[R-390] new member, R390A, no signal when first powered on, works after 10min but RF cutting in and out

[Scott Overstreet]

I'll bet on a dirty tube socket.

Take all the tube shields off and turn on the power from a cold start.

Wait 30 seconds or so until the radio would normally come to life and 
then work each tube in it's socket "round and round" (circular motion) 
using the tube top tit as a handle. This will move each pin up and down 
in the socket while you listen for effects. If you find a bad one, keep 
up the circular motion---eventually the bad connection will cleanup. 
Don't stop if the radio comes to life as you describe---chances are that 
wiggling the connection that fixed itself will still ID itself.

I say a tube socket because your time after turn-on is quite short which 
suggest to me a short thermal path like a tube pin to socket 
problem----but whatever the problem is, it is thermal warm-up related. 
The problem might be a bad solder joint on a tube socket and if so, the 
move the tubes in their sockets will fined it.

If the above doesn't fine the problem----jiggle everything using a stick 
where necessary to stay clear of HV.places.

Scott, N6NXI



On 6/26/2014 12:14 PM, weekspat at imonmail.com wrote:
> Hi,
>
> I got a Motorola R390A, signal corps unit last year.  Have recapped,
> and fixed most problems, but I've got one nasty intermittent one.
>   Seems like the RF signal is not getting to the RF AMP and or
> conveter or thru it, so I think I've got no signal to the IF section.
>   Then after some time it starts making some popping sounds and
> shortly after that "pops" on with normal reception.  Happens on all
> bands.  I'm wondering if those mini BNCs are to blame.  Any hints ?
>   The problem sort of " comes and goes" so its hard to nail down
> thanks, Pat Weeks
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