[time-nuts] Z3801A OCXO manual trimming

Bob kb8tq kb8tq at n1k.org
Sun Mar 4 15:05:07 EST 2018


> On Mar 4, 2018, at 1:13 PM, Joe Hobart <nova at npgcable.com> wrote:
> My Z3801A failed about a year ago (there was a warning the electronic frequency
> control was nearing a limit).
> Symptoms (most from GPS Control and Lady Heather:
>   Frequency about 1E-8 low
>   Time Invalid  (many hours off)
>   Date 6 months old
>   DAC 99.9969 percent
>   Life 72K Hours
> Lady Heather shows the following as OK:
>   ROM, RAM, OSC GPS, Power, EEPROM, Antenna, Discipline, 5 satellites
> GPS Con shows the following:
>   EFC: ERR
>   No time display
>   Outputs Invalid
> Only the front panel power light is lit.
> This suggests either the crystal has aged or the heater temperature has drifted
> slightly.  I hear/read that opening the oscillator is difficult.  Is there a
> usable adjustment?
> What have others done to restore operation?  Is it time to consider a different
> time & frequency standard?

With enough effort and enough time spent troubleshooting, you probably can 
fix the beast. You might have to swap out the OCXO, but that’s still just a repair
process. The bigger question is indeed how much work to put in. 

The basic approach is to fire up a counter and get into the EFC voltage line.
Swing it to both limits and see what the frequency does. That will give you 
an idea if it’s the OCXO or if it’s the DAC side of things. 

The 3801 was made for a while. Some are hitting 20 years old at this point. 
Mine seem to eat power supply components from time to time. One of these
days, whatever it is that pops the fuse will do more damage. 

Back when the 3801 hit the surplus market there really was not a whole lot
else to look at. These days, we’re hip deep in a whole range of units sourced
mostly from “China Electronic Salvage Inc”.  Who knows …. maybe one day
there will be another TimeNuts TBolt “sale”…..


> Thanks,
> Joe, W7LUX
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