If you look at the EHT supply, fig5.3/2, you will see the grid supply windings on T200 (h,i) are floating, and the bottom end is fed from the Blanking Amplifier. If that is solved, then the end of the sweep disappears. Taking Nigel Goodwin's point about actual method of brightening the tube, on high speed scopes like this, the brightup pulse has to be DC coupled in some way, as otherwise the sweep has almost finished before the coupling capacitor has charged up enough. You didn't say whether the brilliance is uncontrollable, or turned up very high both indicative of Blanking troubles. ![]() But you do really need another scope (almost any will do) to check that a bight up pulse comes into the Blanking Amp from the TimeBase (pin6 T/B Z) and that the Brilliance control also works. Usually one of the two high voltage transistors will have failed. Look at the CRT Blanking circuit (I am quoting references from issue 2, 1973):Z Amplifier, PCB5, circuit fig 5.5/2. Hold-off alters the time after the end of a trace before it can be re-triggered, and so usually you will get a slower retrace on the screen. If you get more of the shaddowy trace, then that suggests my guess is right. Confirm this by getting the same trace as your picture, and then alter the "hold-off" control. ![]() Looking at your picture, I suspect the retrace blanking is not working properly.
0 Comments
Leave a Reply. |