[R-390] R-390A Conversion Oscillator Low output

[Perry Sandeen]

Yo Bubba Dudes!,
Sometimes one can spend large amounts of time trouble shooting a circuit to no avail as everything seems to check out OK
IF all the voltages check out and connections have been re-checked for mechanical integrity it might be a good time to *Shotgun* the circuit by just replacing all the components in the vicinity.
This is not a substitute for good trouble shooting.  If practical having a friend review what you've done and the *Oh my goodness* moment arrives where one finds something, perhaps obvious that was overlooked. And it's embarrassing.  But we've all done it and it's just a fact of life, so we try to shrug it off (sometimes with difficulty) but we've learned a valuable lessen (hopefully).
That all said, with a radio whose OEM parts qualify for Social Security,  The *shotgun* method is not unreasonable.  There have been times in the past where I've done it and the problem is solved. Yet each part tested OK. You end up scratching your head and look for a cold 807.


With OEM parts this old although they test OK with the test equipment we have, just fail somehow in the active circuit and we'll never know what it is.

Because of the large amount of capacitors that have proven to be problems as noted on the Almost Ultimate R390A schematic, I'm an advocate of replacing all the caps, including micas as it not a matter of if, but when. I also advocate replacing all the carbon comps with 1% metal films which aren't all that expensive if one shops around as there are many used of the same value.

I'm not advocating that you take a perfectly good A that meets all its specs and take it apart.It is when you have ongoing repair problems, or the receiver just can't make specs no matter how you swap or replace tubes, then this is a good sign that a reman is a good idea.

Now if you do this, ONLY do one section of module at a time. For if one was to make two or three errors doing the replacement you could go nuts trying to find the errors. As signals go back and forth to the modules, an error that shows up in one module is really in another.

Additionally if you do this slowly over a time span its far less stressful and the chances of errors greatly diminish.  I've found this out more than once on the late friday or saturday nite at zero dark thirty in the AM where it was *just one more* whatever  Lost sleep, got up late the next day not refreshed and generally had a lousy day.

Now some receives are going to need it sooner than later as some were used without good cooling care.  So it becomes some what of a crap shoot to when to reman, but it always will come.
Regards,
Perrier