[time-nuts] 5065A Problem

J. L. Trantham jltran at att.net
Wed Feb 10 14:10:26 UTC 2010


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




More information about the time-nuts mailing list