Quote:
Originally Posted by apple2dude
There are two 2.7 ohm voltage dropping resistors in the power supply. Bypassing one of them increases the overscan, so logically adding another would decrease it.
I don't have any of usable value or wattage at the moment, but in looking for one, is it a huge problem if the line voltage drops below a certain point?
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You need to verify the B+ is both on target *and* regulating with brightness. I'm assuming your regulator is OK because you never mentioned the overscan changing between light and dark scenes.
Adding or subtracting high wattage resistors is not the way to adjust B+. If you can post the power supply we can tell you how to lower B+ if you want to try it that way. If you fudge the pass resistors, you risk the B+ dropping under high demand scenes and the regulator running hotter.
Some of these use a self contained series/pass regulator IC like an STR30135 (guess). The way to lower this is to replace that regulator with an STR30130 which will lower you B+ from 135 to 130V.
If it uses all discrete components instead of the IC regulator, changing values of resistors and zeners in the regulator drive circuit will lower the B+ and still allow it to regulate tightly.
Regarding the sweep, there is a 330pf cap right on the collector of the horiz out to ground. You can remove that and see if your sweep is where you want it and your HV stays within the design specification.
Lowering B+ will reduce scan and lower HV
Reducing the value of the retrace capacitor will reduce the scan and raise the HV, so there is a choice to make.
John