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8566B - notches in response

 

Hi Vladan. Well, I built up 4 damping networks and performed an alignment on the 3MHz crystal IF in my 8566B, with the result that the notch can not be adjusted out? of the 1kHz response. The board is in beautiful condition, and none of the trimmers are damaged.
?If only one damping network is used to damp the crystal associated with C6 then the notches and a lot of the assymetry disappear, so I`m picking there`s a component failure in the area of C6, but where to go from there. I guess I could check the dc conditions around the active devices...Adjustment of C7 [centre, or null adjustment] works as it should, and adjustment of C6 moves the notch on the upper skirt of the 1kHz Res BW response up and down the skirt.
Do you wish to suggest which component might be faulty? Cheers!......................Don C.

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It would be good to see pictures of the notches. However, even without seeing the pictures, I would say that this looks like a problem with the SYM adjustment on the 3 MHz filter board. If the problem appeared suddenly, it may be a failed adjustable capacitor. If it showed up slowly, the filter probably needs adjustment. You will need to build the 3 MHz crystal bypass networks in order troubleshoot and adjust.

Still, it would be good to post some pictures before you take my word for it.

Vladan
 

My 8566B continues to work well after more than 30 years. On the 300 Hz Res BW setting there is a 15 dB notch apparent at center frequency?+1.2KHz, while on the 1KHz Res BW setting there is a 15dB notch at CF+1.5 KHz.. I`m thinking that there is a problem in the crystal filters. Has anyone struck this problem before? TIA for your consideration

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