Sun (Sony?) GDM-5410 Excessive brightness

brightness/contrast.

Sony's,

From what I've read this is a pretty common problem -- read more here:

Hope that helps!

That's the exact site I used to fix one a couple of months ago. That WILL fix you up, great unit to keep. The problem is in getting the right resistance to give you a good level. Sky.

Does anyone know why this problem happens? CRTs don't normally increase in brightness as they age. Andy Cuffe

snipped-for-privacy@psu.edu

Something must drift in the circuitry, my Sony G520 is on the verge of being too bright, with the user brightness control turned all the way down and I've seen others that were worse.

Hi,

"JM" wrote

Thanks for the pointer but the "fix" appears to be just a bandaid -- it doesn't identify the actual *failure*... just patches things to limp along.

A quick peek at the schematic seems to suggest the contrast regulator may be wimping out (beta degradation?). I'll try to make some time to pull the skin off it this weekend and see what things look like. Maybe a $5 repair (instead of the 10c workaround). Worth the extra money, IMO! :>

Thanks!

--don

If that's the case, it would be nice to find what's drifting and replace it instead of making other modifications. The resistors in the G2 circuit are not off value. Andy Cuffe

snipped-for-privacy@psu.edu

It is not a matter of what is drifting on the Sony monitors.

The use I2C control for the G2 voltage. If either the video process ic that also does the G2 fails (which it does) or the eeprom gets corrupted or fails (which they do), there is no way to actually troubleshoot and fix it without the Sony DAS alignment software for the unit.

With the alignment software it is possible to find out what the G2 value is in the eeprom and see if it can be changed. If it can be changed then you know the failure is in the CXA video ic.

The usual failure mode is the eeprom will fail completely. Totally black picture due to no G2 voltage. Eeprom will become corrupt, either full G2 voltage or no G2 voltage. Video ic will fail, OSD will be ok, almost always full G2 voltage and over bright.

The design and high failure basically requires that you are a Sony authorized servicer for these in order to see enough of them to warrant the cost of all the different alignment jigs and software versions for each monitor line.

Forgot to add one thing. The auto adjust looks at the AKB return from the guns. We are all aware of how well Sony specs out the AKB circuit to determine when the picture tube is beyond tolerance.

So if the tube is beyond what Sony considers acceptable specification, the auto adjust will not work and you may wind up with all bright or all dark picture. Basically not useable.

The problem I'm talking about is a gradual increase in brightness over a long period of time. Eventually, even at minimum brightness, black is no longer black. Reducing the G2 voltage, either through DAS, or a resistor change restores normal operation. I'm just wondering what is actually drifting. Is the G2 going too high? Is something in the video circuit drifting? Is the CRT changing in some way?

The auto adjust in a lot of the 21" monitors won't fix it for some reason. They seem to have fixed this in the next generation of 21" monitors which respond well to running auto adjust. The 19" ones can always be fixed by running auto adjust. I've seen ones that were so bright the background had retrace lines, but auto adjust brought everything back to normal. Andy Cuffe

snipped-for-privacy@psu.edu

That would be the picture tube causing the problem then.

The G2 is directly controlled by the AKB as well as the base value of the eeprom.

I am assuming that in later versions they reduced the amount the AKB affected the G2 voltage.

As always make sure the standard stuff is good, video output power supply voltage that could be low due to a weak or high esr capacitor, etc.