I have a hp z3801 that is spare parts it never worked correctly. Did some digging and at least one major issue is the actually HP 10811 is 38 Hz low. It needs to be within a Hz. Checked everything feeding voltage and such and they are solid at 5.7V from the regulator. The varicap works as expected. Signal levels out are clean and correct. Temp is about 82C also inline. The oscillator is actually fairly simple. Do xtals just fail after many years? May see if I can map a Piezo oven oscillator into the z3801 just to see what if anything happens. Now that I know the warm oven signal drops fromm 22V to 3.8V when hot. Fake it out. Not sure the outer oven actually matters on the z3801. But even that can actually be hooked up to make any circuit that might want to know thats it hot happy. Regards Paul WB8TSL

Hi Crystals do indeed fail. In the case of 40 Hz low, I’d look for a shorted cap in series with the crystal. Bob > On Dec 14, 2016, at 5:23 PM, paul swed <paulswedb@gmail.com> wrote: > > I have a hp z3801 that is spare parts it never worked correctly. Did some > digging and at least one major issue is the actually HP 10811 is 38 Hz low. > It needs to be within a Hz. Checked everything feeding voltage and such and > they are solid at 5.7V from the regulator. The varicap works as expected. > Signal levels out are clean and correct. Temp is about 82C also inline. > The oscillator is actually fairly simple. Do xtals just fail after many > years? > May see if I can map a Piezo oven oscillator into the z3801 just to see > what if anything happens. Now that I know the warm oven signal drops fromm > 22V to 3.8V when hot. Fake it out. > Not sure the outer oven actually matters on the z3801. But even that can > actually be hooked up to make any circuit that might want to know thats it > hot happy. > Regards > Paul > WB8TSL > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

Bob Took your advise and did check all of the caps in teh oscillator along with resistors. All are as they should be. Though they do differ from the schematic I have for the HP 10811. But thats normal reality on HP stuff. So it is a sick 10811. So at this stage I have jacked a external 10 MHz reference into teh system to replace it and the rest of the Z3801 seems to be working. It needs more time but did acquire satellites. It hasn't locked yet and unsure it can with an external reference unless I use the TBOLT 10 MHz. Kind of liking that idea. Since the oscillator was bad and thats how I received it several years ago the DAC is at 99.99% full scale because it was 40 Hz low. Want to reset that to mid range. Also I speculate the actual gps receiver is down on sensitivity but I do have replacements. Regards Paul. On Wed, Dec 14, 2016 at 7:10 PM, Bob Camp <kb8tq@n1k.org> wrote: > Hi > > Crystals do indeed fail. In the case of 40 Hz low, I’d look for a shorted > cap in series with the crystal. > > Bob > > > On Dec 14, 2016, at 5:23 PM, paul swed <paulswedb@gmail.com> wrote: > > > > I have a hp z3801 that is spare parts it never worked correctly. Did some > > digging and at least one major issue is the actually HP 10811 is 38 Hz > low. > > It needs to be within a Hz. Checked everything feeding voltage and such > and > > they are solid at 5.7V from the regulator. The varicap works as expected. > > Signal levels out are clean and correct. Temp is about 82C also inline. > > The oscillator is actually fairly simple. Do xtals just fail after many > > years? > > May see if I can map a Piezo oven oscillator into the z3801 just to see > > what if anything happens. Now that I know the warm oven signal drops > fromm > > 22V to 3.8V when hot. Fake it out. > > Not sure the outer oven actually matters on the z3801. But even that can > > actually be hooked up to make any circuit that might want to know thats > it > > hot happy. > > Regards > > Paul > > WB8TSL > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >

Hi If it is a crystal, a broken seal on the can is a pretty good guess. Often this runs up the resistance as well. Bob > On Dec 15, 2016, at 8:57 PM, paul swed <paulswedb@gmail.com> wrote: > > Bob > Took your advise and did check all of the caps in teh oscillator along with > resistors. All are as they should be. Though they do differ from the > schematic I have for the HP 10811. But thats normal reality on HP stuff. So > it is a sick 10811. > So at this stage I have jacked a external 10 MHz reference into teh system > to replace it and the rest of the Z3801 seems to be working. It needs more > time but did acquire satellites. It hasn't locked yet and unsure it can > with an external reference unless I use the TBOLT 10 MHz. Kind of liking > that idea. > Since the oscillator was bad and thats how I received it several years ago > the DAC is at 99.99% full scale because it was 40 Hz low. Want to reset > that to mid range. > Also I speculate the actual gps receiver is down on sensitivity but I do > have replacements. > Regards > Paul. > > On Wed, Dec 14, 2016 at 7:10 PM, Bob Camp <kb8tq@n1k.org> wrote: > >> Hi >> >> Crystals do indeed fail. In the case of 40 Hz low, I’d look for a shorted >> cap in series with the crystal. >> >> Bob >> >>> On Dec 14, 2016, at 5:23 PM, paul swed <paulswedb@gmail.com> wrote: >>> >>> I have a hp z3801 that is spare parts it never worked correctly. Did some >>> digging and at least one major issue is the actually HP 10811 is 38 Hz >> low. >>> It needs to be within a Hz. Checked everything feeding voltage and such >> and >>> they are solid at 5.7V from the regulator. The varicap works as expected. >>> Signal levels out are clean and correct. Temp is about 82C also inline. >>> The oscillator is actually fairly simple. Do xtals just fail after many >>> years? >>> May see if I can map a Piezo oven oscillator into the z3801 just to see >>> what if anything happens. Now that I know the warm oven signal drops >> fromm >>> 22V to 3.8V when hot. Fake it out. >>> Not sure the outer oven actually matters on the z3801. But even that can >>> actually be hooked up to make any circuit that might want to know thats >> it >>> hot happy. >>> Regards >>> Paul >>> WB8TSL >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

I had a reference problem on my Z3801A years ago, and ultimately found that the opamp that controls the 10811 oven temperature was bad. I think it turned out there was a bad batch of certain date codes. Replacing the IC with an equivalent type fixed it right up, with no other changes or adjustments. Also note that the the ovens are sequenced to avoid drawing too much power from cold-start. As I recall, the inner one has to get up near operating temperature to get things running ASAP, then its status signal enables the outer oven driver (a switched-mode converter on the Z3801A power supply board) to start - it takes longer to stabilize. I think the inner oven should take maybe 20-30 minutes tops, to reach the spec range, and the outer one gradually catches up over maybe an hour or two. The crystal is very sensitive to temperature until it gets to turnover, so the frequency can seem way out of whack compared to its normal operating point. The oven temperature doesn't have to be very far off to cause this, so a failure in the inner oven control that throws it out of range could cause problems. Ed

Hi The “outer oven” on the Z3801 10811’s is simply a warmup heater to improve performance when the unit starts at -40C. When operated as designed, it is effectively “gone” in normal operation. The 10811’s normal oven circuit (“inner oven”) on the modified 10811 is still what does all of the stabilization of the crystal. The temperature stability of the Z3801 version is not significantly different than the standard 10811 when measured over a normal ambient range. Since our basements are rarely at -40C there is not a lot of value to the "outer oven" in the standard configuration. A proper outer oven / inner oven combination would be designed and configured very differently than what you see in the Z3801. The “boost heater” approach does show up in other gear, very little of it is in TimeNuts stuff. Why do it this way? The 10811 as built simply did not have enough power to warm up properly from -40. At the time, there was some thought that GPSDO’s would be deployed in un-heated enclosures (that never happened). To get the unit working, a number of “quick and dirty” hacks were employed to hook the existing OCXO into the Z3801 design. They were of a “fast time to market” nature rather than “figure it out and do it right”. Bob > On Dec 16, 2016, at 12:44 PM, ed breya <eb@telight.com> wrote: > > I had a reference problem on my Z3801A years ago, and ultimately found that the opamp that controls the 10811 oven temperature was bad. I think it turned out there was a bad batch of certain date codes. Replacing the IC with an equivalent type fixed it right up, with no other changes or adjustments. > > Also note that the the ovens are sequenced to avoid drawing too much power from cold-start. As I recall, the inner one has to get up near operating temperature to get things running ASAP, then its status signal enables the outer oven driver (a switched-mode converter on the Z3801A power supply board) to start - it takes longer to stabilize. I think the inner oven should take maybe 20-30 minutes tops, to reach the spec range, and the outer one gradually catches up over maybe an hour or two. > > The crystal is very sensitive to temperature until it gets to turnover, so the frequency can seem way out of whack compared to its normal operating point. The oven temperature doesn't have to be very far off to cause this, so a failure in the inner oven control that throws it out of range could cause problems. > > Ed > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

Great comments. I can confirm the oven behaviors. The out is not needed. It is controlled from the micro and warms slowly at about 17 volts. Gets to 150 F after a solid hour as long as its insulated other wise it has a hard time keeping up with ambient air. The 10811 does heat quickly to the 85C. I have measured it and it is heating to 85. So unfortunately not my lucky day. Opamp would be a piece O-cake. So all that said time to move on. By injecting 10 MHz from a TBolt I hoped to get things running. Just to see. But I think I have a second issue. HP satstat and gps control report the OCXO warming up. Never gets to the hot point. Now the 108011 is out of circuit and per the 10811 manual I am supplying a 3.5V signal to the cpu. But it never changes state. The second issue was the bad 10811 has made the DAC goes to 100%. So far no luck in it changing. But of the ovens not warm I could see why the system would not adjust the EFC. I am hoping away from 100%. A system preset does tell the DAC to go to a mid range level but after some 10 or seconds it jumps back to max. I almost might believe I would need to do a fast dance. restart and very quickly tell it to write the data to eeprom. I am not that fast. Have been searching th net for clues about reseting teh dac. No luck. Regards Paul WB8TSL On Fri, Dec 16, 2016 at 3:02 PM, Bob Camp <kb8tq@n1k.org> wrote: > Hi > > The “outer oven” on the Z3801 10811’s is simply a warmup heater to improve > performance when the unit > starts at -40C. When operated as designed, it is effectively “gone” in > normal operation. The 10811’s normal > oven circuit (“inner oven”) on the modified 10811 is still what does all > of the stabilization of the crystal. The > temperature stability of the Z3801 version is not significantly different > than the standard 10811 when measured > over a normal ambient range. Since our basements are rarely at -40C there > is not a lot of value to the "outer > oven" in the standard configuration. A proper outer oven / inner oven > combination would be designed and > configured very differently than what you see in the Z3801. The “boost > heater” approach does show up in > other gear, very little of it is in TimeNuts stuff. > > Why do it this way? The 10811 as built simply did not have enough power to > warm up properly from -40. At > the time, there was some thought that GPSDO’s would be deployed in > un-heated enclosures (that never happened). > To get the unit working, a number of “quick and dirty” hacks were employed > to hook the existing OCXO into > the Z3801 design. They were of a “fast time to market” nature rather than > “figure it out and do it right”. > > Bob > > > > On Dec 16, 2016, at 12:44 PM, ed breya <eb@telight.com> wrote: > > > > I had a reference problem on my Z3801A years ago, and ultimately found > that the opamp that controls the 10811 oven temperature was bad. I think it > turned out there was a bad batch of certain date codes. Replacing the IC > with an equivalent type fixed it right up, with no other changes or > adjustments. > > > > Also note that the the ovens are sequenced to avoid drawing too much > power from cold-start. As I recall, the inner one has to get up near > operating temperature to get things running ASAP, then its status signal > enables the outer oven driver (a switched-mode converter on the Z3801A > power supply board) to start - it takes longer to stabilize. I think the > inner oven should take maybe 20-30 minutes tops, to reach the spec range, > and the outer one gradually catches up over maybe an hour or two. > > > > The crystal is very sensitive to temperature until it gets to turnover, > so the frequency can seem way out of whack compared to its normal operating > point. The oven temperature doesn't have to be very far off to cause this, > so a failure in the inner oven control that throws it out of range could > cause problems. > > > > Ed > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >