[R-390] Latest R390A Project (long)

[n4buq at knology.net]

I replaced the capacitors and resistors in the IF transformers with little 
(if any) improvement to the IF alignment this last weekend.  I mentioned 
earlier that it appeard one of the slugs was at or near it end of travel 
before I got to the peak point.  Thinking it could be an out-of-tolerance 
capacitor(s), I replaced them.  After replacing these components, the slug 
peaked in about the same position as before.  Determined, I cranked down on 
it just a bit harder and noticed the coil form was turning just a bit.  
Fortunately, there is sufficient slack in the Litz wires so they weren't 
damaged.  I epoxied both of the coil forms in T501 and T502 so they 
shouldn't be going anywhere soon.  I can crank the slug sufficiently now to 
get to both "sides" of the peak so it looks like I'm "done" in that area.  
Still can't stagger-tune the thing, though.

I did notice I got a much strong Diode Load reading when in the 2kc 
position as opposed to the other filter settings.  Turned out that the 
lower trimmer caps were way out of position.  After setting them, the 
various filters now have close to the same Diode Load reading.  There's a 
little variation, but I assume that's expected as each filter ages 
differently.

I then started looking at the AGC action.  I've mentioned before that SLOW 
AGC produces an increase in gain than the other AGC settings.  I hooked the 
scope to the IF output and monitored it in all three settings.  The MED and 
FAST settings seem to keep the IF output level fairly close to the same 
values when receiving a strong station.  Switching to SLOW causes the IF 
voltages to increase substantially (maybe a factor of 3 or 4 times that of 
MED or FAST).  It seems to distort just a little on SLOW mode as well, 
particularly on strong BC stations.

I then watched the AGC voltages last night.  All three postitions yield 
very close to the same value (about -2.5V if I recall correctly).  
Switching to AGC causes the voltage to climb nicely to that point.  If I 
switch from FAST to MED, the voltage stays nearly the same level.  
Switching from MED to SLOW causes the AGC voltage to drop considerably 
(nearly zero) and slowly climb back to -2.5V (assumably as the 2uF cap 
charges).  Switching from SLOW to MED or FAST causes the AGC voltage to 
spike as the cap discharges and then the voltage settles back to -2.5V.

I would think the AGC voltage action above seems normal, yet I'm getting 
the distortion on SLOW AGC with the IF output being too high in that 
postition.  Any ideas what might be wrong?  I assume this isn't the correct 
behavior.

Thanks!

Barry - N4BUQ