[R-390] Detector tests followup

[n4buq at knology.net]

On Tue, 19 Sep 2006 12:56:11 -0500, "Cecil Acuff" <chacuff at cableone.net> 
wrote :

> Did you record the signal level required at terminal 15 to get the .15v 
at 
> pin 7 of V507?  Just curious whether it took just a bit more level or 
> something closer to 4v p-p.
> 

I don't recall the value at terminal 15 to get 0.15V at pin 7, but I'm 
pretty sure it wasn't anywhere near 4V - perhaps something nearer 0.3V - 
0.4V.  It seemed about right to compensate for the series grid resistor.

> Simple test for C530....cut one end of it loose but where you can solder 
it 
> back.  See if that brings the signal level up.  C530 and L502 are used to 
> remove the 455kc signal from the audio...
> 

I can certainly try that.


> It could also be a bad T503 secondary or C562.  Pull the cover off T503 
and 
> inject your AUDIO signal into pin 1 of  T503 with the diode load jumper 
back 
> in place and see what you get.
> 

Okay.  Something I just noticed about the schematic versus my IF deck: the 
schematic shows RCL on each side of the IF transformers whereas (and my 
memory might be playing tricks on me here) my transformers have two 
capacitors on both the primary and secondary of the transformer (in 
addition to the resistor).  I wonder if this was a "tuning" thing.  It 
appears to be factory but maybe not...

> I would also do a continuity test of the cable from terminal 14 back to 
pin 
> 1 of T503 and center to ground etc....
> 
> One thing that don't add up is that you were originally injecting .1V at 
> Pins 6,7 of V506B and expecting to see the equivalent of .15v of audio at 
> Pin 7 of V507 where you just had to crank the level going in at the diode 
> load point to achieve .15 volts of signal at Pin 7 of V507.  Those number 
> don't add up.  Where did you get the .1V of 455kc at the plate of V506B 
> from...out of the manual somewhere?  My manual is showing a level of .3 
to 
> .4 V at pin 1  (grid) of the 4th IF amp V504.  I don't see anything 
showing 
> the expected output on of that IF amp is but I would expect it to be 
fairly 
> high to drive a decent signal through T503.

That value came from the Y2K manual in one of the trouble-shooting tables 
(chapter 5 I believe it is).  It is a step-by-step trouble-isolating 
procedure that starts at the audio deck and works its way back up the 
chain.  It shows what you should see for various signals injected at 
various points in the various decks.

> I haven't found any expected 
> level at the input of the detector so far....but something approaching 1 
> volt p-p might not be unreasonable.....100mv sounds low but I haven't 
> measured a working radio that I remember.  The signal substitution 
process 
> in my manual speaks only in general terms as to the levels to inject in 
this 
> area...things like sufficient signal level to achieve an output etc....
> 
> Cecil....
> 
>

Thanks!

Barry - N4BUQ