[R-390] IF Deck Revisited (Revisited)

[n4buq at knology.net]

Since I'm having several issues with the IF deck, I made a geniune effort 
to check resistances and voltages on all tube pins in the IF deck.  This 
time, I recorded all the findings along with their spec'd values so I can 
refer to that list for places to check.  Most things were fine, but there 
are some grids with positive values where they should be negative, etc., so 
I'll begin there.  The first thing will most likely be to try new/different 
tubes in some of those positions as I assume grid emmissions could be a 
problem for symptoms like that.

One problem I'm having is when I switch from MGC to AGC, the carrier-level 
meter jumps up 20dB and stays there.  I found the cathode resistor on V506A 
(R548) to be about 41-ohms instead of 27.  I don't have a replacement, but 
I put a 100-ohm resistor in parallel which should bring it down to about 28 
ohms.  The carrier-level meter jumped up somewhat in MGC, but I can re-zero 
it and when I switch to AGC, it still jumps up 20dB so all I did was change 
the reference point.  Not the main problem...

What I'm wondering is a good way to debug this thing.  Is it possible to 
start at the input and work my way forward (or vice-versa) and try to get 
it working properly stage-by-stage?

Thanks guys,

Barry - N4BUQ (the other, other Barry)

PS: As a side note, now that I have new probe points, I used my HP-410B for 
both resistance and voltage measurements.  I've usually used the DVM for 
resistances because it was a pain to keep switching the pin between the 
probes.  That sure is nice to use a real meter to check resistances!