[R-390] R390A 2nd osc. hot R406, R407

[Charles Steinmetz]

Roger wrote:

>So once upon a time V401 went short and the resistors got burnt.
>The tube got replaced.
>The receiver worked OK
>and things were left.
>
>You found some parts that had long ago been stressed.

I guess I wasn't as clear as I had hoped!  I don't think V401 had 
anything to do with it -- its cathode couldn't boil off electrons 
fast enough to cook R406 and 407, under any circumstances.

I think the problem is one or more leaky capacitors attached to 
S402.  Most likely, one or more of the fixed capacitors C417 through 
C428, but possibly one or more of the variable trimmers.  I suspect 
the problem cap(s) is (are) still there.  Of course, they don't 
actually draw excessive current until you switch to the band(s) with 
the bad cap(s).  If you're lucky, the oscillator won't work on that 
band(s) and you'll know something is wrong.  But I wouldn't bet on that.

This actually could be one of those rare occasions when it is wise to 
replace more than just the bad component.  If one or more of the S402 
caps is bad, it is likely due to environmental conditions -- in which 
case, they may all be at risk.  So, once you find one bad cap 
attached to S402 (BUT NOT BEFORE -- don't shotgun without 
troubleshooting), you might want to consider replacing them all.

Best regards,

Charles