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Fool for the 8656A Sig Gen

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Greetings EEVBlog forum - A newbie here, hope everyone is well and gettin' their nerd on. I'm a hobbyist focused on vintage audio and test equipment. Professional background is Architecture, but I've obtained a six year degree from UYT. (Thanks Dave, Paul, Tony, Clive, et al!).

I recently acquired an HP 8656A Signal Generator. Couldn't resist it for the price. Sold as a parts unit, but in pretty good shape overall. Serial number : 2146A02249, which I believe is a later model. Despite it's reputation, I'm going to give the thing a go. All 4 power rails appear to be good to go and the display lights up with basically nonsense. No response from any key. I went straight to the attenuator assembly for a quick look and the fault became obvious. The unit is missing two actuator rods and the actuator cover. The gold contacts for the actuator however, were bagged and stored in the unit. Since these parts are no longer made, my only options are 3D printing or getting lucky with an identical trashed unit that I could pull from. The thing that complicates the latter approach is that this attenuator assembly appears different than others I have seen, which have ball bearings on the forked actuator rods. Not so in my version. The ball bearings have been eliminated from the design.

So, finally getting to my question - Does anyone have a reliable source that could take a couple of the parts I have intact on other sections of the attenuator, scan them and 3D print me some duplicates? I've browsed around and it looks like the capability is out there. Tolerances and material selection are more detailed topics for discussion, but I need to start somewhere. Any suggestions?

Thanks in advance for any help! - JRH

Mechanical failure of the attenuator shouldn't cause anything other than incorrect/missing output levels.  You might want to sort all of the other problems out first before you go after that attenuator.  As far as the attenuator parts, I'm only familiar with the grommet/ball-bearing design, could you post good photos of what you have?  Is there a revision shown in a manual anywhere? 

Stray Electron:
   Where are you located?  I think there is (was?) the same unit in a surplus place about 60 miles from me.

   FWIW I hope that you got it CHEAP!  I hate buying TE that other people have been into. There is almost always parts missing or or it's damaged beyond repair.  When it comes to Ebay or when buying in person, I always check to see if the warranty seals are unbroken on the covers. If they're broken then the value of the items goes WAY down unless they're giving me a guarantee that the TE is working.

Thanks for weighing in Stray!

Yeah, I hear you. I did get it cheap, and wasn't expecting a working unit. My enjoyment comes from getting these boat anchors up and running again.
Appreciate the feedback. - JRH

A very good point bd, and food for thought moving forward. I had assumed that since the missing parts left an open circuit in an essential part of the unit, that I ought to start there, but your comment makes a lot of sense. I still have a lot of studying of the intimidating schematic to do, as well as researching revisions ahead of me. I've attached a photo of the plundered attenuator cavity.

Thanks so much for weighing in. -JRH


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