Hi,
Can anyone identify the cause of the following symptoms?
Someone suggested I replace the lower Y-buffer but I am interested if there are any other qualified assessments? Have scratched round on the web for a few days and cannot find any other instances of this exact behaviour.
Initially picture is fine, then some slight blackness appears in the lower 2/5ths of screen after about 4 minutes. As the set 'warms up' this gets worse until it is almost completely black but occasionally flashes through the picture if the frame is bright. The image is still there, just hard to see or overlain with a ghost image.
Photo's below.. progress from no problem to almost complete blackout after 15 minutes.
Often then it clears up for a few minutes than then the ghosting/rolling effect starts on the bottom of the screen only
Example with screen set to full white raster..
First off I checked and fine tuned all voltages ( VS, VA, -Vy, VSC, VZB) which had minor deviations of a volt or two.
I dont have an oscilloscope so cannot check waveform.
I completely removed the lower board Y-drive board (physically) including all ribbon and TCP cables and ran the set for a minute. This was the result:
Checked the heat of the Ysus board as the issue seems to be heat related.
One of these heatsinks gets astonishingly hot (see photo). But maybe that is normal?
Checked the back of the board, no evidence of bad solder joints due to heat, touched up the transistor legs to be sure. Inspected all other components with magnifying glass, no obvious damage.
At the bottom of the rightmost heatsink is a mosfet? which I suspect is the source of most of the heat on that heatsink as the board is much browner around it's legs than the other transistors along the line which are of a different type.
The chip is stamped as K8A60DA 1:8
I only have a 30w soldering iron, so I know it would be nigh impossible to get that line of chips on the heatsink out for testing.
There is a chance I could get it off the heatsink in-situ and then de solder it, but will only attempt this if this sort of chip has a high probability of causing the effect I described.
Apart from that the only observation I can make is a buzzing from the ysus board that corresponds to the lower half flickering but I guess that is only to be expected as signal frequency cuts in and out?
Put is all back together and it is back to it's old behaviour - after a couple of minutes the bottom 2/5ths start flickering and it gets darker/worse with occasional brief flickers of clarity.
I tried running a fan blowing cool air over the various components/boards to see if there was any effect of cooling on the symptom.
To my surprise cooling components with air did not appear to have any effect so now I am starting to doubt whether it is heat related even though the problem only starts after 5 minutes or so.
Starts off with an increasing darker section on the bottom of the screen, eventually it goes almost completely black, then after a few minutes is lightens up again but then there is this ghosting/duplication problem as demonstrated in this video - this is the second phase and more permanent problem once the set has been running for 20 minutes or so.
---- >>> View My Video <<< ---
i still have no idea which board is the culprit.
Can anyone identify the cause of the following symptoms?
Someone suggested I replace the lower Y-buffer but I am interested if there are any other qualified assessments? Have scratched round on the web for a few days and cannot find any other instances of this exact behaviour.
Initially picture is fine, then some slight blackness appears in the lower 2/5ths of screen after about 4 minutes. As the set 'warms up' this gets worse until it is almost completely black but occasionally flashes through the picture if the frame is bright. The image is still there, just hard to see or overlain with a ghost image.
Photo's below.. progress from no problem to almost complete blackout after 15 minutes.
Often then it clears up for a few minutes than then the ghosting/rolling effect starts on the bottom of the screen only
Example with screen set to full white raster..
First off I checked and fine tuned all voltages ( VS, VA, -Vy, VSC, VZB) which had minor deviations of a volt or two.
I dont have an oscilloscope so cannot check waveform.
I completely removed the lower board Y-drive board (physically) including all ribbon and TCP cables and ran the set for a minute. This was the result:
Checked the heat of the Ysus board as the issue seems to be heat related.
One of these heatsinks gets astonishingly hot (see photo). But maybe that is normal?
Checked the back of the board, no evidence of bad solder joints due to heat, touched up the transistor legs to be sure. Inspected all other components with magnifying glass, no obvious damage.
At the bottom of the rightmost heatsink is a mosfet? which I suspect is the source of most of the heat on that heatsink as the board is much browner around it's legs than the other transistors along the line which are of a different type.
The chip is stamped as K8A60DA 1:8
I only have a 30w soldering iron, so I know it would be nigh impossible to get that line of chips on the heatsink out for testing.
There is a chance I could get it off the heatsink in-situ and then de solder it, but will only attempt this if this sort of chip has a high probability of causing the effect I described.
Apart from that the only observation I can make is a buzzing from the ysus board that corresponds to the lower half flickering but I guess that is only to be expected as signal frequency cuts in and out?
Put is all back together and it is back to it's old behaviour - after a couple of minutes the bottom 2/5ths start flickering and it gets darker/worse with occasional brief flickers of clarity.
I tried running a fan blowing cool air over the various components/boards to see if there was any effect of cooling on the symptom.
To my surprise cooling components with air did not appear to have any effect so now I am starting to doubt whether it is heat related even though the problem only starts after 5 minutes or so.
Starts off with an increasing darker section on the bottom of the screen, eventually it goes almost completely black, then after a few minutes is lightens up again but then there is this ghosting/duplication problem as demonstrated in this video - this is the second phase and more permanent problem once the set has been running for 20 minutes or so.
---- >>> View My Video <<< ---
i still have no idea which board is the culprit.
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