Re: FG 502 Adjustment and Possible New Issue


Stephen
 

On Tue, Aug 4, 2020 at 10:14 PM, Roger Evans wrote:


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.

Roger

I actually figured out (I think) what R170 was doing. It adjustS the horizontal symmetry of a square wave signal. You adjust for the same length (pos and neg sides). And that also affects the triangle shapes as well... Hence my weird looking triangles when I messed with it.

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