My HP8563E (3305A00721) has had a YTO replacement. Now it is error free upon start-up and seems to work fine. However, if I look at the cal signal at 300 MHz and reduce Span from about 13.5 MHz to 6.8 MHz by rotating the knob, the signal disappears from the screen. Outside this range all is fine. So I guess the YTO is fine. I suspect the FM coil driver. The Service Guide I have (08563-90214, March 2001) has a test procedure at page 570, I followed. Check no 3 is ok. Check 4 also ok but with a glitch in the middle of the horizontal part of the scope image. There is no picture of what the scope is supposed to show. Then I checked table 10-15 on the next page. This contains an error as U318 does not exist. I suppose I need to check U317 that exists and is a switch device. I have the CLIP. However I can not reproduce the table: I see H (pin 1), H(8), L(9), H(16), in stead of HLLH as given in said table. As there is no description of how this circuit (the Span Attenuator) works it gets a bit misty here.
Any help in solving this problem is greatly appreciated.