[ICOM] 751A Transmit

[Gary P. Fiber]

My guess the RF board is causing some oscillation. In the past its 
generally been one of the TR switching transistors causing it. You might 
pull the receiver cable to the RF unit and see if the uncontrolled 
output stops.

Gary K8IZ

Paul Gates, KD3JF wrote:
> How do you think this all came about?
> Paul KD3JF
>
> EP Swynar <gswynar at durham.net> wrote: Good Day All,
>
> My venerable 751A put up some very strange behaviour yesterday, after having sat idle for some 3 months...I wonder if anyone reading this might have a suggestion, or two, before I open the rig up later this afternoon? Any & all feedback / comments are not only welcomed, they're hereby being solicited! Hi Hi
>
> Specifically, I fired up the rig to transmit on 40-meters and the power output meter showed nearly 150-watts! I reduced the drive control COMPLETELY counterclockwise, & it STILL put out the same power...
>
> The carrier would stay continuously "on", too, dropping off ONLY when the VOX did. 
>
> This strange condition was evident on both a dummy load, as well as a resonant antenna. All "peripherals" were removed, the grounding was checked --- status unchanged. I tried it on different bands, but the only difference was the power output, which varied from 100- to 150-watts (dependent upon the band). 
>
> Finally, I tried 10-meters & the output suddenly dropped right off to zero --- I'm sure I popped the internal fuse with that last test.
>
> It would appear that the finals in the rig are somehow "taking off" / self-oscillating, for some reason. I have not touched the rig in any way, shape, or form, since QRN took over 160-meters here last April.
>
> I wonder if, by sitting idle like that, one of the interior connectors has somehow oxidized / deteriorated in the humidity of summer...?
>
> In any event, I have to get inside to replace the fuse anyway, so I'll check those out...but I am curious if anyone else has ever had any similar such occurance with their 751A...
>
> Thanks in advance, & vy
>
> ~73~ Eddy VE3CUI - VE3XZ
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
>
> .
>
>