Hi Don,
Another thought... have you noticed whether the Fault 17 occurs when
changing bands? If so, here is another note I found in my files from Glenn
at Alpha years ago where a misalignment of the frequency detect can lead to
Fault 17:
73 es HH
Jerry NY2KW
******************************************************
Alpha 87A Frequency Detect Adjustment:
The pot in the bottom of the 87A is to be adjusted as follows.
1. Place the 87A on it's right side.
2. Remove the bottom cover under the tubes.
3. Place the transceiver on 28mhz and adjust the power output to 5 watts.
4. Place the amplifier in the 160 meters position.
5. Put the pot in the full clockwise position to start.
6. Key the radio and adjust the pot counter clockwise until the amplifier
changes bands then stop there.
7. Replace the covers and place the amp back flat on the table.
*******************************************************
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Don Moman VE6JY
Sent: Thursday, December 08, 2016 9:46 PM
To: Amps@Contesting. Com
Subject: [Amps] Alpha 87a issues - fault 17
Just in case someone has come across this particular issue and maybe save me
from reinventing the fix for the wheel....
87a with AlphaMax, has been running fine for years with Icom 7800 as the
driver. Rarely used though, maybe once every few weeks. Other amps have
no issues. Have been noticing it has been faulting out more and more
easily, with fault 17 code (arcs or abnormal gain). Seems OK - or at least
better - at the start but seems to fault progressively easier. The amp is
being driven very conservatively, monitor scope in line, issue not band
selective. Plate current on peaks is around 1 amp.. It is not an overshoot
issue. Took it out of its' rack position today and did some more testing.
First thing I noticed - when I plug in the 220 line the fan didn't jump. It
always has, just for an instant. Warmup and everything is fine. Then with
Alpha Max enabled, the output gradually retuned itself from maybe 1 kw to
only a few hundred watts. Internal bargraph agrees with external power
meter. Going to the default stored position, it was back to ~1 kw. (not
max, just for the drive I used). I started doing some manual tuning, since
the AlphaMax software wasn't - it had always worked fine before. Then I
noticed the led when in the Tune position on the bar graph always stayed in
the center. In the past, it had moved with the tuning, as it should. All
the other functions of the bar graph appear to work fine. The tune motors
all function OK and I could peak the output, but it was now starting to
fault out with Code 17. Had cover off at this stage, no arcs, nothing
visibly wrong. It faults at only a few hundred watts when warm now.
I'm not convinced it is a "real" fault 17 issue. I could swap out the tubes
but I'm not convinced that would change anything. I want to see if the Auto
Tune LED moves when the unit is cold - waiting for that while I type this.
I think that and the different behaviour in the fan when first plugged in,
are clues. Is there a common power supply voltage - out of spec, drifting or
missing - that could cause this? Or the sensor that drives the Tune bar
graph isn't and its voltage is also used in part of the sensing for plate
current?
Thanks for any insight...
Don
VE6JY
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