[R-390] A bit more on my IF deck

[n4buq at knology.net]

Okay, more ramblings.

Tracing Pin "E" on the RF deck, I see a path through L208, R232 (22K), R231 
(1M), through S207 and then through the selected L22*-2 winding to GND.  
Therefore, this places a theoretical 1.022M (not includine the negligible 
coil DC resistances) across the 500K in the IF deck at Pin 2 of V506.  If 
this is true, then doing the math, the reading at Pin 2 of V506 should be 
approximately 335K.  Am I missing something here??

Barry - N4BUQ

> Okay, I think I'm carrying on a conversation with myself here, but I'll 
> continue...
> 
> When I pull the main connector from the IF deck, the resistance at Pin 6 
of 
> V506 goes very close to 500K (what the book says it should be).  If I 
> reconnect the IF connector and unplug the RF deck connector, the same 
> thing: 500K.  So, I checked the resistance at pin "E" of the RF deck (the 
> point where Pin 6 of V506 connects to the RF deck).  I get about 1.8M 
> here.  Those two resistances in parallel yeild what I'm seeing at Pin 6 
of 
> V506 when everything is connected.
> 
> I haven't traced it out, but I assume if I'm supposed to be seeing 500K 
at 
> Pin 6 of V506, then the resistance at Pin "E" on the RF deck should be 
> nearly infinite.  Any comments on this?
> 
> Barry - N4BUQ
> 
> > I got the resistors replaced and all seems fine.  I need to do a full IF
> > alignment, but it seems to be behaving just a slight bit better.  I'm 
not
> > sure, but I think it doesn't take quite as long for the system to dump 
the
> > charge from SLOW AGC as it did.  Is that perhaps a function of that 2.7M
> > resistor?
> > 
> > I wanted to check the resistances and voltages around where I had 
worked.
> > Everything looks pretty good except for pin 2 of V506.  According to the
> > manual, I should have about -0.4V, but I'm getting nothing (HP410B used
> > here).  Checking the resistance, the manual states I should be seeing 
500K
> > in AGC mode and I'm only seeing 400K here.  There are three resistors 
to 
> GND
> > from V506, pin 2 and they add up to 500K.  Apparently I have something 
> else
> > parallel to this that's pulling the resistance down a bit.  It's always
> > something.  Any guesses why I don't see -0.4V here?
> > 
> > Thanks,
> > 
> > Barry - N4BUQ
> > 
> > _____________________________________________________________
> > R-390 mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/r-390
> > Help: http://mailman.qth.net/faq.htm
> > Post: mailto:R-390 at mailman.qth.net
> > Unsubscribe: http://mailman.qth.net/mailman/options/r-390
> > 
> > 
> > 
> _____________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/faq.htm
> Post: mailto:R-390 at mailman.qth.net
> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
> 
> 
>