[ICOM] 751A Transmit

[Clif Holland]

You have a leaky diode and/or cap on the RF unit causing feedback. If you 
unplug the RX jumper it will quit.

Clif Holland KA5IPF
www.avvid.com




----- Original Message ----- 
From: "EP Swynar" <gswynar at durham.net>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Tuesday, July 24, 2007 6:34 AM
Subject: [ICOM] 751A Transmit


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
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