[1000mp] New Owner - Help Sought

[Mark G0MGX]

Hi again

I have looked at the AGC components and the **look** intact and I can 
measure directivity in the two switching diodes D2012 and D2013.

I have investigated further on the RF-Board, here's what I have found:

 1. The main RX feed is mixed with the 1st LO and fed out of J1012.
 2. The sub RX feed is pre LO mix and is fed from J1010.
 3. If I stick my scope probe on the inner lead of the cable plugged
    into J2012 that feeds the main RX there is a significant increase in
    RX noise on the main receiver.
 4. I can measure the 1st LO at 70.x MHz going into the connector J1011.
 5. The 1st LO and the signal that also goes to the sub RX are mixed
    with Q1010-Q1013 and then amplified by Q1014. Because these
    components are on the underside of the board I cannot access to
    check signals.

I would like to inject a signal into the antenna socket but I am not 
sure how to safely achieve this with a signal generator? I would need 
about 90uV? What's the equivalent dBm?

I think that the fault is in the 1st Mixer/1st IF circuit before the 
signal is fed out of J1012.

Anyone agree?

Mark
G0MGX




On 10/10/2013 08:23, Mark G0MGX wrote:
> Hi Chen
>
> Thank you.
>
> The RF gain is fully clockwise, and when you decrease it's setting the 
> S-Meter increases as you would expect(but not before s5 where it's 
> "stuck") .
>
> I will take a look at the AGC part of the circuit and report back.
>
> Mark.
> G0MGX
>
>
> On 10/10/2013 07:39, Kok Chen wrote:
>> On Oct 9, 2013, at 11:29 PM, Mark G0MGX wrote:
>>
>>>   I also see that the S-Meter for the main RX is permanently at 
>>> about S5.
>> Mark,
>>
>> That usually is an indication that the RF gain pot is turned down.  
>> If so, that could also explain why the receiver is moderately deaf.
>>
>> If the pot itself is not physically turned down, you might check the 
>> AGC circuitry to see if something is broken.
>>
>> Vy 73
>> Chen, W7AY
>>
>>
>>
>>
>