Viewsonic VX2235WM - blank screen on/off

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

Okay! Something very interesting happened. I connected pin 16 to my multimeter and I get something like 2.61 volts when the monitor is not lit, and 0.06 volts when it is lit. So i ran the PC, played Solitare... The monitor went out and the multimeter still read 0.06 volts. However when I shut the PC down, it lit up saying the no signal message, then went into standby as normal.

[budm]

Re: Viewsonic VX2235WM - blank screen on/off

OK, how about pin 15, did it go low also? I am trying to find out if pin 15 is the Inverter on and pin 16 is the DIMMING control pin or it is another way around. It may be using active LO (LO = Inverter ON)

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

Okay just tested Pin 15, and it stays at 3.01 volts even after the monitor blacks out.

[budm]

Re: Viewsonic VX2235WM - blank screen on/off

So those two signals stay the same when the monitor blacks out, then I would look at the inverter circuits section then.
There is small glass fuse, that fuse is for feeding the B+ to the inverter circuit, see you have DC voltage at both ends measuring against the chassis ground when it is working and when it blacks out.

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

Okay just tested the fuse, and when the monitor is not lit, the voltage is around 23.5 or 24 volts DC. When the screen is lit it drops to 19.2 volts.

When the screen blacked out, it went up to 22.1 volts.

Oh, and voltage readings are the same on either end of the fuse against chassis ground.

[budm]

Re: Viewsonic VX2235WM - blank screen on/off

That is a big drop from 24V. Did you replace any caps in that 24Vdc power supply section, at this point you may need ESR meter to verify the ESR of those caps, the bad cap can have correct capacitance but the ESR can be high.
For example:
https://www.badcaps.net/forum/showth...416#post288703

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

All right. I think I have the caps needed, so all the ones I saw in the pic you posted I'm gonna pop out and put in known good ones.

Okay, just replaced everything except a couple 220uf @ 25 volt capacitors, because I don't have those right now. B+ voltage still reads 19 volts when the display is lit up. Haven't tested it further.

Getting kinda nervous about this board. Even with my 40 watt iron at 2/3 setting I lifted off a foil trace on the 330uf cap and had to get creative with bridging the gap. I'll look for some 220uf caps and if I change those and there's no joy, I'm stumped unless it's a bad CCFL, then there's no point in me bothering with it.

[budm]

Re: Viewsonic VX2235WM - blank screen on/off

You may have to make a couple of these test lamps:https://www.badcaps.net/forum/showth...er+testing+cfl
Some monitor with bad lamps can run fine for hours, this one will go black after 3 hours or so, I finally took it apart to see what is going on (it runs fine with my test lamps in place all day).
http://s807.photobucket.com/user/bud...?sort=3&page=2

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

That's interesting. I'll keep that in mind.

But if it comes down to bad CCFL's, that's where I give up and scrap it, unless I can source a panel cheaply.

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

Okay, even after replacing every capacitor on this power board, I'm still getting the same problem. Monitor will run nice and dandy for a few minutes, and gives me a perfect picture, then just up and shuts off.

I'm at my wits end. Gonna try running it with a CFL unplugged, one at a time, and see what the results are.

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

Well, I think you guys are correct. It's a bad CCFL.

Starting from the bottom and working up, I unplugged one CCFL connector at a time. Having the first one unplugged, the monitor ran for about 30 seconds, unplugging the second one I got about a second before it quit.

I unplugged the third one, with the others plugged in, and now the monitor seems to be running fine. I got through a whole game of solitaire without an issue.

Now, here's where it gets really weird for me. Even with one of the CCFL's unplugged, the picture looks just fine. I figured there'd be a dark band in the image.

[budm]

Re: Viewsonic VX2235WM - blank screen on/off

It is edge lit so you will not see any dark band like you will see on LCD TV which does not use edge lit CCFL setup. The top edge and the bottom edge may not have the same brightness.
I am surprised that the circuit did not detect open lamp connection and goes into shutdown.

[Mrx3750]

Re: Viewsonic VX2235WM - blank screen on/off

I'm surprised too, but now that I'm fairly confident it's the CCFL's, how would I go about sourcing replacements, or would I be better off finding a new panel?