Viewsonic VG191b

[Lakerat]

Hi,

I'm new here with very limited electronic exp. (electronic techs help me out at work).

I picked up this veiwsonic from the curb. Power light stays on but no screen at all. I opened it up and everything looks good. The power supply is on the power cord. No bulging caps at all.
Any ideas on where to start with this one?

Thanks

[retiredcaps]

Re: Viewsonic VG191b

I'm new here with very limited electronic exp. (electronic techs help me out at work).

When you turn on the LCD, do you see the backlight flash on briefly? Or is it just black?

The answer matters because it tells us which direction to look for problems.

Post clear focused pictures AFTER reading

https://www.badcaps.net/forum/showthread.php?t=1868

Please do not post pictures inline.

Take your boards to a window on a sunny day, turn flash off, and use macro mode. Take a top down view of all your boards (front and back). Make sure the photo is legible so that we can read the PCB printing clearly. A shutter speed of 1/125 or faster will produce nice clear focus pictures. Try to get a photo that is 2000x2000 resolution or as close as possible.

Here is an example of the pictures we want.

https://www.badcaps.net/forum/showpos...94&postcount=1

[Lakerat]

Re: Viewsonic VG191b

No flash on screen at all ..All black have not tried looking at screen with bright lite.

Will try to get some photo's soon getting late here.

[Rtech]

Re: Viewsonic VG191b

I assume that,'the power supply being on the power cord',means its an external adaptor ??If that is the case,and as requested by retired Caps, you take some photos,ensure very clear ones are taken of the Inverter board(this is usually rectangular, smallish,and the Screen lamps plug into it.

[Lakerat]

Re: Viewsonic VG191b

The power supply is external, The inveter board is a long narrow rectangle.
Is there a reset function for this viewsonic?
Any way to check the bulbs.?

I will try to post pics tommorow night.

[retiredcaps]

Re: Viewsonic VG191b

The inveter board is a long narrow rectangle.

If I'm thinking like Rtech, I suspect you may have a blown fuse or a shorted transistor on the inverter board.

Thus, you will need a multimeter to test.

[Lakerat]

Re: Viewsonic VG191b

I
I have found what looks like a small fuse on inverter board marked (yellow in color) F1 does not test good what should I use in place of this or for testing ? would a minature glass fuse work?

[retiredcaps]

Re: Viewsonic VG191b

I
I have found what looks like a small fuse on inverter board marked (yellow in color) F1 does not test good what should I use in place of this or for testing ? would a minature glass fuse work?

Pictures? Pictures!!!

What does this fuse look like?

Fuses may go bad by themselves. OR some other component is drawing too much current and causing the fuse to blow.

Replacing the fuse without testing other components like transistors or FETs for shorts is likely to blow the fuse.

[Lakerat]

Re: Viewsonic VG191b

Sorry I can't get photos until tomorrow night. Fuse is soldered on and is a mustard color. will try my best to look at this board with a ohm meter....but first I will try to look inside power supply that is on the power cord

[Rtech]

Re: Viewsonic VG191b

If the Power light comes on , then the Power Supply should be fine,and would not try and open that.The logical main culprit is the Inverter Board, as it is in the majority of monitors which have an external PSU,with a fault sympton like this.

[Lakerat]

Re: Viewsonic VG191b

I know pictures will get them here tonight !! (I'm away from home M-F and camera is at my home)
I need a layout or schematic of the inveter board
T651008.00
I checked for the layout and found all others for this monitor but not for this board any help?
Thanks

[Lakerat]

Re: Viewsonic VG191b

Here is my photos of the board...sorry so dark

[Rtech]

Re: Viewsonic VG191b

It would simplfy the process if you had a spare good backlight ?????.The other things to try should you not have one,is to compare the resistance readings,using a 2000 ohm scale if possible, on the output pins of the two transformers.The Output pins being the ones closest to the ends of the board.Also the two capacitors behind the connector may be faulty,and of course your failed fuse.

[Lakerat]

Re: Viewsonic VG191b

Ok here is what I tried... made a jumper for fuse (testing only) now when I turn it on I see the screen show Image of whats on computer for about 3-4 seconds then goes out what should I look for here?

[retiredcaps]

Re: Viewsonic VG191b

Ok here is what I tried... made a jumper for fuse (testing only) now when I turn it on I see the screen show Image of whats on computer for about 3-4 seconds then goes out what should I look for here?

Rtech makes good suggestions in post #13. More detailed instructions are in points #4 and #5 at

https://www.badcaps.net/forum/showthread.php?t=10419

[Lakerat]

Re: Viewsonic VG191b

I have changed the small caps on inverter board not I can see both lights flash for a split second on to and bottom of screen....Since this has a external power supply and it plugs into other board and it is loaded with the crap X caps would could that be something to look at? power light stays on and for a few seconds I can see a image when power is turned on. I put a ohm meter at both transformers and got the same readings.

[retiredcaps]

Re: Viewsonic VG191b

I have changed the small caps on inverter board not I can see both lights flash for a split second on to and bottom of screen....Since this has a external power supply and it plugs into other board and it is loaded with the crap X caps would could that be something to look at? power light stays on and for a few seconds I can see a image when power is turned on. I put a ohm meter at both transformers and got the same readings.

If you have an external PS, we are going to assume it is okay for now, because you get the backlights to flash on.

If the inverter transformers test okay and you see the backlights flash on for a second, then try testing the ccfl tubes to rule out a bad ccfl or ccfls.

[Lakerat]

Re: Viewsonic VG191b

I did a check on voltage on main board where ribbon goes to inverter board

#1 12 #2 12 #3 12 #4 0 #5 0 #6 1 #7 5.1 #8 0 I did these with neg side of meter using case for ground . I have one more monitor but ends are different on wires for bulbs. I read somewhere that you can use a computer case light to check black light bulbs. will this work?

[retiredcaps]

Re: Viewsonic VG191b

I did a check on voltage on main board where ribbon goes to inverter board

#1 12 #2 12 #3 12 #4 0 #5 0 #6 1 #7 5.1 #8 0 I did these with neg side of meter using case for ground . I have one more monitor but ends are different on wires for bulbs. I read somewhere that you can use a computer case light to check black light bulbs. will this work?

Those voltages look like what I would expect from an external PS (assuming it is 12V DC). The 5.1 is pretty standard for use with the logic board.

I don't have any experience with the computer case light so I don't know if it will work or not.

[Rtech]

Re: Viewsonic VG191b

Inverter PCB's are normally very difficult to fault find,if you eliminate the standard type faults,and so eliminating the CCFL's is really a prerequisite,and,like retiredcaps I have never used a Computer case lamp in this situation.The only other things you can try are resoldering of all the transformer pins,AND there are usually two 'coils' sitting on the board,and over time they can become dry jointed..so thats worth a try as well.