True, photo current should still be present if you have cell flooding. Only the second harmonic would be affected by that. Amplitude should be stable immediately after power-up, so my guess is there's a supply regulation problem. Check the supply voltage to the OCXO, and if OK, check the output level at the oscillator itself?
-- john, KE5FX > -----Original Message----- > From: [email protected] [mailto:[email protected]]on > Behalf Of J. L. Trantham > Sent: Wednesday, February 10, 2010 6:10 AM > To: 'Discussion of precise time and frequency measurement' > Subject: Re: [time-nuts] 5065A Problem > > > John, > > Thanks for the reply. > > I don't know the history, just got it. When first plugged in, Photo I and > 2nd Harmonic go full scale then promptly come back to 0 (center). Supply > indicates normally, Lamp Oven, Cell Oven and Osc Oven all go full > scale and > stay. After about 20 to 30 minutes, they come back on scale and seem to > indicate normally as compared to what the manual says. 5 MHz indicates > normally though it takes a few minutes for it to 'warm up' to the proper > amplitude. 1 MHz and 100 kHz do not indicate when the Start switch is > cycled until after 30 or 40 minutes of warm up. Then they come on scale > normally. When hooked to a scope, at 50 ohms, their amplitude essentially > disappears. I suspect a problem there. Still visible at 1 Meg input > impedance. Control and Error stay at 0. So, I think all indications are > normal except Photo I and 2nd Harmonic. > > I read about the cell flooding issue and how to deal with it in the manual > but I was expecting Photo I to give an indication in the presence of cell > flooding. Should there be an indication on Photo I in the > presence of cell > flooding? If not, then clearly I need to go through the cell flooding > steps. > > J16 indicates about 19.987 VDC I did not measure the current at > J16. I'll > have to go back and do that. > > Joe > > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of John Miles > Sent: Tuesday, February 09, 2010 11:51 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] 5065A Problem > > > Suggestions: > > 1) Was it working before? If not you may need to follow the cell-flooding > correction procedure in the manual. Corby Dawson made an informative post > about that phenomenon a couple of years ago, if you can find it in the > archives. > > 2) If it was working but failed, check the +20V supply at J16 > first. If the > voltage at that jack is OK but no current is being drawn, the Colpitts > oscillator that drives the lamp has failed. Nothing else will work until > you open the RVFR and fix the oscillator -- which is possible but not much > fun. > > Suggest checking the ESR of all of the capacitors on the A11 oven > controller > before you put it back into service. When I got my 5065A I had > to replace a > resistor on the oscillator board that had physically cracked from > overheating. Both C23 and C24 on A11 were open; so were the same two 20 > uF/50V capacitors on the battery-charger board. > > I don't immediately see how that could have caused the oven controller to > run away, but it was pretty clear that it had happened at some > point. Either > way, if the lamp or cell oven current hasn't decreased within > 20-30 minutes > after turnon, you need to power it down and look for a controller problem. > > -- john, KE5FX > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
