[R-390] Gain drift

[Roy Morgan]

> On Oct 19, 2018, at 11:15 AM, dog <agfa at hughes.net <mailto:agfa at hughes.net>> wrote:
> 
> Interesting. I disconnect TB102, 3-4, ground 4 and 3mV into J513 is way too much RF for the carrier meter in AGC mode. Reduce the input to about 250uV and that gives me 50 on the carrier. 0V on TB102-3. About 5 minutes later the carrier drops to 0. I have to increase the RF input to 1.3mV to get 50 on the carrier again.

I suspect you have an intermittent capacitor or coil in the RF system.  

Insert the RF signal into the various test points in the RF deck.  Look for the table of voltages (they will be APPROXIMATE) for the various stages (and appropriate frequencies).

I assume you have ruled out the IF deck with an IF signal at it’s input - and perhaps set the IF gain while doing that.

Roy

Roy Morgan
k1lky68 at gmail.com <mailto:k1lky68 at gmail.com>