Electronics > Repair

HP 3312A Frequency Drifting Downward

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Sipolandis:
I acquired an HP 3312A Function Generator that works in all regards, except that the output frequency drifts downward about 100 Hz/second. Any pointers to the likely culprit?

Swake:
As always start with checking out the power supplies thoroughly.
You could also post the schematic to make it little easier helping you.

Wallace Gasiewicz:
The 3312 frequency is determined by Resistance Capacitance circuits. There is no crystal reference.   
Any of the controls including the front panel potentiometers are suspect.  DIRT can cause this, so cleaning is a good first step.     
If you can leave it powered up for several hours safely, that may help also.       
Search for HP 3312 in the entire forum, there are numerous posts.   
Artek has good manuals for this unit, search for 3312           

http://artekmanuals.com/manuals/hp-manuals/

Manolo Mos:
I have this HP too. This defect is normal, is due to a mediocre design. The exact place of the component that provokes this drift in the small printed circuit, below, it was a metalic 8 pin circuit integrated. I don't remember which was. I'd don't use these instrument for frecuency precision works, it's clear it is don't made for this. Mine is keeped in a shelf, maybe someday goes to the electronic waste facility dump.

Sipolandis:
It's curious that this would be standard behavior for any HP gear. I have a couple of old vacuum tube signal generators that are rock solid. My best guesses are a capacitor that is drifting, or a thermally unstable transistor or IC.  I can leave it on for several hours and it keeps drifting downward.

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