the board up a bit then let us know if you want to have a go.
I would test the inverter transformers as these can be expensive to replace relative to the cost of a used working or semiworking 19".

[Scenic]

Re: View sonic VX924

As a test if the "rest" of the monitor is still OK, you can inject 12V externally.

Get rid of the bad caps around the L-shaped heatsink and solder two wires in place of a cap. Viola.. there's your 12V injection point (mind the polarity). Needs at least 3A or the backlights won't stay on, even if the inverter works properly.
I'd leave the one cap that doesn't appear to be bulging in place for that test. All four of them are in parallel on the 12V output of the PSU.

That way, you can at least check if the inverter and logicboard are still alive, or if the panel has a crack that you can't see without the backlight on.
Crude but effective.

[Rtech]

Re: View sonic VX924

A Power supply from an Old Computer, would give you the 12v as suggested, if you are going to try that.

[thraxarious]

Re: View sonic VX924

I did try a light rinse and aggressive dry, which did remove some crud from surrounding contacts. I may decide to just try the dishwasher trick described in one of the posts on the electrolytic leak discussion.

Is anyone sure the edges of the board won't absorb any of the water between the layers of the PCB? it looks like it may be a bit porous.

Its looking like it may be a bit more work than I want to get into with around a month to go before I have to pack the car and move. I just hate to ditch a possible good monitor it could be made to work again.