astron 35-M wont go

[N8ETQ]

 Yo'

  Got an astron 35-M that wont go to 13.8vdc out when I turn it on
with a 25A load. It will cook that thing all day long but just wont
"Start" with that load.   With that load the V meter reads about 5
and the A meter reads about nuthin'. Remove the load and turn it on
all is gud, add the load, no problem. goes all day. WTF?

/Dan

[Detroit47]

Disable the crow bar, but you will have no short protection. Look at the schematic and you will see it, I don't remember if it is adjustable on that one. As I recall the regulator IC prone to failure.

John

[Mike/W8BAC]

Check to see if your Astron model has a current limiting, fold back circuit built in. If so it's my guess the current limiter sees the load, at start up, as a short. That's asking quite a bit from any supply to go from zero to a 25 amp load on start up.

You might think about a step start or relay delay for the load. Even a second or two might give the power supply time to hit baseline and spare the load any transient spikes.

Mike

[Pete, WA2CWA]

Astron Linear Power Supplies:
SPECIAL FEATURES

    SOLID STATE ELECTRONICALLY REGULATED
    FOLD-BACK CURRENT LIMITING Protects Power
    Supply from excessive current & continuous shorted
    output.
    CROWBAR OVERVOLTAGE PROTECTION on all
    Models except RS-3A, RS-4A, RS-5A, RS-4L, RS-5L
    MAINTAIN REGULATION & LOW RIPPLE at low
    line input Voltage
    HEAVY DUTY HEAT SINK CHASSIS MOUNT FUSE

Full details here: http://www.astroncorp.com/linear.shtml

[w3jn]

Disable the crow bar, but you will have no short protection. Look at the schematic and you will see it, I don't remember if it is adjustable on that one. As I recall the regulator IC prone to failure.

John

The crowbar is for overvoltage protection and although it's a noted problem with these power supplies that's not the problem here, or the ammeter would be pegged and/or the pass transistors fried.

Astron loves to use those stupid LM723 regulator ICs which are a royal PITA.  As John noted they tend to act flaky sometimes.

Finally when you turn those on there's a huge current inrush to charge the 64,000 uF capacitor which tends to fry the on/off switch.  Between charging that cap and the 25A load I'm betting the current limit is getting cornfused as Mike noted.   One of those 10 ohm or so NTC thermistors in series might straighten things out.

Here's a pdf schematic with notations on what's going on in each section of the PS.  It's pretty well designed in most respects, but if I was the designer I would have done something about the current inrush and wouldn't have used a LM723.

http://www.al7fs.us/astron-rs35m%20annotated%203.pdf

[W0BTU]

Check out this eye-opening page about Astron power supplies: http://www.repeater-builder.com/astron/astron-intro-stuff.html. Maybe you'll find something useful there.

[kb3ouk]

that's soething all power supplies seem to have in common, that huge inrush of current when you flip it on. the one i use on my icom (can't remember who made it) is really bad for it, let it set for days then flip it on and it really bangs, you can actually feel the thing jump when it starts receiving power. makes the lights flicker a little. why couldn't they put soe kind of step start circuit in them?

[KC4VWU]

Disconnect the SCR at the output.

73, Phil

[N8ETQ]

Thanks for the input guy's,

   Inrush + load = current limit. Didn't even think about that. Thankyou.
I did order 10 LM723 and thought about trying some other ones but the
switch on this one is already a little "Flakey" so I think I'll pass on that.

Again thanks.

73

/Dan

[Jeff W9GY]

I zapped a 723 in one of those supplies just having too much RF in the shack (running an EF antenna at the time with tuner 10 feet from the supply).  In a nutshell, yes, the 723 is flakey.  Good you bought 10 of them!

[w3jn]

Disconnect the SCR at the output.

73, Phil

I wouldn't, particularly with this supply.  The 723 WILL blow at some time which will put 25V on the output.  The crowbar (SCR) is there for just such an eventuality.  Better to replace some pass transistors and a 723 than ruining a radio.

[N8ETQ]

  Yeah,   Bad medicine, You can completely rebuild these things for
around $6. 4 2n3772's @ 1.20ea  TIP29 @ .35 and the LM723 @ .29.
No need to bet the YaeComWood on that!

Thanks again
73
/Dan

Disconnect the SCR at the output.

73, Phil

I wouldn't, particularly with this supply.  The 723 WILL blow at some time which will put 25V on the output.  The crowbar (SCR) is there for just such an eventuality.  Better to replace some pass transistors and a 723 than ruining a radio.

[W3SLK]

I know of a friend of mine that wiped out his FT-890 with a bad Pyramid supply. I can't remember if it was a switcher or not. I'd rather be safe than sorry. Linear PSU are pretty simple to take care of.

[WD8BIL]

It probablay ain't the inrush current of the power supply as much as the turn on current of the load.
Don't fix anything. Just keep the load off until the supply is up and running.
With now walk in circuit that's the only way you should be operating it with heavy loads.

[KA3ZLR]

Hi,

I never start a DC Supply with a load on it. No No....I never did never will.


73
Jack
KA3ZLR

[AG4ME]

Yes, we see this problem with Astron power supplies in the marine electronics industry.
When an Astron LS-18 (28V 18A)  model is used on a JRC radar (JMA 5300),
the Astron power supply will go into over-current and the output drops
when turning the radar on, most of the time.   Sometimes it will power up.

or while whistling into a marine SSB radio such as a SEA222, while being
powered by a RS-35.

out in the field, I would cut resistor R4.  this disables this
over-current circuit.  I would argue a lot with other technicians
about doing this, so I usually did not tell them. 
I would tell them this circuit is not required.
There are fuses all over the power lines.     

If at the shop, change resistor R4 to 680 ohms or more.
This is what Astron suggests.  Yes, they know about this problem.

or you can put a variable resistor in at R4, and have your load connected
then adjust R4 to shut down.

[K6IC]

It is very easy to install step-start in the AC input of these supplies,  by using a 24 VDC relay coil on the raw DC output of the Bridge,  with the contacts shorting a 100-ish Ohm power R in the AC line input.  IIRC,  Vic

[w3jn]

The NTC thermistor works FB also and it has only 2 legs and is less than a buck.

In an era where power supplies are 10X more complicated than they need to be, these are very simple to repair and generally work very well.  Don't ever turn down a cheap dead hamfest Astron, chances are it's either the switch, the 723, or the pass transistors all of which are really simple to replace.

Wish they woulda used a LM317 instead of the stupid 723 though.  Although it's not the easiest thing to add programmable current limiting to a LM317, it self limits and shuts down if it gets too hot.  Using the LM317 would save a dozen parts and it would be much more reliable.

[KL7OF]

Disconnect the SCR at the output.

73, Phil

I wouldn't, particularly with this supply.  The 723 WILL blow at some time which will put 25V on the output.  The crowbar (SCR) is there for just such an eventuality.  Better to replace some pass transistors and a 723 than ruining a radio.

I have a landfill Astron 50-A that shows 24V dc on the out put....no load...I've never had one of these before...Is this normal?   Is the 723 blown?  (what is the 723?)  Interesting thread..

[N8ETQ]

[/quote]I have a landfill Astron 50-A that shows 24V dc on the out put....no load...I've never had one of these before...Is this normal?   Is the 723 blown?  (what is the 723?)  Interesting thread..
[/quote]


 Probably, plus a pass transistor or 2. The crowbar circuit is open as well.
For diagnosis, temporaraly disconnect the SCR from the output and check
all the pass transistors.  723 = LM723 14 pin dip VR chip.

GL

/Dan

[W1ATR]

Yeah cold starting with load is generally not good for any supply. The astron is no different. C1 is a 2200uF 35V beer can that will suck a lotta current on the initial startup when it's discharged. There's enough headroom in the circuit with a 5, or even a 10A load, but DEF not a 25A load. That's also a fast way to smoke out the rect bridges also. (2x DB3501's rated at 35A each) 

That supply is working exactly as it should be. Always switch the load.

73
J

[w3jn]

I have a landfill Astron 50-A that shows 24V dc on the out put....no load...I've never had one of these before...Is this normal?   Is the 723 blown?  (what is the 723?)  Interesting thread..
[/quote]

Agree.  Also could be the driver transistor and the 723.  Seems like a chain reaction when the 723 goes.

BTW you should NEVER use a power supply that has a 723 in it to charge a battery, or in parallel with another PS, unless you diode isolate it.   Some years ago at work we used an alarm PS with a 723 and a battery backup.  All was fine if you connected the power supply to AC THEN the installed the battery, and it rode thru a power failure fine.  But if you hooked the battery up BEFORE hooking it to AC, instant 723 fry.  I musta replaced 50 723s in these things - and that's where I learned to hate 'em.


 Probably, plus a pass transistor or 2. The crowbar circuit is open as well.
For diagnosis, temporaraly disconnect the SCR from the output and check
all the pass transistors.  723 = LM723 14 pin dip VR chip.

GL

/Dan
[/quote]

[WD8BIL]

I have a landfill Astron 50-A that shows 24V dc on the out put....no load...I've never had one of these before...Is this normal?   Is the 723 blown?  (what is the 723?)  Interesting thread

Check for an open preload resistor. Many regulator circuits need a constant light load to maintain regulation at no load.

[WA1GFZ]

I love the 723 and have been designing supplies using them since the '70S.
The SCR crowbar has nothing to do with the regulator. Bad advice removing the crowbar. If the crowbar fires then add a cap between gate and cathode to kill the hair trigger. It is pretty easy to get one to start into a load if you don't mind the voltage coming up slowly. Just add an RC on the reference output to the error amp so the reference voltage comes up slowly into the error amp. this forces the output voltage voltage to come up slow. Also you can modify the foldback to recover after it has cleared the fault.
Sounds to me the 723 is in a latch mode or the load never charges up to clear the fault. There are many ways to screw up a 723 design but not the fault of the chip.

[The Slab Bacon]

I have an interesting power supply at home. It is a Lapp CR40. It has a rather unusual design. It was made for servicing older tube  / hybrid land commercial 2-way stuff. It is rated at up to 40v (adjustable) and somewhere around 50A. (It's been a long time since I used it.

It has a transformer that looks like it should be in a small welder and has both switching and pass regulation. It has 2 huge SCRs that look like large ceramic sparkplugs that switch rectify the voltage down to about 2v of what you set it for, then only 2 or 3 2N3055 pass transistors that pass regulate it down the last 1.5V to get it to what you want. I guess they do it that way to keep the dissapation down .
It uses a 723 in the control circuit along with a bunch of other stuff.

IIRC it has a bunch of adjustments to "align" it and the proceedure was rather complicated. IIRC, you used to be able to hear the switching rectifiers doing their thing. It made some unusual noises when you loaded it down hard. Especially keying up something like a T74MST or something similar.

Since getting an Astron RS35-M which I now use as the bench 12v supply It rarely / if ever gets used. The RS-35, however has many 1000s of hours on it.