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

"Kerry Miller" wrote in message
news:CNEzf.140599$WH.64582@dukeread01...
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

Kerry -

From you description, you have lost REGULATION .

Read the KBT web site for ALL required diagnosis and repair steps for linear
power supplies and Astron. MENU BAR is GRAY LIST ON LEFT
http://www.kbt-dc-supplies.com/index.php

Replace LM723 regulator chip ...
TEST PASS TRANSISTORS (2N3055 or 2N3771)

How it Works - David Metz's classic article - now 10 years old
http://www.seits.org/features/pwrsup.htm

Index & schematics for Astron power supplies
http://www.repeater-builder.com/astr...ron-index.html

gb

Astron linear supplies use a 3 terminal regulator, usually an LM317. These
things do tend to fail from time to time. Can't tell if that's your
problem, but it is likely, and the things are cheap enough it's worth
popping a new one in to find out.

...


"Kerry Miller" wrote in message
news:CNEzf.140599$WH.64582@dukeread01...
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

"xpyttl" wrote in message
news
Astron linear supplies use a 3 terminal regulator, usually an LM317.
These things do tend to fail from time to time. Can't tell if that's your
problem, but it is likely, and the things are cheap enough it's worth
popping a new one in to find out.


Really? What model of Astron linear power supply have you repaired or seen
that uses this design approach? I have never seen one like this -- over
past 20 years.
Confusing this with some other mfg. design?

Astron has been using the 14-pin (30 years old) LM 723 regulator IC with NPN
pass transistors (e.g. 2N3055, 2N3771) ... for as long as I have been
repairing them.

Check here for correct Astron information - repairs, etc.
http://www.kbt-dc-supplies.com/index.php

and Astron schematics (which show the LM723, not the later LM317 design)
http://www.repeater-builder.com/astr...ron-index.html

gb

gb wrote:
"xpyttl" wrote in message
news
Astron linear supplies use a 3 terminal regulator, usually an LM317.
These things do tend to fail from time to time. Can't tell if that's your
problem, but it is likely, and the things are cheap enough it's worth
popping a new one in to find out.



Really? What model of Astron linear power supply have you repaired or seen
that uses this design approach? I have never seen one like this -- over
past 20 years.
Confusing this with some other mfg. design?

Astron has been using the 14-pin (30 years old) LM 723 regulator IC with NPN
pass transistors (e.g. 2N3055, 2N3771) ... for as long as I have been
repairing them.

Check here for correct Astron information - repairs, etc.
http://www.kbt-dc-supplies.com/index.php

and Astron schematics (which show the LM723, not the later LM317 design)
http://www.repeater-builder.com/astr...ron-index.html

gb


I can confirm that mine has a 723, not a 317. Thanks for the web sites,
looks like some great information. I hooked up that headlight tonight
but it ran fine, pulling a bit over 3 amps for an hour or so. Maybe I
need more load to make it lose regulation.

Guess I'll start digging into that regulator board, the transistors and
all the big things like the transformer seem to be fine.

Thanks,
Kerry - WD5ABC

"Kerry Miller" wrote in message
news:UP_zf.140961$WH.46302@dukeread01...

I can confirm that mine has a 723, not a 317. Thanks for the web sites,
looks like some great information. I hooked up that headlight tonight but
it ran fine, pulling a bit over 3 amps for an hour or so. Maybe I need
more load to make it lose regulation.

Guess I'll start digging into that regulator board, the transistors and
all the big things like the transformer seem to be fine.

Thanks,
Kerry - WD5ABC

First, test each NPN transistor with a VOM or DVM ... both methods of proper
measurement are outlined (added proper method for DVM testing to procedures)

Second, discharge electrolytic capacitors before removing or inserting the
LM 723
Most Astron regulator boards have a socket for the LM 723, IF not after
removing, install socket - observing proper placement of pin 1.

Check bridge rectifier and diodes in circuit.

The KBT site suggests substitution of a resistor value. There are also
suggestions for bypass capacitors.

Stray RF in your radio shack can cause problems in some supplies.

gb

On Thu, 19 Jan 2006 23:47:24 -0600, Kerry Miller
wrote:

gb wrote:
"xpyttl" wrote in message
news
Astron linear supplies use a 3 terminal regulator, usually an LM317.
These things do tend to fail from time to time. Can't tell if that's your
problem, but it is likely, and the things are cheap enough it's worth
popping a new one in to find out.



Really? What model of Astron linear power supply have you repaired or seen
that uses this design approach? I have never seen one like this -- over
past 20 years.
Confusing this with some other mfg. design?

Astron has been using the 14-pin (30 years old) LM 723 regulator IC with NPN
pass transistors (e.g. 2N3055, 2N3771) ... for as long as I have been
repairing them.

Check here for correct Astron information - repairs, etc.
http://www.kbt-dc-supplies.com/index.php

and Astron schematics (which show the LM723, not the later LM317 design)
http://www.repeater-builder.com/astr...ron-index.html

gb


I can confirm that mine has a 723, not a 317. Thanks for the web sites,
looks like some great information. I hooked up that headlight tonight
but it ran fine, pulling a bit over 3 amps for an hour or so. Maybe I
need more load to make it lose regulation.

Guess I'll start digging into that regulator board, the transistors and
all the big things like the transformer seem to be fine.

Thanks,
Kerry - WD5ABC

I would look at the radio first. Put an ameter in the 12 volt line to
the radio and see how much current it is actually drawing.

73
Gary K4FMX

Gary Schafer wrote:

I would look at the radio first. Put an ameter in the 12 volt line to
the radio and see how much current it is actually drawing.

73
Gary K4FMX

Actually, I first thought it was an antenna problem, the rig acted just
like I had a bad problem with RF in the shack. I spent all of one
afternoon reworking the grounds and tuning the antenna. I've got the
best-tuned 4BTV in Texas! I tried it on a dummy load and had the same
problem. So, I pulled it off the power supply and ran the rig (Yaesu
FT-990) from the battery in my truck and it works fine. I also tried
the supply on a second rig, a TS-430, with exactly the same problem -
when I transmit the lights on the rig dim and it drops out of lock. The
430 is my mobile rig, it works fine in the truck but not on the PS.

I'll follow you guys' suggestions to start testing parts. I'm in a
fairly small town, so while I bought a 1000uf capacitor today at Radio
Shack, they can't even order an LM723 so I'll have to find someplace
else to get one.

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.

I have built regulated supplies but it's been 20 yrs since I tinkered
with anything analog, so I'll take all the help I can get! The info at
those links looks helpful, along with the ideas you guys have given me here.

73,
Kerry
WD5ABC

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
Sounds like to me the "Fold-back Regulator circuit" just cut-in, during
operation, if a adjusted threshold value is exceeded, instead of popping
a fuse, the circuit just drops to a low value until the circuit is
re-set by powering-Down and re-started !

Yukio YANO

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