[time-nuts] 5065A Problem

[John Miles]

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: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]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: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] 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
>
>
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