Samsung 930b LCD cold start problem (inverter?)

[gdement]

Re: Samsung 930b LCD cold start problem (inverter?)

Interesting if it's sync on green capable, because if anything I've found this monitor very picky about input signals.

I have a couple old (~1996 or so) Diamond brand PCI video cards I sometimes use when testing motherboards, and this monitor hates both of them. It usually works okay in higher modes like a Windows GUI, but it blanks out sporadically in lower modes, including the POST and BIOS setup screens. The video just disappears at random intervals - it's extremely annoying.

[Wizard]

Re: Samsung 930b LCD cold start problem (inverter?)

930B any of these vintage with "B" is sync on green capable.

Good save and it is one of these monitors Pentium should look for especially for his oddball computers that uses sync on green signal.

Cheers, Wizard

[gdement]

Re: Samsung 930b LCD cold start problem (inverter?)

Fixed.

Seems the LCD screen is sealed off from everything else, so no problem with dirt since I didn't need to go in there.

The last time this screen ended up cold, I couldn't get it to run anymore, even with a lamp heating it from the back. I ended up melting the plastic trying to heat it up enough to work.
===

With great care and lots of photos, I got it apart. The video input board didn't look have much to look at. <photo attached at bottom>

Over to the power board, and to my relief I found a bulged Samxon GF cap. Good, should be easy to fix.
Turns out all the caps are made by Samxon, including the large 100uF 450v input cap and a small 47uF cap (which I didn't notice until looking at the pictures just now).


The originals caps were:
2x Samxon GF 1000uF 16V 10x20
2x Samxon GF 1000uF 25V 10x20
1x Samxon GF 470uF 25v 10xwhatever
1x Samxon KM 100uF 450v 18x ~36 (replaced with 18x40)
1x Samxon ?? 47uF ??v.

I ordered replacements from digikey for all but the 47uF, which I overlooked. The Samxon GF has the same ESR specs as Chemicon KY, and same standard case sizes. KY is also a high endurance cap, so it seemed perfect.
Unfortunately, the 1000uF 25V GF's must have been a custom size, because they aren't listed in 10x20 as standard (for either series). I had to order the KY's in 12.5x20 in order to maintain vertical clearance. 10x30 is too tall.

All replacements are KY series except the large input cap, which is a Chemicon KXG.


New caps installed:

Had to tilt things just slightly to get the 12.5mm caps in there, but as expected it wasn't much of a problem.

Put it back together and I got a flat white screen.

Damn. Well at least the power is on.

Took it back apart, turns out this flimsy little video connector wasn't quite latched in right. I had fiddled with it before deciding it didn't need to be unplugged. Photo shows it in proper position, before I had messed it up:

The metal hooks were unlatched and it was bending to one side a bit. I got it clamped back down, but it sure doesn't seem like a very solid connection.

Anyway, it works now.


See attached photos for an overhead of the power board (if anybody cares). I also have a big photo of the back side of the PCB, but I didn't upload it because it's big, and shrinking it would make it useless. If somebody wants to see the trace layout I'll post it.

[davmax]

Re: Samsung 930b LCD cold start problem (inverter?)

Intrems of getting apart look at the videos that can be accessed from this page: http://www.lcdrepair.us/powersupply.html

[gdement]

I have a Samsung SyncMaster 930b LCD. I think the "b" just means it's black, so 930 is probably sufficient.

Starting about a week ago, I noticed that when I turn on the monitor, the backlight stays dark and the green power LED starts blinking rapidly. The speed of the blinking LED is faster than what I'd see if there was simply no input signal. It blinks about twice per second, and only spends a split moment in the ON condition - most of the time the LED is off. If I were to guess, it looks more like power cycling rather than an intentional blink.
The monitor refuses to turn off when it's doing this - it's stuck trying to power up the backlight unless I unplug it.

After blinking the LED for several seconds the backlight eventually turned on. As long as I leave the backlight on (power management disabled), then there are no further problems. If I turn it off but turn it back on immediately, it works fine. It's only a problem when it's cold.

I haven't noticed if the screen is working when the backlight is off.


This problem has gradually gotten worse each day, taking slightly longer to power up each time.

Since I started leaving the monitor on constantly, I changed the brightness of my backlight to a much lower setting. Then I absent mindedly turned it off.
Next time I tried to start it, the cold start problem was much worse, but I don't know if the low brightness setting is just a coincidence.

I left it blinking for hours and the backlight never came on. Then I propped a lamp up against it and let the bulb heat up the back of the monitor. After doing that, I came back about an hour later and found the monitor working.

===============


Am I correct in assuming this is an inverter problem? How easily do these monitors typically come apart? Can I get to the inverter without disassembling anything else? I really don't want to get dirt into it or have to touch the LCD portion at all, if I can help it.

For now, I'm just going to leave it on, but someday it will end up turned off again so I might as well find out what I'm up against. Never opened an LCD before and the thought worries me. I suppose it might still be under warranty but I can't find any documentation or packaging whatsoever.