My Viewsonic VX924 monitor died!

[selldoor]

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
http://www.badcaps.net/forum/attachm...1&d=1290283049

http://www.badcaps.net/forum/attachm...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

[budm]

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.

[Rtech]

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.

[notrash]

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

[selldoor]

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]

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.

[budm]

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.

[jetadm123]

Originally Posted by notrash

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.

[notrash]

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.

[Rtech]

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