Louie: While John is correct when he says proper improper operating
procedures can result in these problems, the 781 is known to have had
internal ALC circuitry problems that caused a leading spike to be generated.
Some 781s were produced with an electrolytic capacitor installed in the
wrong polarity, and some had component values installed that did not match
the original schematic. There was also a problem with a resistor value on
the power supply board being incorrect, resulting in a voltage used in the
ALC circuitry being too low. After I made the recommended changes, the
leading spike was no longer a problem. Those who had contacted Icom over
the years regarding these problems received similar responses - "that's the
way things work and nothing can be done to fix it". In fact, when all
components were installed to match the schematic and the supply voltages
were correct, the problem was fixed. This problem also existed in earlier
775s, and I've never seen any documentation indicating a solution had been
found there. On the other hand, other Icom rigs I've owned, including the
765 and 746 did not exhibit the leading spike problem.
I suspect that John is referring to the setting of the Drive and Power
controls possibly being the cause of a similar problem. If one sets these
too high, depending upon the ALC to limit the power from the transceiver, it
makes sense that a spike could occur owing to the response times of the ALC
circuitry in the amp and transceiver.
73, Floyd - K8AC
----- Original Message -----
From: <Gudguyham@aol.com>
To: <shr@swtexas.net>; <desk@nwlink.com>; <amps@contesting.com>
Sent: Tuesday, October 11, 2005 9:13 AM
Subject: Re: [Amps] alpha 87a and Pro II question
> Jon, I believe that is was in fact a 781 that my buddies were having
> problems with in this regard. PLEASE....You mention about reading the
> manual and
> fixing the problem, Since I don't own an ICOM radio or manual and the
> poster
> with the problem may not have one either....can you tell us what in the
> manual
> tune up procedure makes this problem go away. I am curious to know what
> resolves this problem. Louie
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
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