Re: FG 502 Adjustment and Possible New Issue

Roger Evans

According to the manual R170 compensates for small offsets in the op-amps that control the positive and negative constant current sources that control the timing. The offsets are most noticeable for small voltages into the op-amps (ie the 0.1 end of the frequency dial. So R170 should compensate for item 4. in your list but have very little effect when the frequency dial is set to the upper half of its range.

My FG502 also has a small DC offset when the offset control is switched out, looks like R250 should adjust that, I will try it later on.

C287 (0.25 - 1.5pF) is only going to affect the very highest frequency components, ie the shape of the tip of the triangle at the switching point. Make sure the cable to the scope is terminated in 50ohm for best high frequency response.


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