Tek 576 noise and looping


peter bunge
 

The performance check/calibration that starts on page 5-4 was perfect up to step 16. Check Horizontal and Vertical Displayed Noise on page 5-15. The noise is twice what it should be for the horizontal and four times for the vertical. I 'scoped the power supplies and there is no ripple. Any suggestions?
I then switched to step 3. Locating Malfunctioning Circuits on page 4-5. Step D revealed that the rectified sine wave is flattened at the top and distorted on the right. This may be a cause of looping but not the noise problem. Any suggestions?
I have a parts unit that I decided to repair so I could compare signals. I had to remove the Collector switch box to repair shaft couplings so got to find out where the collector bridge rectifiers are and how to set up the shafts of the switches. I was surprised to find that the floating 50 volt supply is only 5 volts checked on both units with a 'scope and DVM. There is no ripple. It is plainly marked 50 volts in several places. Any comments?
I am going through the calibration on the second 576 but it is not looking good either.
Too bad I cannot show the photos here but if anyone wants my notes to get involved please ask off line.
PeterB

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