Batboard

Hello everyone...

I've got an Astron RM35 Power supply thats been running flawlessly for a couple years now. The other day I observed the meter was reading ~5V. This seemed wrong. I felt the back... warm, but not unusual. Checked connections to mgake sure there wasn't any shorts, etc. Everything checked out ok. I pulled it out from the wall and opened it up. I checked the voltage right out of the transformer and it read 21V. Good and strong. I removed the leads that went to my TS2000 and IC706MKIIG and the voltage came up to 11V. I dont know much about power supplies but I did have a spare set of finals. I changed them and it didn't fix it. The only thing I can come up with is that there is an orange wire that connects to a lead on each of the 4 finals, and back to the circuit board the output of the transformers connect to and the huge filter capacitor. Does this orange wire control the output of the finals... regulation? Is there something I can do to fix this thing? It's a great power supply and I'd hate to see it end up being junk. There's got to be something I can do to fix this guy. It seems like its got to be a simple.

Anyone have any ideas? Thanks guys.. I'm off the air until I can get it fixed or replaced.

Scott.

If you unhooked the radios and the voltage came back up you have one of two things.

A shorted radio.

A faulty supply current issue.

The power supply has a current limiter correct? Most do. Either it is set too low or faulty. The voltage drops when the current is maxed out on the supply and cant / wont supply more.

Or you have a short in one of the radios causing the same issue. Max current avaliable reached = voltage drop.

Hook an Ammeter capable of displaying a high value (and not exploding) inline with the supply. Then hook up the radios and see if one is drawing too much current.

Or you could get a 1ohm resistor capable of handling some high current and put it inline and measure the voltage across it which will give you current.

The voltage only comes up to 11V. usually it's almost 14 and snaps right up there instantly. Currently without anything connected, it slowly swings up to ~11V. Therefore I dont think it's a short in a radio. One of the radio is on so it's probably trying to power up causing the voltage drop. Based on your offered suggestions, I'm guessing its limiter issue but dont know where to start. There is a single IC in there and a bunch of resistors and diodes. I could test everything except the IC. Maybe I should check components and then replace the IC?

Replace the IC. For some reason, the RM35s have had that problem. I have replaced mine about 3 times over the past 5 years.

I keep one or two spare ICs on hand at all times.

I'm using the 723 chip; Rat Shack #276-1740. I cleaned out my nearest Rat Shack when the last chip went in my supply.

Just my experience.......



Jack

Excellent!! I'll give it a try tomorrow as soon as I get home from work. Thanks... I'll report my findings tomorrow evening. Anyone have any tips just in case?

Scott.

Just unplug it from the wall before you start farklin' with it (experience talking)..........

Should be OK after you change the chip. You'll have to reset your voltage and any limiting you put on it, but other than that you should be good to go.

I don't know why Astron has this problem, but apparently it is quite common.


Jack

wanna que me in on how to set those things? I've never played with the internals of a "real" power supply before.

I may be mistaking your model number - the one I have has a voltage meter on the right, and an amp meter on the left - has a voltage adjust knob on the right and an amp limiter knob on the left.

You probably should check your IC number in case they use a different one in your supply, but it is probably still the problem.


Jack

mine has no adjustment @ the user end. It's ~14V and upto 35 amps. not adjustment. Just the two meters.

Astrons are famous for the pass transistors, the ones on the back heatsink, comming loose and usally opening up. Some times they short due to the one that still has connections has to handel ALL the current. The screws securing the pass transistors come loose due to heat and cooling. Pull the transistors, check them with an ohm meter and clean the old "grease" from the mica insulator and put new fresh grease, clear silicon grease works just fine. Add a shakeproof internal tooth lock washer on each screw, two per transistor, the Collector terminal.

The schematic is the same for several models, just the transformer, and the ammount of pass transistors are different.

I would swap out the 723 regulater IC--they are subject to failure, though when they do, the output will USUALLY run wide-open(high). I would get a spare even if tightening up the conn. fixes it--they are not expensive. Blitz.

I pulled a 723 from another broken astron I had lying around. Identical problem with the other IC. Odd though, when I turned it on.. it didn't do much then I heard the transformer make a bang as it snaped to life and pushed the needle to ~11vdc. Still not right. I put a piece of equipment on it and it immediatly dropped to 5v. Useless. I'll pick up a couple brand new IC's from Radio Shack this afternoon @ lunch to try tonight. I noticed a large transistor in the bottom of the power supply which had the ground and the output going into it (14ga wire) with a purple wire (22 ga) connecting to the last lead. It seems to me, if this transistor was bad, it could be shorting out my supply for me. Anyone know what this thing is for? It looks like a possible point of failure.

I can't help with particulars on your power supply, but I'd suggest contacting Astron tech support. I've found them very responsive and helpful over the years.

My two cent's worth. I have fixed a couple of Astrons and own two RS-35Ms myself. If the voltage isn't coming all the way up, it could be a driver transistor - the components between the 723 and the finals. The 723 can't provide enough drive current for those big 3055 guys, and any load on the output will drag everything down. Since the finals were already replaced with no effect, then it's time to start working backwards towards the 723, and that's maybe one or two transistors.

There is over-current and over-voltage protection circuitry built into the supply. Too much voltage will trigger an SCR that will short-circuit the output to less than 1 volt. You need to power the unit off for a good 30 seconds to reset the circuit. But this is not your problem if you're getting less than 16 volts out of the supply. The 723 also has the ability to shut down with excessive voltage or current, but I believe Astron is only using the current limiting feature of the chip.

My experience with 723-based power supplies is that the 723 is rarely the problem, even though it's the first thing people replace. There are only a few other transistors in the Astron supplies. Pull them and check them with a meter. Schematics are available on the web, and there's only a slight difference between the ones that are front-panel adjustable and those that aren't. Each will still have a way to adjust the voltage and current, however. There are also adjustment pots on the meters, if your unit is so equipped.

Adjustment is fairly simple. Figure out which pot (on the regulator board) adjusts the voltage, set it to 13.6 or whatever you want it to be. Connect a load to the unit and run it up to about 35 amps if possible, then adjust the other pot until the voltage starts dropping or goes to zero. That should set the current limiter properly. Calibrate the meters with the pots on the back of each one, using appropriate external meters as a reference.

One thing I have found to be unsatisfactory on these supplies is the fact that the wires going to the output studs are only crimped into the lugs. I have removed the lugs from the studs and soldered them, completely filling up the crimp area, to make a much better connection. I had been able to actually wiggle the component leads in those lugs, but not after they're filled with solder.

Bob M.

I went to Radio shack today to get a 723 to replace.. just in case. They dont have them. Screw Radio Shack. I'll never go back there again. They've completly ruined the component section of that store and turned it into a Wal-Mart Electronics Department Annex. I'll check the transistors tonight and order my replacement parts from Digi-Key. maybe I'll just scavange the whole regulator board from my other supply for now. i'll report tonights findings when I finish diagnosing.

Scott.

Yes, it's horrible. They've gotten rid of so much lately.

I've had good luck with small orders from Mouser, but your mileage may vary, and some people swear by Digikey (others swear at them).

I just went looking for a schematic - they seem to have been removed from the repeaterbuilder site. If you need one, I can take a picture of mine and e-mail the resulting JPG file. Provide an e-mail address in a PM if you want one. It'll certainly help.

Bob M.

I agree, working back from the "finals" transistors, checking the TO220 driver transistor next. The circuit is not anything trick, fairly straight forward. The "road map" will definatly help.

First, they're not called finals in a power supply, they're called pass transistors.

One thing you might check is the voltage on the large filter cap, it should be somewhere around 25 volts I believe, see if it drops much when you put a load on the supply, if it does you've probably got a bad bridge rectifier, or possibly transformer. The rectifiers go bad a lot in Astrons, but they usually short, blowing the fuse. If one diode in it is open you might get the symptoms you said.

For parts, I would go with Mouser for small orders, Digikey has a minimum, I think it's $20, below that you pay an extra $5. I've used both suppliers for years, both are good.

As for Radio Shack.. gack.. unless you want to buy a cellphone there's no reason to ever go there again.. they've pretty much eliminated any kind of electronic parts.. shame...
I went there a while back looking for an MOV.. the girl at the counter says 'I don't know what that means.. that's Greek to me..' almost as bad as when they tried to sell me a $30 service plan on a $20 pair of headphones.. the guy says 'but what if they break?' umm... I'll buy some new ones? Pathetic..

I, too have had to replace a few of the reference IC's in those supplies, as have a few other people I know.

Also, Blitz said that the IC going would usually make the output go high instead of low. That is true sometimes, but they also sometimes go low; I have seen it myself. If you can get a schematic for the unit, it should have a chart giving the proper voltages at various pins of the IC. If any of them, mainly on the "output" pins, are very far off, that is most likely the problem.

As for the device you described in the bottom of your supply sounds like an SCR to me. It is, basicly, a "switchable diode", and is in the supplys "crowbar" circuit. It is used to create a "dead short" in the output, thus blowing the output fuse, in an excessive current situation. Could be a problem, but they are usually either "open" (normal), or "closed" (excess current).

Well, since they're ALL pass transistors, how would you refer to the last ones that actually control the voltage and current to the load? The word "final" certainly seems to describe their function rather well. It doesn't only have to refer to amplifiers, tubes, examinations, or obituaries.

Don't have a cow about some term that you may not personally use in daily language. Not everything in life is 101% perfect like you.

Bob M.

Thus spracht Bob M.:
Well, since they're ALL pass transistors, how would you refer to the last ones that actually control the voltage and current to the load?

Well, since they're NOT all pass transistors, you would refer to the last ones that actually control the voltage and current to the load as, get ready for it...... pass transistors. Strike one.

und dann sagte er:
The word "final" certainly seems to describe their function rather well. It doesn't only have to refer to amplifiers, tubes, examinations, or obituaries.

That's all very nice, but it's not correct. Strike two.

Und finally(pun intended):
Don't have a cow about some term that you may not personally use in daily language. Not everything in life is 101% perfect like you.

But I do use the term in my daily language, I just don't use it to incorrectly describe pass transistors. I also didn't have a cow, I simply stated the correct term, since several people didn't appear to know it. It's called being helpful. Having a cow would be what you did.. there, you've now learned two terms today. And he goes down swinging.....

In their specs for the 723, both National Semiconductor and Signetics refer to the output transistor in the IC as a series pass transistor with a maximum output current of 150 mA, and higher currents can be obtained with additional external (pass) transistors.

You can call any of the transistors in the chain pass transistors because that is their function. They just operate at increasing higher current levels. Calling the last one the final makes perfect sense since it is the final position in the stack with the function of a pass transistor.

Either name should be clear to most people working on power supplies. One name refers to its function and the other to its position. You may even call them output transistors if they are the final ones.

Likewise, in a RF amp, you call all transistors RF amplifying transistors but call the last one the final (RF amplifier transistor).

Nand.

-that many just don't relate to...Yes they ARE "pass", just used to working with systems that refer to the load-bearing devices as "finals"(audio and rf amps). Some have to show off their knowledge by incessant nit-picking the statments of others--used to work with someone that did so, constantly--glad I no longer do. Thank you to those who DO understand. Blitz.

-that many just don't relate to...Yes they ARE "pass", just used to working with systems that refer to the load-bearing devices as "finals"(audio and rf amps). Some have to show off their knowledge by incessant nit-picking the statments of others--used to work with someone that did so, constantly--glad I no longer do. Thank you to those who DO understand. Blitz.

-that many just don't relate to...Yes they ARE "pass", just used to working with systems that refer to the load-bearing devices as "finals"(audio and rf amps). Some have to show off their knowledge by incessant nit-picking the statments of others--used to work with someone that did so, constantly--glad I no longer do. Thank you to those who DO understand. Blitz.

-that many just don't relate to...Yes they ARE "pass", just used to working with systems that refer to the load-bearing devices as "finals"(audio and rf amps). Some have to show off their knowledge by incessant nit-picking the statments of others--used to work with someone that did so, constantly--glad I no longer do. Thank you to those who DO understand. Blitz.

-"knowledge show-off". I used to work with an individual with a poor self image--He would constantly "correct" and condemn others to build himself up. Glad NOT to see him anymore--was a REAL pain to be around. **PLEASE** Batlabs is NOT the place for petty & insecure--DROP IT and move on--most THINKERS knew what he was saying. Blitz.

1) all astrons suck

2) they are called pass transistors, calling them anything else shows you're "wet behind the ears"

Could you post that a few more times?
Anyway, as I stated before, I was not trying to put anyone down, as you all are, I was merely pointing out the correct term, for trying to be helpful I get this crap from a bunch of ingrates.

You all freak out at the possibility that you were wrong about something and I'm insecure?

Ok, that's two up, two down.. next batter...

note to Jack and Blitz...read JAYMZ' signature....

Hey guys.. Thanks for all the suggestions to get this thing working again for me. I went to HossTraders ham fest in New Hampshire last weekend and picked up a VS-50M for $125.00 mint. sold the broken RS-35M for $40.00. outof my hair and written off as a loss. Oh well.

Thanks again everyone.. I think the repair would have taken me more time than it was worth anyway. My expertise are good enough to have fixed it quickly enought to have made it worthwhile. I discoverd that after working on it for almost a week.