[TenTec] Corsair II AGC issues

[Dr. Gerald N. Johnson]

On Fri, 2008-02-08 at 20:51 -0500, Dave Perrin wrote:
> Hi-
>  I have a Ten Tec Corsair II that has some AGC and S meter problems:
>   AGC toggle switch has no effect at off or slow. At fast it will cycle from no signal to pinned S meter then de-sensed fully and repeat at 5 second intervals with a strong signal. Distorted audio with the same strong signal input.

Its audio derived AGC, so the time constants have to be a bit longer and
the capacitors bigger. Check electrolytic capacitors on the IF/AF board
for being open or having a high power factor. Replace them with low ESR
types from Mouser.

>  On the IF/AF board, number 80984- the 10K pot labeled R1 on the board looks like R59 on the schematic. It should adjust the S meter. The pot. is located on the board about half way across and away from the front panel on the bottom of the rig. On the schematic it is located near the left edge and midway up the schematic. The part measures about 8 Volts on all terminals. It also measures the variable resistance that it should. It has no effect  when adjusted fully. 
>  I wonder if different rigs may have different IF/AF boards with different schematics relative to manufacturing dates. Mine is 02739.
> 
Could be. I'd believe the single pot near connector 46 is the s-meter
pot. The other two set CW side pitch and amplitude. There is a 10K fixed
resistor R1 in my schematic that could be close to the pot R59.

The meter switch can't be in the IC position to read on receive. So that
might explain the same voltage on both ends of the s-meter pot.

AGC is derived by some op amps and detected by D6 through D9. Its turned
off by Q7 or the front panel switch. Time constants are set by C32 and
C33.

Open connections on these insulation displacing connectors used for the
interconnects are not rare. Nor are opens between the connectors and the
PC board pins. And many board grounds depend on the board mounting
screws where the pressure gets relaxed because the plastic PC board
material lives up to its name and flows under pressure to relieve the
pressure. Clean the connections with DeoxIT and tighten the board
mounting screws.

>  Any ideas or suggestions?
> 
> 73 de Dave in NH

73, Jerry, K0CQ