[ICOM] IC781 Tx problem

[Larry Benko]

Paul,

I don't agree with your statement. I  have made several measurements on 
the keying of Icom radios and the "hsend" line is timed extremely close 
to the reed relay output.  Since Icom radios don't have any menu 
adjustments for amplifier timing something must be amiss if your 
measurements don't match mine.  Please take a look at  
http://www.bnk.com/w0qe/amplifier_timing.html for my measurements.  I 
have seen the symptom that was mentioned but it was fixed by a good 
common mode choke going to the Acc jack on the Icom radio.

73,
Larry, W0QE

Paul Playford wrote:
> I had a similar problem with my PROII when using the keying lead on 
> the din connector (instead of the RCA connector relay output) to put 
> my Alpha in the transmit mode.
>
> The signal on the din keying lead appears after transmit rf is being 
> generated (cw), which meant the PROII was transmitting into an open 
> circuit (while the antenna relay in the Alpha was switching), 
> resulting in a high swr that caused the PROII's swr detection 
> circuitry to shut the transmitter down with a slow recovery to full 
> power output.
>
> Easy to check: connect a dummy load directly to the RF spigit on your 
> 781.
>
> de Paul, W8AEF
>
> ZF2JL/ZF2TA  FO8DX/FO8PLA  8Q7AA  XZ0A  VU7RG  TX5C
>
>
>
> ----- Original Message ----- From: "Jaime Gomez" <jgomez2005 at gmail.com>
> To: "ICOM Reflector" <icom at mailman.qth.net>
> Sent: Thursday, December 11, 2008 17:54
> Subject: [ICOM] IC781 Tx problem
>
>
>> I still have the problem in Tx with my 781. I rebuilt the ALC circuit 
>> as per
>> K1FV corrections, but the problem still remains. The DC Tx voltage is
>> turning OK (No delay at all) when I operate the send switch, but the
>> carrier, no matter what mode, power or band I am using is delaying 
>> about 2
>> to 3 seconds before it gets to full power output. The power control is
>> working OK once I have carrier, so I doubt it can be. I have checked 
>> all the
>> DC voltages and are OK, I can see (with my scope) the problem in the 
>> RF IF
>> signal out from the IF board. Anybody has experienced something like 
>> this?
>> Any hint? I really appreciate any help. It is impossible for me to 
>> send it
>> back to US for repair,
>>
>> Jim, HK1N
>>
> ----
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