[time-nuts] 5065 photo/lamp problem

[Magnus Danielson]

Hi Corby,

On 2020-01-06 23:02, cdelect at juno.com wrote:
> Magnus,
>
> If you apply a +20V supply to the lamp connector you should see 125-150ma
> unlit and it drops  bit when it lights.
I see about 1,23 V over the 10 Ohm resistor, matching up with that current.
> Also measure from the lamp connector center pin to the outside conductor
> with an Ohmmeter.
>
> You should have around 3.33K. The 1.33K resistor (in series with a 2.0K)
> is a common problem. it can open up or rise in value.
>
> I usually replace this resistor in units I service even if it measures
> good.
>
> I use a 1.3K 2% MOX resistor.
>
> Also check the approx. 12 Ohm resistor on the standoffs to see if it
> opened up.

Both these resistors where good, but fractured. I already replaced the
10 Ohm resistor (put a pair of 22 Ohm resistors in parallel so they can
handle the power better) and is about to replace the 1.33k resistor.

Nothing else looked terrible bad and as far as I was able to
quick-measure the resistor did not seem broken, but I consider replacing
that regardless, but I will check it again.

>
> If  you pull the lamp assy. you can place a spec-A lead and see the RF.
> Should be approx 88Mhz. (not critical)

Before opening up the assembly I sniffed the J16 connector for something
in that neighborhood, but no.

I forgot to sniff again with the hood off. However, I let it sit there
for some time without any actual light from the lamp. I did see light
coming in from the side and thought that this was the lamp, but no.

> Once power is applied the lamp  should start (cold) within a minute or
> so, warm it starts fast.
>
> If you place a scope on A7 TP2 and with the lamp assy removed allow some
> florescent lighting to fall into the interior you should see a large 50
> or 60Hz signal from the light falling on the photocell.

I was considering doing exactly that, but I concluded that the lamp does
not lit so I thought I would want to start with that anyway.

Thank you for your input so far. It seems like I'm not completely off
the mark even if I have yet to find the real fault of that rubidium lamp.

I borrowed the A15 board over to the other broken 5065 in order to
support another measurement campaign, and while that second 5065 is
noisier that the 5065 that is operational (on its own) it was quieter
than the OSA 3210 and 5071A cesiums. The aim is to repair both 5065s
that is broken so I have three operational. Once they are all working, I
will do a trim campaign on them. I was amazed at how much noisier
(factor of 3-4 times) the older unit was compared to the newer.
Phase-noise of the synthesizers is not stellar by any means, my 3325B is
cleaner by far, and I only used a spectrum analyzer to compare them
while the TimePod was busy doing other things.

Right now the main goal is to get as much as possible online to see just
what set of devices is able to make the TimePod eat into the noise and
characterize the EFOS10... because it's a fun challenge and a chance to
characterize things. It is also good to have those curves as reference
as one measure things. Currently my best 5065A and a BVA is given a
shot, but since the BVAs was brought online the other day, it is clearly
drift-limited.

I have 5 large rubidiums, it would be nice to have them all operational
and see how they behave. Then I have cesiums to test... and OCXOs, and
GPSDOs... yes, lab-time is fun again.

Talking about GPSDOs, I have two home-brew GPSDOs that I've been firing
up, one is build by late Lars Wallenius, and another by AE6RV GFS-6A
GPSDO. The Trimble Thunderbolt seems happy right now, but my Trimble
NetRS is not seeing any satellites.

Cheers,
Magnus