Engineer wrote:

We acquired this receiver "new in box", unissued, clean and complete,
with a test report dated "3/2/44" - a good start! Unfortunately, the
"new" Bendix dynamotor type DA-TA is seized up (tried it on a variable
low voltage DC, the current spiked up, no motion, switched off fast!)
It last ran in 1944 and for the last 65 years has been in storage. My
guess is the bearing grease has congealed and/or the brushes have
stuck firmly on the commutators. I just hope there is no rust between
the armature and field core. Is there any expertise, or any
instructions, out there for servicing this unit? If so, I would
really appreciate a few pointers from knowlegeable people. BTW, we'll
be running the radio off external power supplies (app. 250 VDC B+ and
28 VDC for the heaters) but we'd still like the (disconnected)
dynamotor to be servicable.

The big Bendix dynamotors have ball bearings, the little ones have sleeve
bearings. Remove the two screws from each bell end and look inside. You
will soon see what is up.

If they are sleeves or open ball bearings, squirt a little turbine oil
into them and rock the thing back and forth. Check the color of the
oil coming out... if it's not rusty, don't worry about it. Clean the
open ball bearings out with any reasonable polar solvent (even WD-40 is
probably okay) and repack with Mobil 1 Racing Grease or a high stability
instrument grease.

If they are sealed ball bearings, take 'em out and remove the shields
and look inside.

Also, of course, open the brushes and check the brushes to make sure they
aren't stuck.

I have seen dynamotors that looks fine outside but were a solid clot of
rust inside. You'll know when you pull the ends and look inside.

Another thing: the band switch is motor driven. I've not checked this
as we have not yet wired in the tuning unit, but it crossed my mind
that this motor, too, could be seized. Can the band switch be
operated manually (case open, of course), or, if motor OK, by a simple
external switch (I can probably figure the latter out.)

Yup. I'd also check all the paper capacitors for leakage before applying
actual power to the receiver.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."