[Boatanchors] DM-28 Dynamotor Restoration Questions

whitebear1122 at comcast.net whitebear1122 at comcast.net
Wed Apr 8 10:06:09 EDT 2020


Here is an update on the DM28 repair.  I was able to successfully repair the
broken brush assembly.  In spite of being so careful when removing it, the
brush wire broke right at the brush, leaving a tiny nubbin of wire.  On
closer inspection there was a small blob of loose hard plastic like material
over the wire where it attaches to the brush.  Possible a strain relief.  I
clipped away a small amount of the material to reveal a bit more wire. I
soldered a piece of flexible 'solder wick' to the nubbin and then the
remaining original wire to the solder wick.  I needed to compress the spring
in order to do the soldering.  I came up with this 'great idea' of using a
sewing needle and thread, manually compressing the spring, then running the
needle and thread through the center of the compressed spring many times
until it stayed tightly closed.  By golly it worked.  I slipped this now
tiny spring over the wires, did the soldering, then cut the thread away and
the spring released to normal size.  Nice when something crazy like that
works out.

I put the dynamotor back together, loaded the brushes, and fired it up with
a switching power supply.  The dynamotor actually worked.  That was a
surprise also.  My expectations are so darn low that anything good is a
surprise :)  I was measuring around 217 volts DC.  

Now that the dynamotor is running, I didn't realize just how noisy they are.
While it might have been fine for the B17 Radioman since he couldn't hear
the dynamotor whine over the noise of the engines, it would drive me nutso I
think in the shack :)   I think I'll make an external supply for it.

I found the replacement film capacitors and plan to start recapping today.
73, Scott WA9WFA




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