ViewSonic VX2260WM not working

[Rtech]

Re: ViewSonic VX2260WM not working

Because it is odd, I would try and separate the circuits ie, lift the two Diodes that supply the Inverter voltage,and then measure the 5V line, that may give some idea of what is happening.

[robehickman]

Re: ViewSonic VX2260WM not working

Lifted the two diodes and confirmed 0v on the ccfl inverter side. To begin with it started up in the same flashing power LED. Took a reading across the big cap which now shows 335v.

At exactly the moment I took the reading on that cap the power LED switched to its usual continual on state, weird. Now when it's plugged/unplugged it goes straight to standby led and the on/off button appears to work as usual.

Voltage across the 5v supplies show 6.15v on USB and 6.13v both of which are stable. Is this too high?

[Rtech]

Re: ViewSonic VX2260WM not working

Perhaps some help then !! The 6.15v is most certainly because there is no load,which would drop that down towards the 5v.as it is stable it would seem that part of the circuit is fine.You need to start looking at the inverter side now,starting with the 2 x Diodes themselves.With Power off,and your meter set to Diode test if you have it,measure both diodes,Black on the end marked with the white Band, Red on the other, then reverse the leads,and advise what you get,and the part code on the diodes.

[selldoor]

Re: ViewSonic VX2260WM not working

This seems to be getting more and more complex - while the diodes are lifted
would be a good time to check them.
"7.3) Bad Diode

Diodes (D or ZD designation) can be bad. To test a diode in circuit,

a) put your multimeter in diode test mode
b) put your black lead on one side and the red lead on the other - record reading
c) reverse the leads - recording reading

A good diode should read 0.4V to 0.7V in one direction and 0L in the other. If you get a reading in both directions, you will have to desolder one leg and retest to verify."

This test and others are in retiredcaps guide to 2 seconds to black. This can be found here https://www.badcaps.net/forum/showthread.php?t=10419 start at post 19.

Would worry too much about the voltage on the BIG cap - it is should be
about 1.4 times mains so if that varies between 230 and 240 depending on time of day day of week useage etc the cap voltage will change.

I am out of ideas though you can check the mosfets (that component I ringed earlier (burnt2)) on the back of the power board for shorts - see the 2 sec to black for instructions. You can also try and clean it up with some isopropyl alcohol to find the part number - it should also be on the other one nearby.

[selldoor]

Re: ViewSonic VX2260WM not working

If you dont have a diode test setting then use this:
Set the meter to its ohms range - any range should do, but the middle ohms range if several are available is probably best.

Connect the cathode terminal of the diode to the terminal marked positive on the multimeter, and the anode to the negative or common terminal.

Set the meter to read ohms, and a "lowish" reading should be obtained.

Reverse the connections.

This time a high resistance reading should be obtained.

[robehickman]

Re: ViewSonic VX2260WM not working

Have checked the diodes and they appear to be all right, putting them back in.

Would a dead ccfl cause these symptoms?

-----------------------

edit:

After re-setting the diodes it seams to be working again, comes on/off as expected and the back lights are all working. Wander what was up, have to see if it keeps working.

[selldoor]

Re: ViewSonic VX2260WM not working

I dont know - if it was just a dead ccfl it would not cause these symptoms but it is
difficult to do any tests other than visual on a ccfl except by substitution.
Usually if one lamp has gone when you switch it on you get a flash - hence the dark room test
I did wonder if a wire had come off and was shorting on the frame? if you can get to the lamps you can have a look.

Haha -just seen your edit. Perhaps a cold solder joint on the diode. Leaving it on will test it for a bit but so will switching it off and back on A/ when it is warm and B/ when it is cold. If you can leave it on for now in case the others want you to test anything while it is on. Have you got it connected to a pc- is thre an actual picture or just back light?

[Rtech]

Re: ViewSonic VX2260WM not working

Have checked the diodes and they appear to be all right, putting them back in.

Would a dead ccfl cause these symptoms?

-----------------------

edit:

After re-setting the diodes it seams to be working again, comes on/off as expected and the back lights are all working. Wander what was up, have to see if it keeps working.

A dry joint maay have caused the problem....leave it on, and lets see if it stays on !!

[budm]

Re: ViewSonic VX2260WM not working

So what DC voltage do you get in the inverter power supply now? It did not sound right on your first report.