viewsonic VX724 help needed

[cnkay]

Well hello 1st post on this forum but sure seems like the place to be!

Have a VX724 display died power light blinking. Once every 5secs or so very quick picture flicks on but would not say lite. So I opened unit and found three caps bad. 470uF (2) were like 19uF and one 330uF was 8uF. Replaced those. no dice same symptoms found two burned up transistors on back side. I believe that I found an older post with correct Rohm transistor numbers so I ordered them (.74 each) and tried it again. As soon as I plugged it in and started to lift screen from the workbench the same transistors on backside were smoking. Don't have the numbers I order handy but I remember they were marked DK. I think they were 50V 3A NPN.

Does anyone have the schematics for this unit?? Could you help me with the correct transistor number??

Could I have a broke or shorted bulb or something else that would take out these transistors? Looks like two identical circuits and nothing else jumping out at me. Trying to compare one side to the other.

I do remember if I powered unit up with only two of the four CN1-4 wires plugged in that I did get a picture just not that bright. I am guessing that there are two or four bulbs inside.

Any help would be most welcome, as I am currently unemployed and could use losing this monitor like a cracked tooth. CoL

Thanks MUCH
Chris

[Solder Boy]

Re: viewsonic VX724 help needed

A photo of the board would be helpful.. top and bottom shot. Something is causing the transistors to short out.

If you do a search of this forum you will see that just replacing the obvious bad capacitors often isn't good enough.

Sounds like you have a capacitance meter, check all of the rest of the caps..if you have an ESR meter you need to check the caps for those readings.

Other veteran repairers will chime in I'm sure..

[PlainBill]

Re: viewsonic VX724 help needed

Well hello 1st post on this forum but sure seems like the place to be!

Have a VX724 display died power light blinking. Once every 5secs or so very quick picture flicks on but would not say lite. So I opened unit and found three caps bad. 470uF (2) were like 19uF and one 330uF was 8uF. Replaced those. no dice same symptoms found two burned up transistors on back side. I believe that I found an older post with correct Rohm transistor numbers so I ordered them (.74 each) and tried it again. As soon as I plugged it in and started to lift screen from the workbench the same transistors on backside were smoking. Don't have the numbers I order handy but I remember they were marked DK. I think they were 50V 3A NPN.

Does anyone have the schematics for this unit?? Could you help me with the correct transistor number??

Could I have a broke or shorted bulb or something else that would take out these transistors? Looks like two identical circuits and nothing else jumping out at me. Trying to compare one side to the other.

I do remember if I powered unit up with only two of the four CN1-4 wires plugged in that I did get a picture just not that bright. I am guessing that there are two or four bulbs inside.

Any help would be most welcome, as I am currently unemployed and could use losing this monitor like a cracked tooth. CoL

Thanks MUCH
Chris

Try the Belinea 101910 service manual. It's available at www.elektrotanya.com.

The inverter uses a Royer oscillator, the same design used in the infamous Benq monitors sold under the Dell and HP labels. And it's subject to the same failures.

The one most often mentioned - the solder joints on the transformer legs crack. Remove the old solder and replace. Referring to the Belinea schematic, the tuning caps C24, C25 (0.15uF 160V) are critical. Make sure the solder joints on them are good. The Schottky diodes D9, D10 (2A 40V) have also been mentioned as culprits.

PlainBill

[dasjeetu]

Re: viewsonic VX724 help needed

Hi!

Happy to help. Please find it in



Please download....

Thanks.
Jeetu