Problem with my hp333 distortion analyser.

I used to service this line of analysers, but this was more than 15 years ago. I no longer have any documentation or notes. I do sort of remember that some of the caps in that unit would go shorted at times. Check for both high ESR caps, and shorted caps. Unfortunately you will have to remove the caps to test for shorted ones. The ESR meter will measure a cap that is resistive, as if it was good. Shorted or resistive caps are usually rare, but the types of caps used in this era of meter can do this. Start with the caps in the circuits associated to the auto reading first.

In some models of these meters, there is an optical block that uses a number of lamps and photo sensors. they are using optical coupling for auto biasing some circuits to achieve isolated DC balance. I have had some of these lamps and photo detectors go bad. HP no longer will supply parts or support for this meter, so whatever goes bad, you will have to substitute parts if possible. Atleast most of the components in this era of instrument are mainly generic, and can be purchased at most any electronics parts supplier. There are however some very critical germanium devices used in this meter. These will be very difficult to sub, even though they used to be very much available.