My Viewsonic VX924 monitor died!

[Rtech]

Re: My Viewsonic VX924 monitor died!

Whatever you use,ensure that the tolerance ie 'J' on the original capacitor is 5%, that is important in these circuits.

[notrash]

Re: My Viewsonic VX924 monitor died!

I was trying to find a replacement for the poly caps (H154J 250MPP1)
Are these Ok: MKS4F031502E00 WIMA MKS 4 ?

[edit] ok this is a Polyester not a Polypropylene cap...

Thanks.

[jetadm123]

Re: My Viewsonic VX924 monitor died!

Hi,

I tried to look for replacement transistors: will one of these fit?: PBSS4250X or DSC700400L

Thanks.
Martin

Yes, the PBSS4250X should work. Of course, there's always eBay if you want the 2SC4672.

[budm]

Re: My Viewsonic VX924 monitor died!

Yep, those two brown polyester caps are for the Royer oscillator output tuning caps, luckily you did not try to turn on the monitor with new transistors, they would have blown up due to this bad caps.

[notrash]

Re: My Viewsonic VX924 monitor died!

Hi,

C24 is definitely blown up.
Diode looks ok (440 Ohm in forward direction).
Secondaries: ~420 Ohm
C335 was always missing. Doesn't look as it has fallen off.

[selldoor]

Re: My Viewsonic VX924 monitor died!

OMG did you not notice any of that before?


C24 fat red/brown cap (Circle Green) looks bulged might as well get 2 and replace the other one as well

Pink Marked component Diode? has that blown up as well?

Measurements are now a secondary problem I cant see where the secondaries are on the back - They should be where I have marked in red on the front. Instead you can measure each of the lamp sockets - marked in blue. Pwer off for 5 minutes meter on ohms 2000 report results

On the back is c335 missing? looks like something was soldered on there?

EDIT

Silly me the measuring points are under the four globs of glue - the sight of the board must have given me a nasty shock. A lot of it is going to need re-soldering

[notrash]

Re: My Viewsonic VX924 monitor died!

Hi,

Nice...and so fast.
Thanks for all the answers.

I think the transistors are the bad parts. One has a hole, and one fell apart when i tried to unsolder it (see last picture).

I can't see a picture when looking at the screen with a flashlight (but the power LED is still on). And yes, the voltages were measured with everything connected.

I tried to look for replacement transistors: will one of these fit?: PBSS4250X or DSC700400L

Thanks for all the additional measuring tips...but i don't exactly know which parts you are talking about. So maybe you could mark them in the picture.

I hope the pictures are good enough.
About my skills and tools: I'm a physicist, working at a university. I learned a bit about electronics...and we have all sorts of measuring equipment and power supplies. And my soldering skills....just look at the pictures ...need improvement (although i had no proper soldering iron).

Thanks.
Martin

[Rtech]

Re: My Viewsonic VX924 monitor died!

As Sonic pointed out, the main areas of failure on these,are 2 0r more of the transistors on the underside, go short circuit,the Inverter transformers have a high failure rate, check by checking the resistance of the secondaries acorss the pins,and the orange./brown Poly caps next to each transformer.if one looks swollen compared to the other that will be faulty as well, and usually goes hand in hand with its associated failed transformer.The transisitors originally 2SC4672,although obsolete, can still be obtained with some searching.I have used FCX1053ATA,which are NPN,3A,75V,sot89 in lieu with no problems at all.

[budm]

Re: My Viewsonic VX924 monitor died!

It looks like this?
http://s807.photobucket.com/albums/y...sonic%20VX924/
Make sure to check the electrolytics caps, the transistors, and the tuning caps (gray rectangula caps for value and reisitance leakage) for the Royer Oscillator used in this inverter circuits, if these caps are bad, they will take out the transistors.

[selldoor]

Re: My Viewsonic VX924 monitor died!

Welcome to the forum Notrash-
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, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say a bit about yourself - skills tools etc.

Next test would be to check the secondary windings on the two inverter transformers.

Meter on Ohms 2000 or autoranging check across the two pins on the end opposite the 6 pins

[Scenic]

Re: My Viewsonic VX924 monitor died!

Check the 4 inverter transistors on the backside of the board (Q6, Q7, Q8, Q9) for shorts

My Belinea 101910 (which uses the same PSU board) died on me while using it a couple months back.
One of those transistors was shorted and actually had a hole in it. When you tried powering it up, the backlight would just flash for a bit less than a second (inverter shut down), but the monitor stayed on (green power LED)

Replacing all 4 of them and resoldering the inverter transformers should bring it back to life.

According to the Belinea Servicemanual (parts list on page 61, inverter on page 46), Q6-Q9 are 2A 50V NPN transistors in SOT-89 package, specifically 2SC4672 by Rohm.

Keyword for these dying POS inverters is "royer oscillator". Searching for that on here will bring up a metric f*ckton of BenQ and Dell LCD monitor threads.. all of them with more or less the same problem.

[selldoor]

Re: My Viewsonic VX924 monitor died!

@Notrash - Do you see an image of what is on the pc when the screen goes black.
try with a flashlght

When you tried to test the voltages was it all connected up

[notrash]

Re: My Viewsonic VX924 monitor died!

Hi,

Great board.
Good to see that i'm not the only one with this problem.

As described I replaced all the caps on the board. I also replaced the two parts mounted on the heatsinks.
But still... if i start my PC the screen looks normal for ~1s and then goes black (as described by bo2000).
The green power LED always stays on.

I tried to measure the voltages at the connector to the second board. One of the top pins shows 12V the other two ~0V...

Any solution for this problem yet?

Thanks,
Martin

[bo2000]

Re: My Viewsonic VX924 monitor died!

Hi Bo,

Welcome to the forum and great job on the clear pics.

Do you have a spare working CCFL that you can use to do a few tests?

Thank you!

I don't have a CCFL but a multimeter if that helps.

What have you done with the main filter Cap in the middle?

Yeah, I know it looks odd, but I only got one of these:

and I had to extend the feet to get it connected to the board.

[Jasgriff]

Re: My Viewsonic VX924 monitor died!

What have you done with the main filter Cap in the middle?

[Jasgriff]

Re: My Viewsonic VX924 monitor died!

Hi Bo,

Welcome to the forum and great job on the clear pics.

Do you have a spare working CCFL that you can use to do a few tests?

[bo2000]

Re: My Viewsonic VX924 monitor died!

Hi!
I found this thread with google.
Awesome board!

I got an old VX924 from work to play with.
The problem was: You can turn it on, it shows a picture for about 1 second, then it wents black. The green power LED stays on.
When you remove the VGA- (or DVI-) cable and put it back on, it also shows a picture for ~1s and turns black again.

Now I changed all the caps like described, but the problem is the same.
But I just noticed, that I forgot one cap. C320. Could that be the problem?

I also checked the polarity and the connection of the new caps.
The logic board gets 12V steady.

2 pictures of my board attached.

Thanks in advance for your help and greetings from Germany

[Perineum]

Re: My Viewsonic VX924 monitor died!

Using the DC adapter to give it power via the capacitor nearest the 6 pin connector resulted in the monitor turning on once and then not again.

When I removed the connector it resumed it's normal non-working behaviour.

I did not have the AC plugged in at the same time as the adapter. Is AC needed at the same time?

[Perineum]

Re: My Viewsonic VX924 monitor died!

I would like to report that the 12 volts from the PSU is fluctuating.

I would guess that the logic board is OK as the image looks fine for the half second it is up on the screen.

Am I still looking at a capacitor problem?

[Perineum]

Re: My Viewsonic VX924 monitor died!

Post some in focus photos of your power supply front and back,using managed attachments.

All the pictures are here: https://www.badcaps.net/forum/showpo...50&postcount=3

The blinking PLED could be caused by voltages coming and going, Maybe from an overload on the power supply causing it to start and stop.
Are there any voltages listed at the connector from the power supply to the logic board.
If they are printed on the board what are they and are they steady?

Sorry for the long delay, I've been working 12 - 15 hour shifts right now. I will measure voltages when I can (soon hopefully). However, I did score a 4.5 amp 12 volt power supply so I can try that as well.