[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