[R-390] R390A not working at all

[Tim Shoppa]

Kurt Schabel asked:

> Some years ago I had bought a deffective R390 A
> receiver, all tubes were checked but it does not
> receive any signal. All voltages seemed to be ok 
> too. The problem is probably in the front end,
> which I had already dissasembled  and check
> some resistors and capacitors. Does anyone had a
> procedure to verify the trouble with the front end of the 
> radio out?

The Y2K has an official diagnostic procedure.

Signal generator of any kind (even just the ones that
make a raspy square wave all over the spectrum) will
put you far far ahead of where you are now.

Start injecting at the audio stage and
work your way back
until you don't hear the hash anymore.

If your signal generator happens to do IF frequencies
(e.g. 455kc) in partcular, even better.

Lacking a signal generator, knowing what noise
from different stages (audio, 455kc IF, other
IF's) sounds like would help you.

"Completely dead"
as you describe it (no hum, no nosie anywhere)
would have you starting at the audio stage, not
the RF amp.

If you are getting some noise, starting at the
AF and pulling/re-inserting tubes will help
you find where things are stopping.

A simple coil on the end of a scope probe will
help you determine that the oscillators and
bandswitch are doing their stuff. You should
see the PTO freq, the 17 Mc freq in the
back corner going on/off at 8Mc on the Mc
tuning knob, the correct frequencies for
the 32 band at the main crystal oscillator
bank, as you move the sniffer around.

Checking the 17Mc oscillator going on/off
at 8Mc is a very quick sanity check for
massive misalignment of bandswitch. (But
not a complete check.)

Turning the bandwidth knob with a 
failed mech filter coupling capacitor will
wreck all your mech filters instead
of just one, BTW :-(. 

Tim.