Bert asked me to send an update on the FE-5680 tempco mod progress.
It appears that the FE-5680A temperature signal (or maybe it's really a current sense signal?) can be disabled by removing a single 10k 0805 surface mount resistor.
Using Elio Corbolante's terrific high-res scans, I've noted the resistor location: http://www.n5tnl.com/time/fe-5680a/lobotomy.png
Why would you want to disable temperature compensation? As we've seen, the unit's firmware will adjust the DDS frequency as the temperature signal changes. If you're using the '5680 inside a control loop, it's likely to conflict. By removing the resistor, that channel of the 12 bit ADC will be tied to ground through an existing 2.21k resistor. The unit will see a constant 0 counts from the ADC and assume it's really cold.
I modified one unit and monitored it for a few hours over a range of temps, running it nice and hot with no heatsink, then blasting it with a fan and placing it on an ice-cold heatsink. I observed no change in the DDS tuning words.
It's a really easy mod--remove four screws, set aside the insulator sheet, and apply your hot leucotome/soldering iron.
I've also found a simple mod to replace the temperature signal with the output of the unused trimpot. This allows you to simulate any temperature you want. If there's any interest, I'll set up a test and monitor the DDS tuning words as the unit's firmware tries to adjust to the fake temp signal.
-- newell N5TNL _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
