[Icom] PW1 Antenna tuner repairs
Adam Farson
[email protected]
Fri, 31 Jan 2003 20:32:53 -0800
Hi Bob,
Your description of the failure prompted me to compare the output signal
path between the autotuner and the antenna selector relays in the PW1 and
the Quadra. I shall e-mail you the relevant block-diagram sections
separately.
In the Quadra, a reflectometer (L7006 CM COUPLER) between the tuner output
and the common RF rail of the antenna switching relays reports to the CPU
the reflected power at that point in the signal path. This signal serves two
purposes; it allows the load-analyser display to indicate the SWR at the
tuner output, and also causes the CPU to take the amplifier off-line if SWR
> 3:1 at the tuner output. As I mentioned, I had two 20m trap failures in
wet weather - one in a Hy-Gain DX-77 vertical and the other in a Cushcraft
R8. In both cases, the trap arced over. The resulting SWR spike took the
Quadra off-line within a few milliseconds.
The omission of this safety feature from the IC-PW1 is rather regrettable. I
am a little surprised, though, that the sudden change in load impedance
resulting from your antenna failure did not cause the reflectometer at the
tuner input in your PW1 to report SWR out of limits.
Does the PW1 tuner dynamically track load-impedance changes? (The Quadra
tuner does not.) If the answer to the question is "yes", the tuner may have
attempted to follow the wild variations in load impedance caused by your
antenna problem, and at some point the voltage across the variable
capacitors was sufficiently high to break down the air-gap. Repeating the
operation by pressing the TUNE button several times could easily have
generated arcs of sufficient intensity to damage the capacitor plates.
Cheers for now, 73,
Adam VA7OJ/AB4OJ
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Bob Marzari
Sent: January 31, 2003 18:41
To: [email protected]
Subject: RE: [Icom] PW1 Antenna tuner repairs
Hi Adam,
I marked the insulated couplers on the caps indicating full mesh. Am
downloading the manual now. Will have the factory one in a week along with
the caps.
I do not know why the protection circuit did not take the tuner off line.
Probably operator error... :( Repeated pressing of the tune button....
Thanks,
Bob, W3PT
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Adam Farson
Sent: Friday, January 31, 2003 8:59 PM
To: [email protected]
Subject: RE: [Icom] PW1 Antenna tuner repairs
Hi Bob,
Firstly, you can download the PW-1 service manual here:
http://www.qsl.net/icom/manuals.html
Scroll down to "Download IC-PW1 Documents"
When you replace the capacitors, I believe that you may need to recalibrate
the autotuner. This involves positioning the capacitor rotors at the correct
default angle on the servo-motor shafts. (This procedure is required in the
Yaesu Quadra amplifier, but may not be for the PW1).
This procedure is not mentioned in the IC-PW1 service manual. It may be a
good idea to contact the PW1 expert at Icom Service (1-800-USA-ICOM).
Hate to mention this here, but it comes as a profound shock to me that
unlike the Quadra, the PW1 does not have a reflectometer at the autotuner
output. I have had traps blow up whilst transmitting at 1kW PEP on 20m; the
reflectometer in the Quadra caught the resulting impedance anomaly and took
the amplifier off-line instantly.
Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Icom FAQ Site:
http://www.qsl.net/icom/
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Bob Marzari
Sent: January 31, 2003 14:29
To: Icom
Subject: [Icom] PW1 Antenna tuner repairs
Hi,
I smoked the two variable caps in the tuner. The amp is located in basement
below me and I was hot and heavy into the 160M CW contest last weekend a had
an antenna problem. The problem caused the caps to arc over and ruined them.
I took the top cover off and with needle nose pliers managed to remove the 2
badly warped plates on one cap and one on the other. This allowed me to see
if any of the other support circuitry was damaged. It wasn't and it tunes
fine but of course that was into a 50 ohm load. It will sorely miss that
capacitance I removed when in the real world.
I do not have a manual, I ordered one today and two caps from Icom. Has
anyone replaced them on this reflector and has some tips?
Thanks,
Love my PW-1
Bob, W3PT
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Your Moderator: Dick Flanagan W6OLD, [email protected]
Icom Users Net: Sundays, 1700Z, 14.315 MHz
Icom FAQ: http://www.qsl.net/icom/
----
Your Moderator: Dick Flanagan W6OLD, [email protected]
Icom Users Net: Sundays, 1700Z, 14.315 MHz
Icom FAQ: http://www.qsl.net/icom/
----
Your Moderator: Dick Flanagan W6OLD, [email protected]
Icom Users Net: Sundays, 1700Z, 14.315 MHz
Icom FAQ: http://www.qsl.net/icom/