[time-nuts] HP Z3801a insights and progress.

paul swed paulswedb at gmail.com
Sat Dec 17 15:59:10 EST 2016

Making serious progress on the ole basket case Z3801a.
Somethings that may be helpful to others.
Its easy to completely remove the 48 volt power supply and use a normal
bench supply. Especially if you are not using the outer oven and have a bad
ocxo. So all below without the ocxo and a TBolt 10 MHz feeding the 3801 ref
Red +5 at 57 ma
Yellow + 15 at 27 ma
Blue -15 at 0 amps very small.
The purple is a control wire and the green is a temp sense from the outer
Seems not to matter on these two. Though I sense (Pun intended) green does
need to be set.

How does the system tell when the OCXO is warm. Since the OCXO gets 24
volts by a +/- 12 V the sense must go negative to at least -9V.
this then signals the oven is warm. The rest of the 3801 starts working.

I suspect this same require can be used for the outer oven. Its unclear its
needed though.

By using an external bench supply the board becomes easy to work on after
the 48 V converter is taken off. This is a great way to troubleshoot.

More to learn.

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