[time-nuts] HP-3336A - High Precision Attenuator

[Rex]

On Tue, 17 Jul 2007 08:42:56 -0700 (PDT), Tom Clifton <kc0vsj at yahoo.com>
wrote:

>Greg Burnett hit the nail on the head. It  is a
>machined base with four solenoids.  I'm a bit hesitant
>to start taking screws out of it as I'm not sure what
>holds what together... Though if it is dead, what
>additional harm can I do...
>
>Any waym the assembly seems to have an HP part number
>of 1979a - anybody ahve a schematic on either the high
>precision attenuator for the 3336a or something on the
>HP part number 1979a?  
>
>I have photo's I can email if it would help.
>
>Tom in St. Louis
>

Maybe I can help with a drawing I made, if it happens to be the same
design.

Some years ago, I crossed paths with an 8350 RF Synthesizer. The RF
module in it had a problem with setting the output level consistently.
Going up and down at some dB output boundary, sometimes the value was
good and sometimes it was off. 

I opened the unit up, found the output attenuator, and was able to open
that and clean it. Fixed the problem for at least the week I had it.

I made a hand drawing of what was in there, thinking it may come up
again. 
Posted here: ftp://ftp.sonic.net/pub/users/rexa/HP_atten/HP_attenuat.gif
My notes on the drawing says it is similar to 8494/95/96 attenuators.
These are small HP bench attenuators that can be either manual (knob),
or electronic controlled. I have a manual version labeled 5086-7362. I
can't remember; I may have opened it up first before I had the courage
to try the one in the 8350 RF unit.

The one shown/described has 3 sections. Sounds like one in your unit has
4 sections. Maybe the design is the same.

The parts inside are small and delicate, but I don't remember any major
danger of breaking things when I opened it. I don't think I did anything
on the actuator side, though.

As you can see from the drawing, there is a channel down the middle, the
geometry of which, I'm sure, maintains the impedance. On one side of the
channel, are 3 attenuator sections on substrates. On the other side are
3 gold plated straight trace sections. 3 metal spring sections are
deflected to connect-in either the attenuator or the straight conductor.
Each actuator (solenoid for electronic, or cam for manual) moves two
pins to force adjacent ends of metal strips onto an attenuator. In the
deactivated position, the pins are relaxed and the metal strips bend to
the straight-through sections.

I gently cleaned the spring contacts and connector portions of the
attenuators and through-strips. Can't remember what I used as a cleaning
tool, maybe small strips of paper, maybe toothpicks. I think I used a
small amount of alcohol or acetone.

So my assault on the guts of the attenuator turned out successful, but
use this information at your own risk. Some testing first to decide
which atten increment change is behaving badly might help focus on which
switch connections may have problems.

Hope it helps.

-Rex