[R-390] AGC Troubleshooting

[Dennis L. Wade]

Good afternoon,

	Got some time to look into the AGC trouble in my Motorola R-390A. 
First thing I wanted to do is satisfy myself that there was indeed a 
problem.  I looked at the AGC line with a strong signal and the 
Calibrate sig.  The most I could get was about -4.9 volts at the AGC 
jumper.  Under no signal conditions the AGC line is about +0.15

	I then took the HP-410C and looked at resistance.  From the jumper to 
ground, I see about 350K to 400K with a strong capacitor charging 
characteristic (i.e. much lower resistance rising as something charges). 
  Unplugging the RF deck doesn't change that, unplugging he IF deck I 
get a steady 1.8 meg to ground from the jumper.  I took out the IF deck 
and measured resistance from pin 6 to ground, and I see about 7 meg with 
no charging behavior.  Looking at the Pearls of Wisdom, it says I should 
see infinite resistance.

	Looking at the schematic I see the three capacitors AGC line to ground 
in the 1st, 2nd and 3rd if amps (C502, C512 and C519).  These seem prime 
suspects to me.  Do you all agree, and any other components I should 
look at?

	I didn't take any voltage measurements since the 7 pin extender socket 
I thought I had is actually a 9 pin. :/.

                 Thanks for any help.

                      Dennis

	
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Dennis L. Wade
KG6ZI
Carmichael, CA