Makvision M2929 dark picture

[lilshawn]

Mackvision M2929D1G-62 monitor from a big buck safari game.

picture from the computer is dark and barely seen on the screen. video signal good, verified by several sources.

pressing the button to bring up the OSD shows the OSD nice and bright with all the proper colors.



pulled up the service menu and checked the settings in there...all good. maxed out the brightness and contrast to see the video image. still dark.

OSD has seperate input to video amp, but same drive circuit so the color drive is good, transistors are good, high voltage is good then. It's just the video signal.

replaced the capacitors in line for the RGB (10uF 25v) checked the diodes and resistors (all within spec) some kind of 5V regulator biasing the signal?? 5 volt regulator is good. video amp issue then?

ordered and replaced LM1269NA video amp chip. no change.

what gives? Why would the OSD display perfectly bright video but the video from the computer be super dark?

[lilshawn]

finally got a response out of suzo happ. called, left messages and emailed. got a response today via email...

ABL voltage too low
Bad diode on chassis D21
Replace use 1N4937


eeeeeeeeegggghhhh I don't know about that....I would assume the ABL would also affect the menu image as well, but at this point it's worth a shot. off to the parts store.

[lilshawn]

huh, well what do ya know. I haven't the foggiest why the ABL does not affect the OSD input but it doesn't. replacing the diode D21 fixed the issue.

I was unable to quickly source a 1N4937, but the original Diode was a 1N4148 which I have an abundance of. replacing the diode with the 4148 fixed the issue. I have some 4937's on order and i'll swap it out once they show up.

weird issue has a weird fix. 

[qrz]

OSD is direct to the cathode drivers for that very reason .

can't access the service menu if unable to see it   

[lilshawn]

OSD is direct to the cathode drivers for that very reason .

can't access the service menu if unable to see it   

which is weird because it doesn't. The OSD feeds directly into the video amp (it's own set of inputs) same as the VGA from the computer. a line to the video amp pulled up activates the OSD input. That's why I concentrated my diagnostics to that section upstream from the amp.

After looking more into it, seems when the OSD is active, the video amp "deactivates" the ABL during the small portion the OSD is occupying which is why the OSD shows up fine. the ABL normally shunts through the (defective) diode to ground, when the OSD needs to be displayed, the ABL line from the video amp is activated, the ABL is rerouted back through the video amp and the ABL level is modified. when the section of scanline for the OSD is finished the alternative route the ABL is taking is "cut" and the ABL shunts through the diode to ground again.

Lurning, sumtimes i dew it. 

[grantspain]

nice one for suzo happ giving you the information to actual fix for this,most distributors would say send it in for repair-and then charge you the price of a chassis for the repair

[Dawgz Rule]

nice one for suzo happ giving you the information to actual fix for this,most distributors would say send it in for repair-and then charge you the price of a chassis for the repair

Suzo Happ tech support is pretty good with this kind of stuff.   They have some crusty old guy there that has been doing CRT repairs for years and years.  I have spoken to him a couple of times and he is a wealth of knowledge.

[Dough]

Well it was 5 years in the making, but I just had this problem in the Makvision M2929 in my buck safari, and your tip got me back up and running in one day.  Thanks!

[lilshawn]

 

noice!

[lilshawn]

Just had another 2929 monitor come in to the shop... exact same problem... exact same fix. 

Glad I remembered about this.

If you got one of these, probably a good idea to swap it with the 1N4937.