Today i have cleaned my junkpile, and i found this nice 19" crt from Medion. It is not mutch used, but there is an anoying problem.
If the crt is on for about a half to one hour the picture goes off, but the green power LED is still on. After several hours w/o power it is working again.
It is the same if i suspend the monitor, it dosn`t switch to the stand by or suspend mode, instead the green power LED remains green. It is the same if the pc is off, a normal CRT should went in to suspend mode and the LED should turne yellow, but if the failure occure, this crt don`t do that.
After resoldering all the mechanically or by temperature stressed solder joints, wich fixed for me several Medion CRT`s there was no succes. I replaced some suspected caps, but with no succes again.
I discovered, that there is an relay, near the input rectifier bridge. If the failure occurs, this relay don`t switch on. But it dosn't help to switch this relay on by hand (i.e. shorting the PNP driver transistors base to ground).
If the crt is bared, the occurance of the problem is reduced.
The main SMPS is working, and the High voltage section is working too.
For me it seems that there is somwehere an badcap on the s/b controler section, but i duno wich controler does handle it. There are about 3 chips, the main SMPS controler, a Daewoo uControler wich controls the mentioned relay, but the caps there seems to be ok.And then there is an Atmel uControler near the front pannel, assuming that this is responsible for OSD.
Up to now i will try to replace severall 10uF HEC caps near the Deawhoo uControler, but this is only the last effort. The whole crt is full of badcaps like HEC, Elite etc.
This crt is not bad otherwiese, thus i hesistate to trash em, as it is obviousely< not realy damaged....
If anyone hafe suggestion where to look it would be apreciated.
The power consumption in failure mode is about 70w, so i assume that all major systems are working.
If the crt is on for about a half to one hour the picture goes off, but the green power LED is still on. After several hours w/o power it is working again.
It is the same if i suspend the monitor, it dosn`t switch to the stand by or suspend mode, instead the green power LED remains green. It is the same if the pc is off, a normal CRT should went in to suspend mode and the LED should turne yellow, but if the failure occure, this crt don`t do that.
After resoldering all the mechanically or by temperature stressed solder joints, wich fixed for me several Medion CRT`s there was no succes. I replaced some suspected caps, but with no succes again.
I discovered, that there is an relay, near the input rectifier bridge. If the failure occurs, this relay don`t switch on. But it dosn't help to switch this relay on by hand (i.e. shorting the PNP driver transistors base to ground).
If the crt is bared, the occurance of the problem is reduced.
The main SMPS is working, and the High voltage section is working too.
For me it seems that there is somwehere an badcap on the s/b controler section, but i duno wich controler does handle it. There are about 3 chips, the main SMPS controler, a Daewoo uControler wich controls the mentioned relay, but the caps there seems to be ok.And then there is an Atmel uControler near the front pannel, assuming that this is responsible for OSD.
Up to now i will try to replace severall 10uF HEC caps near the Deawhoo uControler, but this is only the last effort. The whole crt is full of badcaps like HEC, Elite etc.
This crt is not bad otherwiese, thus i hesistate to trash em, as it is obviousely< not realy damaged....
If anyone hafe suggestion where to look it would be apreciated.
The power consumption in failure mode is about 70w, so i assume that all major systems are working.
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