Princeton VL1919

[megabyt]

A friend gave me a brand new monitor (5 years old but never removed from the original box). It worked fine for 1 day and then the next day the blue power light comes on briefly then a white screen. I have repaired the same model recently that had bad capacitors and that went well. The capacitors appear to be OK on this one and I see posts suggesting that a fuse might be bad. I have checked the fuses I have been able to identify but they all show continuity. I have attached pictures of both boards involved to see if someone else can direct me to a component that I may have missed. Thanks.

[Nocta]

Re: Princeton VL1919

Everytime I got a white screen, problem was the ribbon cable, it was connected in the other way.

Caps may look OK but they can die from heat and age too.

It'd be better if you check the fuse using resistance instead of continuity. A good fuse should read 1 ohm or less.

[retiredcaps]

Re: Princeton VL1919

The "panel" board which is located at the top of the lcd and may be underneath a metal shield usually has a SMD fuse which might be blown.

Follow the multicolored cable from the main board and that should lead you to the "panel" board.

[megabyt]

Re: Princeton VL1919

Hi,

I have attached photos of the panel board. I am new to the forum and the pictures are the best that my camera can do. I noticed an F5 near the connector but it tested good. Hate to take a basically brand new monitor to the recycle drop off but it is not looking good. Is it possible that bad capacitors could give the same white screen issue? As mentioned the monitor has been in a box for 6 years unused so not much else could "wear out" except from age.

Thanks for the help.

[retiredcaps]

Re: Princeton VL1919

U3 on the main board is a voltage regulator. So is U1 on the panel board.

To test a voltage regulator,

1) Set your multimeter (if manual range) to 20V DC.

2) Put your black probe on a ground screw. Leave it there the entire time. This is your ground.

3) Put your red probe on each of the pins including the "cut" pin, but ignore the "fat" tab. The fat tab is "up" or "north". Number the pins left to right.

4) You should have 3 readings per regulator.

5) Report them like so along with the part number (include all lines on the IC) of the IC.

U100
AS1117-33
pin 1 = 0.0
pin 2 = 3.3
pin 3 = 5.0

[megabyt]

Re: Princeton VL1919

Per your request:

U3 is marked 6F8L 1117L
1 = 2.5
2 = 4.5
3 = 5.0

U1 is marked MM1117 A B632
1 = 0.0
2 = 0.0
3 = 0.0

Thanks for the help.

[retiredcaps]

Re: Princeton VL1919

Per your request:

U3 is marked 6F8L 1117L
1 = 2.5
2 = 4.5
3 = 5.0

U1 is marked MM1117 A B632
1 = 0.0
2 = 0.0
3 = 0.0

Thanks for the help.

Since this has happened to me 3 times in the last week, I will ask you to verify both those readings above before I go into the explanation why they are bad. 3 people have posted incorrect readings or measured them wrong.

[megabyt]

Re: Princeton VL1919

Hi,
I have attached a photo of my boards annotated with text boxes to show where the voltage was measured. I used a digital meter this time to get more accurate readings. Hope this helps you help me!

Thanks

[selldoor]

Re: Princeton VL1919

On the panel board what voltage do you get on each side of fuse.
There are also voltage check points labelled 5V1 just beside the fuse and
V33 beside the voltage regulator - Meter on 20VDC black probe on ground screw
check those points. If nothing take the connecting cable out clean it reseat and
try again

[megabyt]

Re: Princeton VL1919

I think we are getting somewhere. I just realized that the screen (face down so I couldn't see it) had been going black after 30 seconds or so. When this is the case I get zero voltage. If I test the voltage point when screen is still lighted, it shows 5 volts and the south side of the fuse shows the same but the north side shows zero so it looks like a fuse issue. The regulator still shows zero voltage on all tabs but that is presumably because of the blown fuse? I pulled the power and tested continuity between the voltage point and the south end of the fuse and that is good. Between the voltage point and the north end of the fuse the circuit is open. So I have a bad fuse and can probably change it myself BUT the burning question is why did the fuse blow I guess?

I did get continuity on that same fuse when I first posted however so that is a mystery but maybe just didn't push hard enough on the probes.

Thanks