[time-nuts] Fixed my 1804M

[Paul Flinders]

On 25/07/12 22:18, Chuck Forsberg WA7KGX N2469R wrote:
> How about a 10 MHz OCXO and a divide by two chip?   Maybe an op-amp to 
> change and/or invert
> the control voltage?
In the end that's exactly what I did.

Details on eevblog - 
http://www.eevblog.com/forum/projects-designs-and-technical-stuff/rapco-1804m-repair-10mhz-conversionbodge-(-teardown)/

Found a 10MHz ocxo which seems to have very similar specs to the 10Mhz 
1804Ms running without GPS and dropped that in.

There's a handy 22ohm damping resistor in the track which takes the 5MHz 
round to the logic so lifting that allows one to insert a divide by two 
bodge, leaving 10MHz at the rear BNC. Didn't have too many problems 
achieving "fine" control for the oscillator - took about 24 hours, 
although I did tweak the DAC output manually to be in the right ball 
park - it needed quite a large shift & I wasn't sure whether the 
firmware would make such a large correction, or take a very long time to 
do it.