[time-nuts] OXCO Issues -- Latest

[Bob Camp]

Hi

They had cans with holes in them for the adjust process. There is no practical way to do the adjustment ahead of time. They turn hunt the parts first. Then a temperature test is done and they are adjusted again. The test / adjust process continues until they meet spec. The turn hunt gets things close, the test / adjust takes care of the (non trivial) contribution of temperature gradients and oscillator / buffer TC.

Bob

On May 12, 2013, at 6:45 PM, Frederick Bray <fwbray at mminternet.com> wrote:

> Interestingly, there is a hole in the foam to adjust the pot.  There is no corresponding hole in the can, only one for the piston capacitor adjustment.   It appears that the pot is part of the oven control circuit.  Maybe Ovenaire had a test fixture to make the adjustment before putting everything in the can?
> 
> I am about to the point where I will probably just reassemble it and drill a hole for the pot.  (That won't be hard to do after looking at the distance between the two existing holes in the foam and figuring out where the hole in the can should go.)
> 
> I have looked at the board under a lighted magnifier and can't see any cold solder joints or similar flaws.  I suppose I could heat each one up with a soldering iron to make sure.  I have tested all the resistors while in circuit and all values read less than or equal to the marked values.  I realize that it is still possible that one has increased but that due to other circuit components the reading is still less than the value of the resistor.  Perhaps I should just shotgun the ones in the oven control portion of the circuit?  I have found no open diodes.  I also have turned the pot 1/2 turn in each direction and returned it to its original position in the hope that this will have cleaned it.
> 
> I will have to go back into the power supply anyway.  There are a couple of strange things, such as the previously mentioned fluctuations on the 12 volt line.  Then, there is the fact that the -7 volt supply is still a volt too low.  It came up after I replaced some electrolytic capacitors and some out of value resistors but there's still more to do.  This doesn't impact the OCXO as it only uses 12 volts.
> 
> Thanks again for all the suggestions.
> 
> Fred
> 
> 
> 
> 
> 
> On 5/12/2013 3:16 PM, Don Latham wrote:
>> If there's a pot set that's inside the case, indeed inside the "foam"
>> then there has to be a procedure for setting it before final assembly,
>> no?
>> can't believe an engineering setup that requires tiny tweaks with
>> assembly and disassembly. . .
>> Don
>> 
>> 
> 
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