Question about Panasonic PT-51G44 51" Rear Projection Television
I don't know your model of set very well. I will comment in general. I am assuming your set is using three CRT's for its projection system.
This is normaly a voltage regulation fault. As the CRT's pulls more current, the HV is dropping. A lower anode voltage means lower cathold current. What this does is lower the mass of the electron beam that is hitting the front phosphor in the tubes. Because of the lower electron mass, the deflection yoke has an easier time to pull or deflect the beam for scanning. And, thus the picture appears to increase in size.
If you look at low cost CRT TV sets, it is very common that the raster changes size a little with contrast and brightness change. This is because they use less quality of HV regulation.
Check the main power supply to see if it is stable with wide variation of picture contrast. Also, if you have an HV probe, check to see if the HV at the anodes of the CRT's is stable with changes in the picture contrast and brightness.
If the main power supply is stable, and the anode voltages are changing, then I would try the HV multiplier and flyback assembly.
This can also get a little complicated to troubleshoot. There is some regulation feedback reference from the HV drive that goes back to the HV generator circuit. There may be a fault in this area as well. Where this gets interesting to troubleshoot is where the horizontal scan drive is also the HV drive, as like most common CRT sets.
Some sets use scan compensation to also help for stability. They will control the gain of the scan amplifiers to help stabilize the scanning to make up the error difference in the HV regulation.
Posted on Apr 12, 2008
I would check the jungle ic.
Posted on Jan 30, 2008
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