HP 8569A Spectrum Analyzer: Any organ (ehh, CRT) donors out there

This 8569A came from the US, purchased by a local HAM operator, and in need of repair. Some switches don’t move nicely, so it seems liked a regular repair job of a 8569A.

First issue, 5 minutes after turn-on, where not the switches, but a blown mains capacitor (aging X2 grade capacitor). Well, this is easy to fix.

With the instrument powered on, it quickly became evident that the there is some distortion of the display, in particular, in the upper section of the CRT. This is not a common fault, and hard to explain other than by a broken deflection system of the CRT.

To be absolutely sure that no other assemblies are causing this defect, the X-Y deflection signals were coupled to a working 8569A, and indeed, no distortion visible.

The CRT display of a working 8569A – with the X-Y signals of routed from the unit that shows the distortions:

Sure, the display is not quite synced (also because of the extension leads with alligator clips). How to proceed? Well, this will need a 8569A CRT for repair, from a donor unit. Let’s hope, at least for the HAM friend that one will come around soon.

3 thoughts on “HP 8569A Spectrum Analyzer: Any organ (ehh, CRT) donors out there”

  1. Hello Simon,
    I dont believe that the distortion shown by the 8569A is caused by a faulty deflection unit, but instead by a sudden dip in the acceleration voltage of the crt.

    One reason I could think of might the improper grounding of the crt’s aquadag which serves as the filter capacitor for the high voltage.
    The reverse recovery current of the HV-rectifier would then give a short dip in the HV which leads to the increased deflection sensitivity.

    Regards
    Hans-Peter

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