Ed,
I just recalled a weird intermittent failure involving the 85662A A3A4 and A3A8 brds. The sweep ramp goes to both brds. if I recall correctly. The A3A8 digitizes the sweep ramp and when it hits the proper value it creates an EOS ( End Of Sweep) signal that then goes to A3A4 and the 8568 A22 brd (8566 A16brd). If the EOS is sent early then the Sweep is too short. If the EOS is late or not sent then you only have one sweep and no reset of the sweep. I have replace many 1826-0448 DAC’s for low order bit failures, if I recall correctly the replacement DAC may be 1826-0698?
The DAC’s were id’d as MSB and LSB ramp, sweep, sweep time, and EOS ramp DAC’s.
Also the failure symptoms were similar for too short of a sweep on the 8566 and the 8568, but drastically different between the 8566 and 8566 for the too long of a sweep.
Best regards,
Don Bitters
