Hi , I think the Regulator Board should still be questioned. To calibrate the +20 V,it is necessary to use an Extender Board because the calibration trimmer is not accessible with the card fitted normally. I have used the extender HP built for service model 5060-0049. After alignment I could see that the +20 Volt measured between the card A9 and A14(or other positions) have a variation of +50mV removing the extender. I repeated the test several times with the same result. The solution is to adjust the voltage with the extender to 19.95 volts and then remove the extender but a better solution will be to have a muti-turn trimmer accessible without removing the board.
Luciano On Thu 20/08/15 10:55 , "Poul-Henning Kamp" <p...@phk.freebsd.dk> wrote: > -------- > In message , > Bill Byrom writes: > > >I don't have an HP5065A and can only see the portion of the schematic > >you copied. > > The manual is on K04BB if you want the full monty. > > >Here is > >what I can surmise from your measurements (assuming you don't have > >any ground loops or measuring instrument or test lead thermoelectric > issues): > > The measurement setup isn't optimal, I can only do one measurement > every five seconds on each point and the HP34972A is only a 6½ digit > instrument, but otherwise the setup is solid. > > >The change of the 20 V power supply when you lock is roughly 400 > >uV (20 ppm). > > > >The change of the C-coil current isn't really repeatable. I see a big > >500 nA (111 ppm) drop at 1,000 seconds, but no such clear change earlier > >in the test. > > It didn't actually lock until 1000 seconds, so one difference is that > the logic "continous operation" logic didn't reach final state and > its lamp didn't turn on in the previous attempts. > > >But the actual voltage changes you are measuring seem to be > >roughly correlated between the 20 V power supply and C-coil current > >sense resistor changes. > > As they should be, because both are derived from the same A15CR5 zener. > > >I'm guessing about these values, based on converting your current > >numbers into voltage based on a perfect R10 || R11 parallel combination > >of 691.6 ohms. I see that R10 has an * asterisk, and I wonder what is > >shown for that note. R10 might be a selected value at manufacturer, or > >it might have a specific temperature coefficient. > > The asterix means "selected". I have not been able to figure out > what criteria it is selected for. > > >The temperature coefficient of the resistors may be much more important > >than anything else, especially for an old product. > > All the important ones are wire-wound, probably for exactly that reason. > > >those old electrolytic capacitors (C4, C6, and C7 for example) are still > >OK, or whether they are showing any changing leakage currents. You might > >want to change them with new capacitors just in case. > > Good point. > > >So I'm not convinced that the time curve is showing a correlation based > >on the 20 V power supply affecting the C-coil current. > > No, the main correlation is via the common zener, but the step at 1000s > is *not* present in the zener voltage, which means that the current > generator has really bad supply sensitivity. > > >It's possible that measuring system errors (such as where you connected > the > >measurement system ground) might cause some of these changes. So you > >might want to check your setup and the instrument and test lead > >computed accuracy. > > I think the way I've done it is OK. The 34972A has floating inputs > and I measure from a local GND for all six points. I'm not seing > any noise-artifacts. > > >I also disagree with your estimate of the CR5 zener current. [...] > >[...] > >the CR5 diode current must be (12.2195 - 4.2456 mA) = 7.9739 mA. > > Good point. > > >That's > >pretty close to the zero temperature coefficient current for the 1N938 > >you describe. So I do not recommend changing the diode current. > > The 7.5 mA optimum is from a much later data-sheet, and may be for > a particular "high performance" variant of the 1N938, so there is > no guarantee that there even is a zero-tempco current for the one > in my HP5065. > > Either way, fixing the zeners tempco is only half of the solution, > it looks to me like the "real" solution involves an entirely new > C-field current driver. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by > incompetence. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts [1] > and follow the instructions there. > > > > Links: > ------ > [1] > http://webmail.timeok.it/parse.php?redirect=https://www.febo.com/cgi-bin/ma > ilman/listinfo/time-nuts > Message sent via Atmail Open - http://atmail.org/ _______________________________________________ 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.