HP 8640B sig gen 512...1024MHZ range not working

[PartialDischarge]

Have a 8640B in which the range 512..1024MHz is not connecting, output frequency stays the same as in range 256...512MHz.
Everything looks fine inside, before I read the service manuals is there anyone who has had this problem before?

[PartialDischarge]

Oh I know what happened, the metal strips in the rotary switches are falling down...

[factory]

Not had this problem, but neither of mine (8460A & 8460B) have the internal doubler option fitted, the control has labelling for the 512 to 1024MHz but requires an external doubler.

The switch contacts falling out is a very common problem with both the 8640 and SA plug-ins for the 180/181/182 series SA.

David

[PartialDischarge]

I disassembled everything and secured all contacts with UV glue, now works fine.
Everyone with this equipment should do this as preventive maintenance, it’s bound to happen sooner or later

[Zenith]

The other notorious problem with the HP8640A/B is the nylon gears, which crack with age and can't be easily fixed with glue. There are articles on moulding new ones and at one time someone sold brass replacements. The ones on my 8640A are cracked. I just take it very easy when I use it as I can't face up to replacing them.

The analogue scale on the 8640A is rather delicate and suffers from age as well. Fortunately I found a replacement for mine.

[PartialDischarge]

The other notorious problem with the HP8640A/B is the nylon gears, which crack with age and can't be easily fixed with glue. There are articles on moulding new ones and at one time someone sold brass replacements. The ones on my 8640A are cracked. I just take it very easy when I use it as I can't face up to replacing them.

That can be fixed more or less with very fine steel wire mesh.  Cut it so it has the shape of a half moon and then apply it after heating it to red to the flat side of the gear so that it melts enough to get inside the plastic. The trick is finding this fine wire mesh, I do repair lots of cracked plastic this way

[Zenith]

That's well worth remembering and is a lot better than moulding new gears or getting hold of brass gears. It would be nice to see at least photos of the technique being used, especially with these particular gears.

I find it extremely irritating that they built these fine sig gens, which cost the price of a small house, and cheaped out with nylon gears, rather than use brass for a few bucks more. There and again, I doubt it occurred that they'd still be in use 40 plus years on.