[time-nuts] HP Z3805A GPSDO Oven Heater Voltages

Henry Hallam henry at pericynthion.org
Thu Apr 24 18:31:32 EDT 2014


John,

I have a similar unit (probably from the same seller), advertised as
an Z3805A upgraded to the features of 58503A, whatever that is
supposed to mean.

Mine also does not get warm on top, though it appears to be providing
a decent 10 MHz output and indicates GPS lock.  This is the best
reference in the lab at the moment so I can't truly speak to the
stability of the output.

Thanks for the heads-up that the outer oven is not being turned on by
the CPU.  I haven't opened up the case yet but will do so as soon as
my order of round tuits arrives :)

Henry

On Thu, Apr 24, 2014 at 10:15 AM, John Stuart <j.w.stuart at comcast.net> wrote:
> Jarl,
> Thank you for your help on this.  It appears that either; the CPU has a bad
> output pin, some unknown command has turned the heater off, or the firmware
> is programmed that way.  The 10 MHz frequency had always been very 'stable',
> and I didn't know there was a problem until I bought a 2nd HP Z3805A and
> felt how warm the (50C) insulated double oven should feel.
>
> I am trying to communicate with the seller in Hong Kong.  So far he hasn't
> acknowledged that the CPU output pin can turn-off the heater.
>
> By the way, your projects on    <http://risums.net/hjem/oz9mo/index.html>
> http://risums.net/hjem/oz9mo/index.html  are very interesting and described
> very clearly.  Nice work!
>
> John, KM6QX
>
>
>   _____
>
> From: Jarl Risum [mailto:jarl.risum at gmail.com]
> Sent: Thursday, April 24, 2014 5:23 AM
> To: John Stuart
> Subject: Re: HP Z3805A GPSDO Oven Heater Voltages
>
>
> John,
>
>
> Thanks for the feedback and congratulations with your result so far.
>
> Unfortunately I have no further information regarding the function of the
> outer oven control signal from the processor board. You are probably right
> in assuming that the signal might be used to prevent the outer oven from
> overheating in case the thermistor went open, since the processor on the
> main board do monitor the outer oven heater voltage through P2/9.
> Speculating further: It might also be used by manufacturers to switch off
> the outer oven heater circuit permanently in HP Z3805's using the 5 MHz MTI
> OCXO if a suitable RS-232 command exist for this purpose.
>
>
> Cheers from OZ9MO / Jarl
>
> in Denmark
>
> Some of my Time-Nuttery:  http://risums.net/hjem/oz9mo/index.html
>
>
>
>
>
> 2014-04-24 3:13 GMT+02:00 John Stuart <j.w.stuart at comcast.net>:
>
>
>
> Jarl, OZ9MO
> Thank you for those two links!  They have the information I needed, and are
> very well 'hidden' on the internet.
>
> I have had partial success.  Per the work-around on www.realhamradio.com, I
> pulled P2-8 on the power board up to +5V, and the outer heater came on and
> is now being controlled by temperature controller on the power board; TP104
> is modulating around 15.75 V.
>
> However the heater on/off control signal from the main circuit board
> (normally connected to P2-8) is still OFF at 0.0 V.  For some reason (maybe
> firmware) the units CPU is not turning on this signal.  I am thinking about
> permanently wiring +5V to P2-8 to keep the heater enabled.
>
> Why would the outer oven ever be turned OFF ??  Maybe to prevent
> over-temperature damage if the NTC sensor fails?
>
> When I bought this "HP Z3805A" from the Hong Kong seller a couple of years
> ago, it was advertised as having been upgraded to the features (firmware?)
> of the HP(Symmetricam) 58503A.  Does anyone else have this 'model' and does
> the Double Oven XO keep the unit's top very warm, like it should?
>
> John Stuart, KM6QX
> Lafayette, CA
>
>
>
>   _____
>
> From: Jarl Risum [mailto:jarl.risum at gmail.com]
> Sent: Wednesday, April 23, 2014 2:22 AM
> To: j.w.stuart at comcast.net
> Subject: HP Z3805A GPSDO Oven Heater Voltages
>
>
> Hi John
>
>
> You will find a comprehensive description of the outer oven heater circuit
> here:
>
> http://www.ko4bb.com/Manuals/05%29_GPS_Timing/Z3801/Z3801A_Outer_Oven/Web_Pa
> ge/Z3801A%20Outer%20Oven%20Controller.htm
>
>
> In my HP Z3805A the outer oven circuit is identical to the circuit in HP
> Z3801.
>
>
> A description of a Z3801A outer oven fault similar to the one you have can
> be found here:
>
> http://www.realhamradio.com/oven-confusion.htm
>
>
> You will also find a suggestion for a simple remedy.
>
>
> Good luck.
>
>
> Cheers from OZ9MO / Jarl
>
> in Denmark
>
>
>
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