xerox xa-19i

[Phlox321]

Hi everyone, ive got a weird question, my xerox screen recently died, got the 2second to black problem, ive recaped the entire power supply and inverter section and still nothing, what ive noticed is it has a slight whistle soun when swirched on and gets a bit louder as the ccfls go on and then goes off when ccfls go off after two seconds.

Also is it normal for the backlights to go on briefly when it was switched on with input signal and i test voltage from blon pin and gnd? I mean if i short out the blon pin and gnd next to it the ccfls come on briefly

[budm]

Re: xerox xa-19i

Sounds like high voltage arcing, better check to make sure the lamp connectors are seated properly, bad wire on the lamp assembly, arcing from high voltage winding of the inverter transformer, lamp's ballast caps.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[Phlox321]

Re: xerox xa-19i

Thanx for the reply, it is definately arcing, but on the ccfl tubes itself coz i put on the screens original ones and a test one lying around, the arcing happens ons the pcb itself where the lamp cables are soldered on the pcb.

Any way to fix it? Or is there other damage that causes it to arc?

[Phlox321]

Re: xerox xa-19i

Oh and it still arcs on the pcb even if no lamps are connected

[budm]

Re: xerox xa-19i

"Oh and it still arcs on the pcb even if no lamps are connected" That will cause arcing if no lamps attached, it will go into shutdown after 3 seconds. The start up voltage can be as high as 2000V, so it has to go some where if there is no load, the circuit will detect no lamp and go into shutdown.
I never seen lamps wires soldered directly to the board, they always use sockets. Any pictures? Look at the board in the dark to see if you can see where the arcing occur. Already inspect the high voltage transformers, etc?

[Phlox321]

Re: xerox xa-19i

Im sorry, meant the arcing happens where the lamps wires that has the sockets are solderd to the pcb, ive got pictures but not at pc at the moment, will send tommorow , and how should i tetst the transformers?

[Phlox321]

Re: xerox xa-19i

here's a picture of where the arcing happens

[Rtech]

Re: xerox xa-19i

The solder points are normally covered by some insulating white stuff..have you taken this off,and not replaced it with hot glue etc etc ?/

[Phlox321]

Re: xerox xa-19i

It happened even though that white stuff was on , i only took it off to see why and where the arcing hapend, but it dit arc even with the white stuff, im going to put som hot glue on this afternoon

[Phlox321]

Re: xerox xa-19i

Could it be that the white insulating stuff maybe became loose and that caused the arc that cause the backlights to switch off?, everything else on the board looks fine, and has been completely recapped with new panasonic caps

[Rtech]

Re: xerox xa-19i

The other thing that sometimes happens ,when you are plugging and unplugging the lamps in the sockets,is that the odd pin in the socket can get bent easily..check them as well.

[selldoor]

Re: xerox xa-19i

So were there never any sockets or did you or someone take them off?
Like Budm says I ve never seen lamp wires soldered to the board.

When they first strat there could be 2000 volts on those connections
so almost bound to arc.

[budm]

Re: xerox xa-19i

You MUST completely remove that carbon trace, as you can see it is right next to the other high voltage trace, then seal that area with electronics grade Silicone RTV.
So the manufacturer cheap out by not using the lamp sockets.

[Phlox321]

Re: xerox xa-19i

There are sockets for the lamps but the sockets are on those short wires that is soldered toe the pcb, i removed the carbon and put some hot glue over and inbetween the wires as i dont have and dont know where to buy the electronics grade silicone rtv.

Ive put i back and switched on, doesnt arc anymore at the inverter side but still goes 2 secs to black, but i hear a new squeeling noise coming either from the ac input side somewhere or the inverter transformers

[Phlox321]

Re: xerox xa-19i

Another thing ive just noticed , if its relevant or not, is one of my adaptors thats on a power strip the same one my screen is connected ,doesnt make a proper connection so my desk lamp,goes out when the plug moves slightly, but i saw that when that adapter is jiggled about ever so slightly, theres a click sound on the power\inverter board and the lamps go on for a fraction of a second and then goes of, also i cant seem to get voltage readings when using the power/inverter boards ground, but when i put the black probe on a ground on thr small logic board i get voltage readings on the power board

[selldoor]

Re: xerox xa-19i

I think someone has adapted the board - still if you can get it to work without arcing it will have to do. Post a clear picture of the top and bottom of the board where the Inverter transformers are and we will tell you where to test. I can just see the transformer in your pic but cant work it out from that angle.

[Phlox321]

Re: xerox xa-19i

heres a few pics, hope they're clear enough, I only a phone to take pics , no camera

[selldoor]

Re: xerox xa-19i

OK - not really seen a set up like this I have marked on the attached where I think you can measure the secondary resistance S1 to S2 and S3 to S4 Try that and we will know by the results if that is correct. I have also marked in pink two solder joints that look bad- suggest desoldering and resoldering with unleaded solder.
Also marked in yellow are the joints for 2 high voltage blue caps. Like I said on startup the voltages in that area are very high so all joints must be good and clean. We often advise reflowing all these transformer joints and the blue cap joints as a standard procedure.

[budm]

Re: xerox xa-19i

OK, I have seen this setup before on the no-name monitor. So I will wait the test results that selldoor suggested.

[Phlox321]

Re: xerox xa-19i

Okay so if switched multi meter to 200 ohms, got nothing, switched to 2000 ohms and got a reading of 341 ohms on s1 and s2 and same on s3 s4 also 341 ohms