[R-390] AGC investigation, one very bad part

[David Wise]

Ha!  Nailed it.  Good job, Alan!

Dave Wise
________________________________________
From: R-390 [r-390-bounces at mailman.qth.net] On Behalf Of Craig Heaton [hamfish at efn.org]
Sent: Thursday, October 09, 2014 7:30 PM
To: 'Alan Victor'; r-390 at mailman.qth.net
Subject: Re: [R-390] AGC investigation, one very bad part

Alan,

Sounds like your off to the races! There were a few resistors in the IF deck
where I had to unsolder one end to get a correct reading. At my age, lucky
to remember "had to unsolder one end", which resistor(s), who knows.

If the receiver has been sitting in the barn for a few years, yes there will
be mechanical issues. Elbow grease will fix those.

Craig,

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Alan Victor
Sent: Thursday, October 09, 2014 6:58 PM
To: r-390 at mailman.qth.net
Subject: [R-390] AGC investigation, one very bad part

After looking at the open AGC loop behaviour and the schematic, it became
clear something is wrong in the bias string setting up the AGC reference
voltages. That coupled with some resistance measurements leads to *R544*.
Its value nominal is *2.7 Meg*, measured *327 K*.

This really upsets this string bias current, the voltage divider and the
subsequent AGC voltage points when the loop is   closed. I'm sure there are
more culprits, but for now its electrical is reasoanable. There are now more
mechanical issues then electrical,  so a clean up is in the works.

Thanks,
Alan W4AMV.