R-390A INTERMITTENT AGC

[W2JBL]

   one of my R-390A's has been driving me nuts with an intermittent AGC problem for a few months. the other day i got bothered enought to troubleshoot it. when the smoke cleared the problem was very easy to repair. this is a nice clean Collins unit that i had recapped a few years ago, and was otherwise 100% and sees a lot of use. ever look at the jumpers on the back of the receiver for remote RF gain and AGC connections? well, i did. seems they grew a bit of corrosion on them, between the disimilar metals in the termial strip, jumper, and screws. now i live in a salt water enviornment so troubles like this tend to hit now and then.  after a rather extended troubleshooting session i landed at that terminal strip and found i was losing AGC right there.  a cleaning of the offending parts with steel wool and a light coat of Hoppe's #9 and i was good to go. this would be a good thing to check before you go nutso recapping etc.

[Chuck_WA4HHG]

AGC problems are the worst.  The AGC line feeds both the IF and RF deck.  Turn the AGC on, turn to a local AM flame thrower an meter the rear AGC jumper to chassis ground. Should be something over 7 volts.

No AGC troubleshooting starts with checking the IF levels at the input to the AGC rectifier and going from there.

Chuck WA4HHG
SKCC #967

   one of my R-390A's has been driving me nuts with an intermittent AGC problem for a few months. the other day i got bothered enought to troubleshoot it. when the smoke cleared the problem was very easy to repair. this is a nice clean Collins unit that i had recapped