Also shoot some contact cleaner into the AGC toggle switch.
73,
Bob WB2VUF
Dr. Gerald N. Johnson wrote:
> 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
>
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>
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