ViewSonic VX2260WM not working

[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.

[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 !!

[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?

[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

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.

[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.

[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.

[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

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

Thanks for the comments, what (in your opinion) is the probability that changing the caps will fix this, vs it being some other issue.

[tom66]

Re: ViewSonic VX2260WM not working

I think you should have your electrics checked by a qualified electrician - RCDs are safety devices and should not just trip randomly! You could have a loose or intermittent ground somewhere. I have only ever once tripped the RCD, by touching ground and the heatsink of a power supply at the same time. It's painful and I will avoid doing it next time...!

[budm]

Re: ViewSonic VX2260WM not working

That does not sound right at all, 25~30V for 22" LCD backlights inverter circuits, and it also trips the RCD when the board is running by itself (I do this all the time), something is not setup right some where.

[jetadm123]

Re: ViewSonic VX2260WM not working

Very odd. The voltage is too low on the 5V output and would seem a bit high on the inverter output.

[robehickman]

Re: ViewSonic VX2260WM not working

@selldoor the ringed item appears undamaged and has markings, however I cannot read them, the fuses are good.

@budm the voltage of that capacitor fluctuates between 25 and 30 volts. They are both 270uf@50v.

The 4.2v reading is only approximate and does fluctuate as mentioned above. It may start higher than this but my multimeter does not update its display that quickly, so it could drop in the interim.

I did power the board up without the logic board earlier(with the lamps connected) and it it tripped the house's RCD within a second or two, don't want to risk doing that again at this time.

[budm]

Re: ViewSonic VX2260WM not working

I am still learning everyday myself.

[selldoor]

Re: ViewSonic VX2260WM not working

whoops! - thanks budm. I just see a fuse and check them. As you will have gathered I
dont know much about circuitry, but I am trying to learn.

[budm]

Re: ViewSonic VX2260WM not working

@selldoor, they MOSFET for driving the inverter transformer, it is a half-bridge drive setup.
The two PICO fuses are for the USB hub and the logic board, since he is getting 4.2Vdc on pin 1~4, the fuses are OK.

[budm]

Re: ViewSonic VX2260WM not working

Please see the attached pictures, you can power up the board without the logic board connected, but do connect the lamps connectors. Please take a reading of that DC filter cap for the Inverter circuits, you can read it right on the two pins of the cap. I need to see if the voltage is off by the same percentage as the 5V supply.
Also, what is the value of the two caps in red circle on the right of the picture?

[selldoor]

Re: ViewSonic VX2260WM not working

Also there are 2 orange fuses on the power board near the connector to the main board
can you test them. Power off Meter on 200 ohms one probe on each end of fuse.
post result as F802 = ohms F80x = ohms should read the same as holding the probes together.

[selldoor]

Re: ViewSonic VX2260WM not working

Hurrah cavalry has landed, wondered where everyone was. Anyway I have a number of suggestions for purchases but suggest waiting to see what other ideas emerge. You dont have many options - cant see anywhere in Gwent.

Anyway can you have a look at the ringed item in the attached it is a voltage regulator. Question is is it burnt. If so can you read any numbers on it and can you also get the part number of the other one near to it.

I will also add a list of suggested caps from one seller