Excellent response. Just so people won't continue blaming the amp, I had the
same problem with a Kenwood TS-950SDX. At the end of this message is an old
post to AMPS from Dick Erhorn that provides more detail on the problem.
Unfortunately, there's a bug in the 87A's firmware that causes it to report
fault 17 ("abnormal gain") when it gets a leading edge spike. It should be
reporting the "drive too high" fault, but it happens to check for abnormal
gain first. The spike shows very high input drive relative to the expected
output, so the amp gets fault 17.
I don't know why the poster's amp is reporting fault 1, which is a PIN diode
fault. Not sure if a spike can cause this.
73, Dick WC1M
Hi Dick & all...
Dick, I believe your timing explanation as to why you see Fault 17 (low
gain)rather than Fault 13 (overdrive) is precisely correct. I remember
discussing the exact same issue with the guy(s) who knew the 87A code best
- probably 7 or 8 years ago.
Your discussion of transceiver spikes is right on, as well. I've encountered
large initial rf output spikes on the IC-781, TS-940, -950SD & -950SDX, and
FT-1000D. ETO/ALPHA lab techs used to reset a TS-940's internal ALC to get
more output for various tests, and discovered that they could put out brief
initial spikes up to 400W!
With the TS-950SD & FT-1000D, the cause is usually, in my experience, a
cockpit problem resulting from (a) not reading and following the transceiver
manual OR (b) the manual's giving inadequate or no instructions as to how to
set the xcvr DRIVE control (the Yaesu label; I think the equivalent front
panel knob on the TS-950s is called something different, but don't have one
here to look at). In any case, it determines the amount of xcvr INTERNAL ALC
feedback required to deliver desired Pout from the transceiver.
The xcvrs have ALC meter functions and it's easy to set DRIVE during actual
operation with the xcvr delivering the desired Pout. Just switch the meter
to ALC and, either key-down or while talking normally on SSB, adjust DRIVE
so ALC peaks are around the middle of the normal range marked on the meter
scale. This is probably in the area of 6 dB. If the transceiver drive
control is set too high relative to actual operating Pout, a big initial
spike does in fact get through to the output. This is because of the finite
time (on the order of a millisecond or two, typically) that it takes the
xcvr ALC to respond and bring Po down to the preset level.
We've found that many guys tend to crank up the exciter drive control by the
seat of their pants and then set its Po with the RF OUTPUT control - never,
or at least never again, checking the ALC. In a common situation, e.g.
running ~50W to drive an 87A to maximum legal output, using an xcvr capable
of 150-200W, most modern SS xcvrs will put out substantial spikes if their
peak ALC exceeds 6 dB or so.
The GOOD NEWS is that when transceiver ALC is set reasonably close to normal
by proper adjustment, the problem goes away. I used a TS-950SD for
~2 years with my 87A, then an FT-1000D for the past 6 years or so. Unless
the operating conditions (mainly exciter output power) are changed fairly
drastically, it's generally sufficient to check exciter ALC only when there
seems to be a problem. I do it maybe once a month just to be safe.
NOTE that every reference to ALC above refers to ALC within the transceiver
itself. Personally I never use external ALC feedback from the ALPHA to the
xcvr, and we do not recommend it in general. It's completely unnecessary.
Hope this is of interest, and maybe even helpful, to somebody. Sorry to be
so wordy - don't know how to explain this particular issue briefly!
73, Dick W0ID (formerly W4ETO)
> -----Original Message-----
> From: Floyd Sense [mailto:fsense@charter.net]
> Sent: Tuesday, October 11, 2005 10:50 AM
> To: Gudguyham@aol.com; amps@contesting.com
> Subject: Re: [Amps] alpha 87a and Pro II question
>
> 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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