Hello, I posted this on the HP-Agilent group
https://groups.io/g/HP-Agilent-Keysight-equipment/topic/10811_serial_prefix_2023/84530740?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,0,0,84530740 but was redirected here. I'm debugging a faulty HP 8663A and am currently investigating the 10811A reference oscillator (the 8663A auxiliary fuse is blowing among other problems, so the oven could be at fault). There's a good manual for this online. However, both ko4bb and keysight have the same 2028+ manual. My version has prefix 2023. Additionally, I wasn't able to find much information on how the 60120 differs from other versions. It would great to get some advice on the symptoms I'm seeing. And, if anyone has a manual pertaining to this iteration of the oscillator, that would be incredible. There appear to be a number of differences between the 10811A in my instrument and the one described in the manual. Several examples (I haven't done a thorough search; this is just what I've noticed and there is probably more): - Q6 does not appear to be present in the 2023. - No thermal fuse (F1) in the 2023. - U1 is powered directly from the oven supply (not a 10 V regulator; I haven't yet figured out what U2 does in the 2023). - U1 directly drives Q7, rather than through a series resistor. My 10811 is not obviously faulty. In fact, I believe it's probably ok. But, the oven supply current draw is a little high (during warm-up and after settling) in comparison to what's stated in the manual. And, before I write it off as definitely not the problem, I'd like to get some more informed opinions. I measured the current draw as a function of time with the oscillator starting at room temperature (it was left unpowered for a day prior to this). I supplied +20VDC to the oven. Here are the results: | time (min) | current (mA) | |------------+--------------| | 0 | 510.6 | | 1 | 510.6 | | 2 | 511.8 | | 3 | 512.4 | | 4 | 513.0 | | 5 | 513.5 | | 6 | 514.1 | | 7 | 514.7 | | 8 | 233.0 | | 9 | 199.8 | | 10 | 181.2 | | 11 | 171.9 | | 12 | 166.1 | | 13 | 162.0 | | 14 | 158.5 | | 15 | 157.3 | | 16 | 156.2 | | 17 | 155.0 | | 18 | 154.4 | | 19 | 153.3 | | 20 | 152.7 | | 21 | 152.1 | | 22 | 152.1 | | 23 | 152.1 | | 24 | 150.9 | | 25 | 150.9 | | 26 | 150.4 | The precision I've given from about 8 minutes on is a bit misleading. The actual value oscillated about +/- 1 mA (the values before this appeared very stable). The manual stated that the oven current should not oscillate, but given the small amplitude of oscillation I figure this isn't something to worry about. Also, I assume the transistor heaters will need to turn on and off to maintain the temperature setpoint. I would expect this to create some oscillation in the current. The manual says that the warm up current should be between 380 and 490 mA for 5 to 10 min, followed by a decline and with the oscillator settling to a current between 60 and 150 mA after an additional 10 to 15 min. So, the currents are a little high. But, given this appears to be a different design and I can't actually find anything functionally wrong with the oscillator (the 10 MHz signal also appears fine), it doesn't seem to me that this is actually a problem. I also checked voltages against those specified in the manual when the oscillator was at room temperature. I've provided the results in the table below (as I mentioned earlier, Q6 doesn't appear to be present in this oscillator, so I checked other parts of the circuit to would normally be shorted to these Q6 nodes). | voltage point | oven cold (measured) | oven cold (target) | conclusion | |---------------+-------------------------------------+--------------------+---------------------------| | Q6B | starts just above 2, drops steadily | 2 | ✓ | | Q6C | 11.5177 | 11.4 | ✓ | | Q6E | starts at 1.5, drops steadily | 1.3 | ✓ | | Q7B | 12.7 and dropping | 12.7 | ✓ | | Q7C | 19.76 | 20 | ✓ | | Q7E | 11.5293 | 11.4 | ✓ | | Q8B | same as Q6E | 1.3 | ✓ | | Q8C | same as Q6C | 11.4 | ✓ | | Q8E | 280 mV | 0.23 | slightly high (TBD) | | U1 pin 1 | 1.63, dropping | 1.8 | slightly low (TBD) | | U1 pin 2 | 0.368 | 0.23 | slightly high (TBD) | | U1 pin 3 | 0.368 | 0.23 | slightly high (TBD) | | U1 pin 5 | 4.1697 | 4.1 | ✓ | | U1 pin 6 | 4.1725 | 4.1 | ✓ | | U1 pin 7 | 12.7, dropping | 4.8 | This is way off. But, | | | | | I think it may be ok, | | | | | since it appears U1 p7 | | | | | is shorted to Q7B. That's | | | | | probably just a version | | | | | change. | | U2 pin 2 | couldn't find this | 10 | | | U3 pin 6 | 18.646 | 19 | ✓ | Nothing appears obviously wrong. I think it's also worth mentioning a few other things that surprised me. The oscillator is about 10 years older than the 8663A. The 8663A has a serial prefix of 3043, whereas the oscillator (as already mentioned) has a serial prefix of 2023. It surprised me somewhat that HP would use a 10 year old reference oscillator in new synthesizer. But, I don't have enough experience to know whether this is normal or not. Also, the oscillator is labelled as an Agilent part. Apparently, Agilent wasn't formed until 1999, so presumably Agilent took an old oscillator and rebranded it. Is that correct? In any event, it sounds to me like this isn't the oscillator that was originally shipped with this frequency synthesizer. Best Matt _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.