David McGaw wrote: > The 10811 is the newer SC cut crystal oscillator. The 10544 would be > the older AT cut oscillator. > > At 09:43 PM 10/14/2006, you wrote: > >> I got an HP 5370A from eBay which did not work at power up (display was >> messed up). After resetting all the ROMs and the CPU in their sockets, >> the instrument came to life and now powers up without error message. It >> has serial number 2128A01306. >> >> However, it seems that the reference oscillator output is severely >> distorted (when I look at it with the scope), it looks more like 900mV >> p-p of 30 MHz than 10 MHz, even though the instrument does not complain. >> The output looks the same if I drive the external reference or use the >> internal reference. When I measure the reference output with the 5370 >> itself, I can make it display 10 MHz, 20 MHz or 30 MHz just by adjusting >> the threshold pot. >> >> I have posted a picture at http://www.ko4bb.com/Test_Equipment/HP >> 5370A_ref_output.jpg >> >> Also, I went through the instrument check out, and the first step, page >> 3.4, shows how to read the period of the reference oscillator, and the >> instrument displays 0.00 instead of 100.00. It obviously does not like >> the reference output signal. >> >> The time base is an 10811-60111, I believe this is the "standard" time >> base, as the manual lists the "high Stability" time base as a >> 10544-60011. The 10811 is a pretty nice "standard" time base :-) >> >> Otherwise, the time base seems very close, my reference oscillator (a >> 3586 synchronized to WWV until my GPS clock is finished) displays 10.000 >> 000 100 on the 5370. >> >> So it seems some of it is working, but the reference oscillator output >> bothers me, and so does the impossibility to run the check out.. >> >> Any help in figuring out if this is normal would be appreciated. >> >> >> Thanks in advance. >> >> Didier KO4BB >> >> >> _______________________________________________ >> time-nuts mailing list >> time-nuts@febo.com >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> > > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > Didier
The path from the external frequency input to the external 10MHz input is 1) single transistor buffer/multiplier with collector tank tuned to 10MHz 2) Single transistor amplifier/multiplier with collector tank tuned to 10MHz 3) ECL gate chain 4) longtailed npn transistor pair which has a capacitively tapped LC tank circuit tuned to 10MHz. The path from the internal crystal is via a set of ECL gates The internal or external source is selected both by a set of ECL gates and by a slide switch to minimise feedthrough. Since the only common circuit other than a few ECL gates is the longtailed pair with a tuned collector tank, it is possible that the collector tank components are tuned to 30MHz and not 10MHz. One of the tank components may have failed or there may be a dry joint or equivalent in the tank circuit. The collector tank is excited with a squarewave current source which has 3rd, 5th, 7th harmonic components as well as the fundamental. You should check the signal path through the A8 reference frequency buffer assembly board. There may also be other problems but you need to isolate and fix them one at a time. Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
