[R-390] Detector tests followup

[n4buq at knology.net]

On Wed, 20 Sep 2006 07:59:39 -0500, "Cecil Acuff" <chacuff at cableone.net> 
wrote :

> Need to try that same test and back up to pin 1 on T503.  If .33V at that 
> point gives you proper level at Pin 7 of V507 then the problem is either 
in 
> T503 or a bad V506 the 5814/12AU7. (swap it with V206 out of the 
calibrator 
> for a test)

Inserted the 0.33V audio on pin 1 of T503 and got the desired reading.  
Hmmm.
> 
> Check for a 6 ohm reading across pins 1 and 2 of T503 and an open circuit 
> between pins 1 and/or 2 and the remaining pins of T503.  It's possible 
L513 
> in T503 could be open...or shorted to a turn of L512.

Checked 6 ohms for both windings; however, I don't get infinity between 
coils when the deck is connected to the main harness.  If I disconnect the 
diode load, the windings show infinity between them so something downstream 
of the diode load is providing a high-resistance between the windings 
(about 50k).  I notice this varies a bit when turning on/off the limiter.  
Perhaps the circuit ties back from the centertap of the primary back to the 
limiter.  I briefly looked into that but was on my lunch break and didn't 
look at all the places where this could provide a high-resistance shunt 
between the primary and secondary windings.

> 
> As a long shot you could lift one end of C535 and see if isolating the 
BFO 
> circuitry has any effect.
> 

One interesting thing about the BFO.  With it off, there is very, very 
little no-signal noise.  With it on, the no-signal noise jumps up 
dramatically.  Don't know what this has to do with anything but thought I'd 
mention it.  It's one of the main things that made me start trying to 
diagnose this deck.

> Getting close...
> 
> Cecil...

Thanks again!

Barry - N4BUQ