My set has been acting up for many months now. The symptom is that the screen randomly goes black and then returns to normal several seconds later. Sometimes it goes black for a few seconds longer and then shows the Samsung startup splash screen before the program returns to the display. The issue is quite variable: sometimes it can go many tens of hours without going black; other times, it will do it 5 times in 15 minutes. The problem occurs with HDMI inputs (any port) and component video. I haven't tested composite or antenna. When using HDMI, the TV is downstream from my audio receiver/HDMI select so the sound behavior is not helpful in diagnosis.
All voltages are nominal, including Vs and Va as well as the 15V and standby and main 5V supplies.
Because it is such an intermittent problem, I devised a circuit to help isolate the issue between the main board and the power supply. Using an octal darlington driver, the circuit buffers and displays the state of the A5V (stdby), PS_ON, and VS_ON signals on LEDs. The PS_ON and VS_ON circuits include an R-C circuit to stretch out brief dropouts to aid in detection. The circuit has shown me that when the screen blanks, both the PS_ON and VS_ON go to their off states (3.3V and 0V, respectively) for the duration of the outage and seem to come back up with about the same relative timing as when powering up the set from scratch. The standby 5V remains steadily on. On occasions when the Samsung logo appears before recovering, the behavior is the same, just a little longer in duration.
This leads me to believe that the problem is in the main board. I am assuming it is supposed to hold PS_ON low when the set is on and also that VS_ON is slaved to PS_ON (either on the PS or logic boards, as it does not seem to connect to the main board). So my first question is: do you agree with my diagnosis that it's the main board?
Assuming the problem is on the main board, ideally, I'd repair the main board or have it repaired, but replacing is acceptable, too. I'm afraid that the intermittent nature of the problem will make it hard to pin down to a component. Are there any signals on the board I could similarly instrument to isolate further? I don't have a scope available, unfortunately, but can cobble together a circuit to monitor a relevant signal.
I see that the EEPROM is a common failure point in Samsung plasmas, but all the examples I've found in the forum fail hard immediately following power on, rather than being intermittent during steady viewing. Is the EEPROM actively accessed during steady-state operation or only at power-up and during state changes? If it is actively read or written in steady-state operation, I might attempt to replace it. I do have a brand new hot air soldering tool, the purchase of which I still need to justify. ;-)
Can anyone suggest other paths to pursue? I look forward to the community's suggestions.
All voltages are nominal, including Vs and Va as well as the 15V and standby and main 5V supplies.
Because it is such an intermittent problem, I devised a circuit to help isolate the issue between the main board and the power supply. Using an octal darlington driver, the circuit buffers and displays the state of the A5V (stdby), PS_ON, and VS_ON signals on LEDs. The PS_ON and VS_ON circuits include an R-C circuit to stretch out brief dropouts to aid in detection. The circuit has shown me that when the screen blanks, both the PS_ON and VS_ON go to their off states (3.3V and 0V, respectively) for the duration of the outage and seem to come back up with about the same relative timing as when powering up the set from scratch. The standby 5V remains steadily on. On occasions when the Samsung logo appears before recovering, the behavior is the same, just a little longer in duration.
This leads me to believe that the problem is in the main board. I am assuming it is supposed to hold PS_ON low when the set is on and also that VS_ON is slaved to PS_ON (either on the PS or logic boards, as it does not seem to connect to the main board). So my first question is: do you agree with my diagnosis that it's the main board?
Assuming the problem is on the main board, ideally, I'd repair the main board or have it repaired, but replacing is acceptable, too. I'm afraid that the intermittent nature of the problem will make it hard to pin down to a component. Are there any signals on the board I could similarly instrument to isolate further? I don't have a scope available, unfortunately, but can cobble together a circuit to monitor a relevant signal.
I see that the EEPROM is a common failure point in Samsung plasmas, but all the examples I've found in the forum fail hard immediately following power on, rather than being intermittent during steady viewing. Is the EEPROM actively accessed during steady-state operation or only at power-up and during state changes? If it is actively read or written in steady-state operation, I might attempt to replace it. I do have a brand new hot air soldering tool, the purchase of which I still need to justify. ;-)
Can anyone suggest other paths to pursue? I look forward to the community's suggestions.
Attached Files
Comment