[R-390] Fixing a R-390A module connector

[David Olean]

Here are some shrunken down pictures of the busted R-390A pin repair.  
When I tried taking the IF deck out to clean it and replace the Vitamin 
Q filter capacitor, I was horrified to see one of those pins flattened 
down against the chassis. It broke off as soon as I touched it.

Here is a photo of the missing pin. There is enuf meat in the connector 
pin base to drill in about 0.100" without messing anything up. The hard 
part is getting a drill bit started, so I filed down what was left where 
the pin broke off and then gently ( so I did not break the connector 
body)  used a prick punch to make a dimple to locate a small drill bit 
in the middle of the brass. I used a hand held pin vise and twisted it 
with a very small (#66)drill bit to get the hole started.  Once I had a 
small indentation, I used my drill press and a #66 drill bit to drill 
the hole.

Once I got it drilled to about 0.10" deep, I used a #60 bit to open up 
the hole to 0.040" which is the diameter of the brass pins in the 
connector.  Note that I have the IF assembly bolted down to the drill 
press so it won't move!


The completed job with the new brass pin. I rounded off the top to match 
the others. It might be possible to find some 0.040" brass wire so you 
don't have to make your own.

I just finished working on an old R-390/URR from the original Collins 
order in 1951.  It was in rough shape with regulator problems.The 
regulator was pumping out almost 300 volts instead of 180 volts, so all 
the surge resistors were cooked. I found a man made short inside where a 
bare lead on a capacitor was shoved into another component!  After 
fixing that, it regulated at 220 volts because of overheated parts in 
the VR tube chain.  I got it working fine after some more new resistors 
went in.  More cleaning and tweaking and a full alignment produced some 
really good sensitivity numbers. I am seeing 0.14 microvolts AM 
sensitivity in a 2 kHz bandwidth.  Most of my problems were in the 
Crystal deck with bad connections on the switch positions. It would make 
the oscillator develop output at twice the crystal frequency since the 
tuning capacitors were not making contact to resonate the output coil. 
That caused very poor LO injection amounts and poor sensitivity. It took 
awhile to get the switch to clean itself up. It is now working just fine 
on all bands.

One thing I noticed is that all of the crystals in the 390/URR do not 
show much aging even though they are 68 years old. They are all just 
about spot on!  The PTO was way out at 7.5 kHz and no more room for 
adjustment, so I removed a turn from the end point coil and got it 
working again within a few hundred cycles.  The R-390 is a joy to use, 
but you all know that!

I could very easily be persuaded to fix broken pins on these module 
connectors. I would not even try it without a drill press. You need 
precise control of the drill bit or the small sizes are easily broken.  
I should look around for some 0.040" brass wire. That would make the job 
much easier than rolling your own on a lathe.

Dave K1WHS