On Wed, 18 Jan 2006 22:43:07 -0600, Kerry Miller
wrote:

I've got a problem with my Astron RS-20 power supply. With no load,
it's fine, but anything above 4amps or so makes it drop way down and my
rig drops out of lock. I haven't measured it under load but the rig
works ok to 10 or 11 volts so it must be dropping below that.

I found a schematic and downloaded it, all the voltages are fairly close
to what it says on the schematic with no load, I haven't made any
measurements with a load on it. I'll pick up a headlight tomorrow to
put a load on it and make more measurements.

Does anybody have any ideas?

Thanks,
Kerry, WD5ABC



Hi Kerry, Since you have the voltage, and I assume that you checked it
at around 13.8 volts, and are not getting the current, there are
usually just a few simple things that usually crap out on these power
supplies. Please note, I have 3 or 4 RS-35s, (not an RS-20) but they
are built alike, enough so, that you should be able to figure out the
problem. First, providing the pass transisitors are good, and with the
power off, and AC unplugged, and filter caps discharged, look on the
backside of the supply, and you will see 4 sets of double paralelled 5
Watt .05 white, square inch long power resistors connected between the
4 pass transistors and BUS. Using a ohmmeter, check these for around
..025 Ohms resistance. If its a taste higher, OK... However, once you
get to around an Ohm or more, your power supply will exibit the
conditions you have mentioned. These resistors provide emitter pass
transistor protection as I recall, and many times will fry, and you
will not know it unless you measure them. If I find these resistors
have gone south, I further test the supply by jumping the resistors
with test jumpers. You'll know right away if the problem went away by
using a test rig to draw some current. PLEASE NOTE, I have fixed quite
a few Astron supplies, BUT if you blow your supply up (or test radio)
even more than it is, don't blame me for any info I have provided. If
it works, change out the resistors. I don't recommend you just jump
them out..Oh, BTW, since you have the LM723 regulator, look on the
bottom side of the board, and see if there is a resistor, hanging in
mid air, which has a wire connected to it that runs down to the bottom
floor of the supply, and is attached to a 3 prong transistor in a
T0-220 case. Sometimes, this resistor will fry, causing current
problems too.. One of my early supplies has the LM317 regulator, but,
you won't have to worry about this, as this requlator is not there,
however, the mounting holes (open of course) are still there on the
mainboard in the upper left corner.. Hopefully, this will help.. Best
Luck OM.. Tony, WB8MLA

In article CNEzf.140599$WH.64582@dukeread01, says...

I've got a problem with my Astron RS-20 power supply. With no load,
it's fine, but anything above 4amps or so makes it drop way down and my
rig drops out of lock. I haven't measured it under load but the rig
works ok to 10 or 11 volts so it must be dropping below that.

I found a schematic and downloaded it, all the voltages are fairly close
to what it says on the schematic with no load, I haven't made any
measurements with a load on it. I'll pick up a headlight tomorrow to
put a load on it and make more measurements.

Does anybody have any ideas?

Thanks,
Kerry, WD5ABC

Is it just simply RF getting back into your supply and causing
havoc? Perhaps the supply is O.K.? You need at least 3 headlights
to get the supply under a load that compares to your rig. Try
more lights and see if it craps out.

In article GNhAf.141967$WH.127022@dukeread01, Kerry Miller
wrote:

Have any of you guys tried the new switching power supplies? I've seen
the one at Radio Shack (claims 25a but I doubt it), MFJ and Astron but
haven't ever used one. I normally just run 1 HF rig (max 100w) and a
small VHF rig (max 25w) for packet. Is a switcher solid and reliable
enough for something like that? I've considered getting something like
that and rebuilding the Astron when I can get the parts.

Kerry-

I have three switching supplies: One from Radio Shack, one from MFJ and
one from Icom (PS-125). They all work quite well as far as delivering
rated current.

The problem is that the high frequency switching noise can be picked up by
an HF receiver. The Radio Shack unit is TERRIBLE in this regard. The MFJ
is fairly good and the Icom is the best. Even so, the Icom switching
noise is picked up if it is anywhere near the antenna.

I'm currently using a makeshift indoor antenna consisting of a dipole made
of a pair of mobile whips on the second floor. Because of the noise
problem, I've gone back to using an old Kenwood linear supply with my Icom
756 Pro II. This radio has the band scope, so you can see the noise floor
increase across the band when the switching power supply is turned on.

73, Fred, K4DII

Fred McKenzie wrote:
In article GNhAf.141967$WH.127022@dukeread01, Kerry Miller
wrote:


Have any of you guys tried the new switching power supplies? I've seen
the one at Radio Shack (claims 25a but I doubt it), MFJ and Astron but
haven't ever used one. I normally just run 1 HF rig (max 100w) and a
small VHF rig (max 25w) for packet. Is a switcher solid and reliable
enough for something like that? I've considered getting something like
that and rebuilding the Astron when I can get the parts.


Kerry-

I have three switching supplies: One from Radio Shack, one from MFJ and
one from Icom (PS-125). They all work quite well as far as delivering
rated current.

The problem is that the high frequency switching noise can be picked up by
an HF receiver. The Radio Shack unit is TERRIBLE in this regard. The MFJ
is fairly good and the Icom is the best. Even so, the Icom switching
noise is picked up if it is anywhere near the antenna.

I'm currently using a makeshift indoor antenna consisting of a dipole made
of a pair of mobile whips on the second floor. Because of the noise
problem, I've gone back to using an old Kenwood linear supply with my Icom
756 Pro II. This radio has the band scope, so you can see the noise floor
increase across the band when the switching power supply is turned on.

73, Fred, K4DII
Thanks for the info. I picked up one of the RS supplies yesterday, and
you're right, it's pretty noisy on 80m, especially on my longwire which
terminates inside the shack. On 40m and above and on the outside
antenna (dipole or vertical) it's fine and below my noise floor. I
found a mod for it with some toroids and caps across the output to
filter it a little, I'll probably try that but it's workable for now
as-is since I don't work much 80m.

It will keep me on the air until I fix the Astron, I'll probably put the
Astron back on the HF rig and use the RS switching supply on VHF and UHF.

73,
Kerry
WD5ABC

Gudmundur wrote:
In article CNEzf.140599$WH.64582@dukeread01, says...

I've got a problem with my Astron RS-20 power supply. With no load,
it's fine, but anything above 4amps or so makes it drop way down and my
rig drops out of lock. I haven't measured it under load but the rig
works ok to 10 or 11 volts so it must be dropping below that.

I found a schematic and downloaded it, all the voltages are fairly close
to what it says on the schematic with no load, I haven't made any
measurements with a load on it. I'll pick up a headlight tomorrow to
put a load on it and make more measurements.

Does anybody have any ideas?

Thanks,
Kerry, WD5ABC


Is it just simply RF getting back into your supply and causing
havoc? Perhaps the supply is O.K.? You need at least 3 headlights
to get the supply under a load that compares to your rig. Try
more lights and see if it craps out.


Nothing normal ever seems to happen to me... I did go out to get a 2nd
headlight so I could get about 7.75 amps on it. I found a 1000uf
capacitor that had a leg corroded so badly that apparently during the
move it wiggled around enough to break loose. I went to the local Radio
Shack (which, by the way, has apparently turned into a cell phone store)
and they didn't have any 1000uf but they did have some 470uf caps so I
put two of them in parallel to get close to see if it mattered. Pins 11
and 12 showed about 8 or 9 volts too low before but now they are right
on according to the chart on the Astron schematic. I connected one
headlight (3.75 amps) and turned on the supply. It showed 13.59 volts.
Then I connected the 2nd headlight (4 amps) and it stayed dead on
13.59 volts. Looks like I'm in business!

Somebody has been into this supply before and butchered it, so I may
clean up a few things while I'm in it. I guess I should fix that
capacitor, the next guy in there will say the same about me if he sees 2
paralleled 470ufs instead of a 1000 uf!

THanks for your help guys!

73,
Kerry
WD5ABC
PS This post may look different, I'm on my Linux box out in the shack
tonight.

....[snip]....
and they didn't have any 1000uf but they did have some 470uf caps so I
put two of them in parallel to get close to see if it mattered....
^^^^^^^^

I sure hope you meant "series"!-)
---
--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

On 25 Jan 2006 21:43:04 -0600, wrote:

....[snip]....
and they didn't have any 1000uf but they did have some 470uf caps so I
put two of them in parallel to get close to see if it mattered....
^^^^^^^^

I sure hope you meant "series"!-)

Why?

Mcalhoun must have been thinking about resistors!

"budgie" wrote in message
...
On 25 Jan 2006 21:43:04 -0600, wrote:

....[snip]....
and they didn't have any 1000uf but they did have some 470uf caps so I
put two of them in parallel to get close to see if it mattered....
^^^^^^^^

I sure hope you meant "series"!-)

Why?

In article , wrote:

....[snip]....
and they didn't have any 1000uf but they did have some 470uf caps so I
put two of them in parallel to get close to see if it mattered....
^^^^^^^^

I sure hope you meant "series"!-)
---

I hope you are an underclassman, who hasn't actually taken any college
level classes in Electronics Design or Circuit Evaluation. If not,
you definitly ask for your money back, because you didn't learn anything.

Me

Me wrote:
In article , wrote:

....[snip]....
and they didn't have any 1000uf but they did have some 470uf caps so I
put two of them in parallel to get close to see if it mattered....
^^^^^^^^

I sure hope you meant "series"!-)
---

I hope you are an underclassman, who hasn't actually taken any college
level classes in Electronics Design or Circuit Evaluation. If not,
you definitly ask for your money back, because you didn't learn anything.

Me
2 470uf in parallel is close to 1000uf. This was on the Extra class
Ham exam. I got my ticket 40 years ago. Why do you think an Amateur
Radio Operator should necessarily have college level Electronics Design
Experience? This is an Amateur newsgroup, unless cross-posting.
Gary N4AST