[R-390] 390A help...

David Wise [email protected]
Mon, 15 Apr 2002 13:36:38 -0700


> From: Fabio Liberatori [mailto:[email protected]]
> 
>     Hello,
>           we have a 390A with a particular problem : it doesn't work 
> on the first part of ANY MHz, say about the first 80/120 KHz, then 
> when you go over this point it start to work...
> 
> If we increase a bit the AC voltage power on the Variac, this 
> receiver starts to work after the first 60 KHz (instead of first 
> 80/120 KHz) : this is an interesting point for your ideas about this 
> troubleshooting...

My main guess is the VFO.  First, here is a simple test.
This will tell whether it is the VFO, or something else.

1. Put a second shortwave radio with antenna near V701.
2. Tune the second radio to 2455.
3. Tune the R-390A KC dial to +000.  The second radio should
   "hear" the R-390A's VFO.
4. Tune the second radio to 3455.
5. Tune the R-390A KC to 000.  The second radio should
   hear the R-390A again.  If it does not, the trouble
   is definitely the VFO, and you can concentrate on it.

You could also do the Oscillator Injection Voltage tests
from the R-390A manual, section 5.5.3 .

If you have found that the VFO is bad, test V701.
If it's ok, measure the voltages on V701.
If RT510 is a 3TF7 as it should be, V701 heater
should be 6.3VAC.  Plate should be around 200,
and screen grid should be around 60.

Let us know how it goes,
Dave Wise