AbhishekGhosh
New Member
- Joined
- Dec 21, 2023
- Messages
- 4
I have many Samsung SyncMaster 753s Monitors. But in most of them, I guess the focus has become thermal sensitive. The focus drifts over time. The focus does not remain constant over hours of usage. (This is not the case with later model models of Syncmaster, for example, 793s, which I also own).
The focus drifts. After drifting, it can be brought back to crisp focus using the flyback controls. But as the set warms up even more, it goes out of focus again, and again, you can adjust the flyback to get a crisp picture (but then again, when you switch the monitor off and use it again, say the next day, the set is out of focus, and you need to reach that point (say 4 hours or 5 hours) to get to that crisp focus adjustment which you did when the set was hot and ran for 4 hours.). Also, suppose the set gets out of focus (very slightly) after about 1-1.5 hours of use; switching the monitor off and giving it some rest for about 10-15 mins brings it back to the crisp focus.
The geometry/raster does not change. Also, running the monitor with the back cover off slows down the focus drift to a great extent.
I see (in the manual) that the dynamic focus control circuit drives the focus from the flyback, and I suspect that with heat, it is this circuit that is causing a change in the focus voltage from the flyback to the CRT socket (That is my guess, but I might be wrong).
The Service manual troubleshooting section which talks about focus:
Which in turn talks about the Dynamic Focus Failure Troubleshooting section:
The circuit around Q551 is attached below:
The circuit around T502:
I have attached the Service Manual [Syncmaster_753s.pdf]
Did anyone face the same issue? How do you think I could fix this?
The focus drifts. After drifting, it can be brought back to crisp focus using the flyback controls. But as the set warms up even more, it goes out of focus again, and again, you can adjust the flyback to get a crisp picture (but then again, when you switch the monitor off and use it again, say the next day, the set is out of focus, and you need to reach that point (say 4 hours or 5 hours) to get to that crisp focus adjustment which you did when the set was hot and ran for 4 hours.). Also, suppose the set gets out of focus (very slightly) after about 1-1.5 hours of use; switching the monitor off and giving it some rest for about 10-15 mins brings it back to the crisp focus.
The geometry/raster does not change. Also, running the monitor with the back cover off slows down the focus drift to a great extent.
I see (in the manual) that the dynamic focus control circuit drives the focus from the flyback, and I suspect that with heat, it is this circuit that is causing a change in the focus voltage from the flyback to the CRT socket (That is my guess, but I might be wrong).
The Service manual troubleshooting section which talks about focus:
Which in turn talks about the Dynamic Focus Failure Troubleshooting section:
The circuit around Q551 is attached below:
The circuit around T502:
I have attached the Service Manual [Syncmaster_753s.pdf]
Did anyone face the same issue? How do you think I could fix this?