Bob
Astron 35A supplies and probably other sizes are
sensitive to the SCR triggering. One of the
causes I found was due to a shift in the initial
routing from the rectifier to the
capacitors. When you put a supply back together
be sure to give as much space as possible between
the gate lead of the SCR and those wires going to
the rectifier. Capacitor inrush at the peak of
the 60Hz power turn on is prone to trigger the SCR.
Gran K6RIF
At 07:53 AM 12/8/2008, you wrote:
I've had DMMs also go nuts at my site too.
Luckily the Astron supply hasn't had that problem yet.
The fuse usually blows when something
catastrophic happens. One such thing is when the
output voltage goes too high and the built-in
SCR crowbar fires. It shorts the supply
immediately, and the excess current usually
causes the fuse to blow. Sometimes it also
causes the diodes to short out, and they end up
blowing the fuse. RF getting back into the
supply can trip the SCR. Even RF riding on the
supply lines can cause the voltage that the SCR
sees to be high enough to trip it, even though
it may not show up with a meter or even a scope.
You've probably done all you can with the
ferrites unless you missed the wires going to
the SCR. On some supplies it's mounted to the
chassis and has fairly long wires (just waiting to pick up RF) running to it.
You'd be better off with ANY kind of unregulated
power supply, such as what you had with the
MICOR supply. Ferro-resonant transformers
usually aren't susceptible to such RF problems,
and there's nothing electronic such as a crowbar
inside to trip and blow the fuse. This doesn't
explain why your MICOR supply blew its fuse,
unless you exceeded the output current
capability. Most MICORs were only rated up to
100 watts, and the supplies probably are good to
25-30 amps MAX; it seems that your PA is already
exceeding that. Then you tack on a receiver,
exciter, etc, and you've gone past the limit for
the MICOR supply. Even an MSF5000 supply would
be strained to handle that much current; that's
why the bigger stations have TWO supplies, one
for each PA, and the VHF stations have 28V supplies in them.
Solutions? You might consider a battery and a
charger that's strong enough to keep the PA
happy, to run just the PA. Split everything else
off and run that on another smaller supply.
Consider a switching regulator supply, rather
than a linear regulator supply, to run the rest of the equipment.
I know that some of the high power amps are now
being built to run on 24-28VDC. This cuts the
current consumption in half and they can be run with switching supplies.
Let's hope Skip comes aboard here. I know he's
had experience with these units.
Bob M.
======
--- On Mon, 12/8/08, n9wys
<<mailto:n9wys%40ameritech.net>n9...@ameritech.net> wrote:
From: n9wys <<mailto:n9wys%40ameritech.net>n9...@ameritech.net>
Subject: [Repeater-Builder] Astron P/S question
To:
<mailto:Repeater-Builder%40yahoogroups.com>Repeater-Builder@yahoogroups.com
Date: Monday, December 8, 2008, 10:20 AM
For the learned group here
Â
I know there has been some discussion on one the
list regarding Astron Power
supplies. Unfortunately, searching hasnât
revealed what I am looking for, so I pose my
query here and apologize in advance if this was
a subject that was discussed at length in the
past
 I will ddescribe my problem in detail,
so forgive me for being so verbose right off the
bat; but I figure if I provide a lot of info
now, it will avoid a lot of question and answer
exchanges later in order to get an understanding of my problem.
Â
I have a UHF ham repeater system (TKR-820 as
transmitter, MICOR SpectraTAC receiver and
comparator, Astron RM-70 Power Supply, and
Crescend 150W P/A) that is experiencing issues
with the power supply. Seems that when the
repeater is on the air for any time (for
example, over three minutes key-down) the power
supply blows a fuse. The first time this
happened, I changed out the P/S with a MICOR
supply I had from a 100W continuous duty
station. It also blew THAT fuse
 The Astron
supply that blew the fuse had two bad diodes in
the rectifier, so that was repaired. There was
nothing found wrong with the Motorola supply,
other than the main fuse had blown.
Â
I took the PA back to Crescend, but they found
nothing wrong with the P/A. Â The station was
put back on the air with the repaired Astron
supply. Was on the air for about two weeks,
and failed again while I was talking to another
ham. Went back to the tower and found the fuse
blown again in the supply. I took the PA
offline and brought it back to Crescend, told
them of the issue with the P/S, and that I
needed them to check the PA for problems. Their
service tech called me and said heâd had the
PA running on his workbench as we spoke, and had
it transmitting for about 45 minutes with no
problems all operating within spec (~32AA
nominal - 38A max draw @ 165W output). After
we talked some more, he said heâd leave it run
all night. If it was OK, heâd ship it back.
I got the PA back the following Tuesday. I put the station back on the air
Â
In the meantime, I spoke with an engineer from
Crescend who told me that they had some
experience with RF getting into Astron supplies
so wheen I took the PA back to the tower, I put
ferrites on the A+ and ground leads to the P/S
from the PA. (There are about 10 wires
altogether in the power cable going to the PA
two bundles of three A+, and four Grrounds.)Â I
put three ferrites altogether on the DC lines,
and made three turns through the ferrites with
each bundle. Â These were installed as close as
physically possible to the power supply. I also
put one turn on a ferrite for the entire bundle
at the PA end. (Couldnât do more than that
was running out of cable length for hook-up.)
Â
I replaced the fuse again, and got the station
back on the air. Worked for about 45 minutes
(or long enough for me to be far enough away
from the tower where I couldnât make a return
trip that day) and promptly blew the fuse again.
(Or so I suspect.) Â I havenât had a chance to
go back to examine the cause of the failure this time yet. Â
Now hereâs the WEIRD part
 when I was at
th the tower with another tech and replaced the
fuse the time before the last failure, we tried
to use his DMM to check the P/S fuse for
continuity. His meter acted as if the battery
was dead but later investigatioon revealed
that the meter was getting hit with RF from
another transmitter at the site. So Iâm
thinking that the RF problem may or may not be
directly related to MY transmitter. (There is
VHF 100W MICOR transmitter directly next to my
equipment rack that is on 161.325, and transmits 24/7/365.)
Â
OK here are the questions:Â 1) Has anyone
experienced an isssue with RF getting into
Astron power supplies, and how did you remedy
the issue? 2) Since the P/S fails only when my
transmitter is on the air, could I be getting a
mix of RF (the VHF and my UHF) that is causing
this? To answer a question that may be posed,
I do not have a SpecAn available to me to check
for spurs, but I am contacting the county radio
tech (itâs a county-owned tower) to see if he can assist me with this.
Â
Any ideas, other than purchasing a
âhardenedâ power supply, that could remedy my situation?
Â
Thanks,
Mark N9WYS
