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

[David Olean]

I guess the pix did not go thru. They were 640 x 480. I guess they must 
get smaller.(?)

Dave K1WHS

On 10/19/2019 11:25 PM, David Olean wrote:
> 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
>
>
>
>
>
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