17" LCD Monitor - PGE 1704B/LM1704

[tmcw]

Got this monitor recently, it was non-working initially, on power-up, would get a flash from the graphics board info about no RGB signal, and the green power light on the front, flashed on and off continuously. No backlight was coming on.

Opened it up, and found 3 of the 6 Capxon's in the top right area of the powerboard bulging, so got all 6 of those replaced today, and the panel is now coming on with video signal and backlight.

There are vertical lines the whole way across the screen though, difficult to photograph, but I've attached an image anyway. Halfway across the room, you wouldn't notice them, but at working distance, they're quite evident. The lines seem to have a reddish tinge to them.

Anyway, some of the voltages off the power board aren't quite perfect, and I'm wondering if these overvoltages could be causing this issue? Here is a list of the expected voltage, (measured voltage whilst panel is on), and {measured voltage when the panel is off} (may be significant?).

24V (24.68V) {27.03}
12V (15.74V) {17.97}
5V (5.05V) {5.05}
-8V (-9.11V) {-9.49}

Any pointers as to what I need to check next?

[tom66]

Re: 17" LCD Monitor - PGE 1704B/LM1704

12V reading at 17.97V - almost 18V - looks very dodgy. What caps are there on the PSU?

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Of the 6 caps I replaced, 5 are Panasonic FMs, the other is an FC.

The 17.97V was when the monitor was connected to the power supply but off, it drops to 15.74V when the panel is switched on. Possibly still too high.

The small 7th cap on the board that I didn't replace, I understand is a startup cap, and the monitor probably wouldn't switch on if it was bad, so probably unrelated to the vertical lines issue I'm seeing?

If the diodes up around the caps were marginal, would they affect the voltages as much as I'm seeing?

[jetadm123]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Possible logic board problem. Try reseating the two ribbon cables connecting the logic board to LCD panel. Another possible problem is that the caps on the logic board have dried out. Also, check the voltage regulator(s) on the logic board to verify proper output.

[tom66]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Of the 6 caps I replaced, 5 are Panasonic FMs, the other is an FC.

The 17.97V was when the monitor was connected to the power supply but off, it drops to 15.74V when the panel is switched on. Possibly still too high.

The small 7th cap on the board that I didn't replace, I understand is a startup cap, and the monitor probably wouldn't switch on if it was bad, so probably unrelated to the vertical lines issue I'm seeing?

If the diodes up around the caps were marginal, would they affect the voltages as much as I'm seeing?

I don't think marginal diodes would cause the issue at hand.

15.74V is still too high when on. Most power supplies measure under voltage with load for example 11.5V wouldn't be unheard of and is usually completely fine.

What voltage caps did you install?

If you installed 16V ones, they are probably toasty, and going to fail.

Even if you installed 25V or 35V ones, who knows what ripple the PSU has due to other faults? Maybe your multimeter is averaging it and the rail has spikes in the 25-30V range. I've seen it happen before!

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Ok, reseated the ribbon cables, no difference.

I've attached a photo of the logic board. The voltage regulators are usually given the "U..." designation, correct? I can see 3 components marked "U", circled in the photo.

The first 2 (from the left) although slightly different numbers, one has 1117-33, and the other has LD1117.

The first one: Input: 5.05v; Output: 3.3v
The second one: Input: 3.28v; Output: 1.8v

The 3rd one has the numbers "431" on it. I'm not sure what the relevant document is, but the voltages I'm seeing are 2.47v and 13.7v on the left and right (if this document is correct, then the voltages above are on pins 1 and 2 respectively on the SOT-23-3 package).

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

I don't think marginal diodes would cause the issue at hand.

15.74V is still too high when on. Most power supplies measure under voltage with load for example 11.5V wouldn't be unheard of and is usually completely fine.

What voltage caps did you install?

If you installed 16V ones, they are probably toasty, and going to fail.

Even if you installed 25V or 35V ones, who knows what ripple the PSU has due to other faults? Maybe your multimeter is averaging it and the rail has spikes in the 25-30V range. I've seen it happen before!

I used the same voltage as were on originally. From left to right in the picture, 2x50V, 1x25V and 3x16V.

Not sure what my multimeter does, it's an old HP E2377A.

I have an oscilliscope, can I use it to check for spikes?

[jetadm123]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Ok, reseated the ribbon cables, no difference.

I've attached a photo of the logic board. The voltage regulators are usually given the "U..." designation, correct? I can see 3 components marked "U", circled in the photo.

The first 2 (from the left) although slightly different numbers, one has 1117-33, and the other has LD1117.

The first one: Input: 5.05v; Output: 3.3v
The second one: Input: 3.28v; Output: 1.8v

The 3rd one has the numbers "431" on it. I'm not sure what the relevant document is, but the voltages I'm seeing are 2.47v and 13.7v on the left and right (if this document is correct, then the voltages above are on pins 1 and 2 respectively on the SOT-23-3 package).

The first two regulators have good output. The third one does not look like a regulator.

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

The first two regulators have good output. The third one does not look like a regulator.

Thanks for confirming, I was thinking that was the case for the first 2.

Ive attached another closeup of the third circled component, definitely marked U8.

One thing I noticed is that when the PC went into power saving mode, it switched off the monitor, and the 13.7V on this U8 dropped to zero.

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Also, I took out the oscilliscope, and probed the voltage outputs from the power board, and the resulting voltages didn't seem any noisier than when there is no voltage being probed.

[tom66]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Also, I took out the oscilliscope, and probed the voltage outputs from the power board, and the resulting voltages didn't seem any noisier than when there is no voltage being probed.

Did you use AC coupling? Set V/div down to a low scale, 50mV/div or so. Ripple should not exceed one division either way.

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Unfortunately, I haven't spent much time yet getting to know the scope. I did put the divisions down to about 200mV before I began to see spikes, but I'm really not that clued into how to use it yet with circuits, so what I was doing may be meaningless. I've only played with it with a signal generator as of yet. Need to find some good tutorials, and some time!

On a side note, I left the monitor switched on for about 45 minutes (no power saving), and the caps weren't hot at all. The cap nearest the transformer did get a little warm, but it wasn't so hot that it became uncomfortable to hold.

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Ok, I changed a few of the caps on the logic board, but the vertical lines are still present. I changed the one in the top left corner, and the two over in the top right, as all 3 appear to be on the 12V line (which is actually 13.07V as it goes across the ribbon to the panel board (what is the correct name for this board, is it the Tcon board?).

The brightness range seems to be much better though.

The other caps seem to be involved in the 5V line, which seems to be ok, and the sound in/out area which is ok too, so I haven't changed any of those.

I can't seem to trace the 24V line, it goes towards the top of the board from the connector, but seems to disappear under one of the ribbon connectors. I can see a 20.50V on one of the ribbon lines, so presume it comes from the 24V line somewhere.

The number on this board is MB-R2523B-DTD, which seems to be used in other monitors, but I can't find a schematic.

I've attached 3 photos of the monitor to show the lines. When looking at an angle from the bottom, the lines are very evident; straight on, the lines are sometimes there, sometimes not, depends on the background; and looking at an angle from the top, the lines almost disappear completely.

Also, if I go into the menu, and change the screen position, either horizontally or vertically, the lines don't move with the picture, they remain in the same position.

Moving the ribbon cables or pressing at the area where the panel board is connected to the panel doesn't alter the picture in the slightest.

These symptoms may give someone an idea what might be wrong.

I also had a look at the voltages going across the ribbon cable, and was mainly seeing voltages around the 1.2-1.8 range. Also saw a couple of 3.3Vs, a -5V and the 20.5V, but I guess without schematics, not much point measuring these.

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Another thing which may be significant is that when the monitor OSD is invoked, the lines do not go through the OSD.

There are lines above and below the OSD, but the OSD is crystal clear.

[joshnz]

Re: 17" LCD Monitor - PGE 1704B/LM1704

How are you getting signal to the monitor DVI or VGA?

[tom66]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Also, if I go into the menu, and change the screen position, either horizontally or vertically, the lines don't move with the picture, they remain in the same position.

This tells us the problem is either with the TCON or VGA/DVI input.

Does the monitor have a second input you can try?

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

VGA

There looks like there is space for DVI in another revision, but there is no DVI connector, and lots of unpopulated spaces for associated surface-mount caps and resistors.

EDIT - no second input, just VGA. Also, have ruled out the cable, and have tried another computer, but the issue remains.

[tmcw]

Re: 17" LCD Monitor - PGE 1704B/LM1704

This tells us the problem is either with the TCON or VGA/DVI input.

Does the monitor have a second input you can try?

If the TCON was bad, would/could I still see a crystal clear OSD?

[joshnz]

Re: 17" LCD Monitor - PGE 1704B/LM1704

Hmmm I was thinking interference in the input signal from vga so maybe.
When i was running a monitor near a pc with the side off my display would go weird/distorted and lots of other things now i use DVI no problems with interference sad you don't have DVI so hard to isolate that as a possible cause.

[tom66]

Re: 17" LCD Monitor - PGE 1704B/LM1704

If the TCON was bad, would/could I still see a crystal clear OSD?

Ah - didn't catch that. In which case problem with VGA/DVI input, again try a second input if possible, for example if using DVI try the VGA input, or otherwise.