Z3801A help!

[5065AGuru]

I have a Z3801A GPSDO that has been running fine for well over 10 years. It recently lost the lock indication and I can't get it back! I did look at the work around to fix the problem with the outer oven controller getting confused and it did not fix my problem. However it did show that the outer oven was not powering on, even if I supplied the workaround pull up described. With 0v supplied the oven is supposed to be off and with +5V supplied the oven should be on. With the 5V applies the oven voltage is zero. I did notice that the resistors R112 and R113 near P2 on the top board seem odd. R112 looks to be soldered very poorly and R113 is missing completely! Does anyone have an opened up unit or the top board loose so they can let me know what R112 and R113 are supposed to look like? The schematic I have does not show R113. Appreciate it and any advice. When the unit failed it did seem as it was still in lock and on frequency but with no lock indicator.

Cheers,

Corby

[dietert1]

In order to get the lock indicator the oven needs to run. I would try and repeat the procedure with disconnecting the control signal, installing the pullup and waiting for some time, whether the control signal comes on. Using that procedure the oven should turn on.

I would test the GPS receiver first, looking at it's monitoring output. It needs to receive and track some satellites. Everything depends on a GPS lock.

One could also check the frequency of the OCXO. The OCXO might require adjustment to bring its tuning range back to 10 MHz +/- some margin required for lock. Aging also affects electrolytic caps, especially those near hot ovens, resistors or semiconductors. This kind of maintainance is justified after 10 years. The unit will be much easier to fix than a rubidium standard.

Regards, Dieter

[5065AGuru]

Well I got it running!

After a friend looked at his unit to determine the value of a resistor that was missing (I could tell someone had been working on the unit once I pulled the board!)  and does not show in the schematic, replacing the smaller 5V Dc-DC convertor, and doing the pullup trick it's working fine now.
The convertor I used was a 1.8Amp versus the 4.0Amp original but it runs just warm after a day of operation.

HOORAY!

Corby