Btw, the crowbar should blow the primary fuse. This is why it is critical to use rhe correct size and class of fuse. If the repeater had battery backup connected with the PSU, when the PSU goes off the battery voltage will feed back thru the pass transistors. You can install a diode in series with the output to prevent this..
Mr. J... The crow bar on my supplies have been set up with a contactor that drops a dead short across the mains line to sever the fuse when triggered instead of trying to hold a short until we can get to the unit, even to the point of tripping the breaker in the mains panel. This along with an installed 20 volt MOV on the output for effective equipment protection. All power supplies in one way or another lack proper engineering to cover all types of fails. Thanks Ray N S.C.
I hadn't thought about having a crowbar trigger something on the mains side of things. The National Electric Code use to and UL certification still does prohibit equipment that deliberately causes over current conditions on the mains or primary, so it isn't something a manufacturer could do. Probably one of those "don't try this at home" kind of things. :-)
The crowbar in an Astron power supply does no less than to short and load the unit as a whole but you can also short the output on the transformer secondary on the 35 amp and bigger power supplies and get the same effect however would not try this on lower current(20 amp and below) power supplies. It has been helpful to us both ways. Great video too. Ray n S.C.
Astron, Pyramid etc. These are all cheap PSUs and the Astron and Pyramid circuits are almost identical. Both using an LM723 with a driver transistor driving the pass transistors.
If using at a remote site, I would have a shutoff device that triggers at a specified V or A. The astron is a great supply, but it doesn't babysit itself.
The 723 has foldback current limiting, and the short circuit current on mine is just 1A when the crowbar trips.
5 років тому+1
I would just say I have repaired many of these, when the SCR clamps it's supposed to blow the primary fuse, Iv'e never seen one with the proper size fuse do any damage to the power supply, it's a good idea, I'd rather toast the power supply than a radio that cost a thousand dollars, I added the SCR to my personal supply on the bench, and the only problem after 20 years was a short in the rectifier, not bad, I hardly shut it off. for the money about the best linear supply you can buy.
Schematically, Astron supplies are pretty good. BUT, the way that they are built includes sky-wiring, and marginal transformer designs. The PC boards are supported by the filter capacitor and working on them is a real pain. NONE of the primary supply connections have protective heat shrink on them either, so BE CAREFUL working on them. Consider them home brew supplies.
I'm working on a RS-35M the problem may be a result of the "in-rush current" just about every time I turn it on there is a (Bang! or Thud!) Sound. Now after using it very casually over the past 5 years mainly for monitoring and not so much for transmitting (meaning low current draw all those years) The unit will not turn on correctly anymore it "cycles" on/off sort of before it will stay on. This past week it finally stopped doing that and now it just endlessly cycles on/off, by this I mean the meters go low than up, then low than up, over and over again and it will not reach or stay where the meters should be. I assume that it's the "crow-bar" protection and will use some of your troubleshooting advice to locate the problem.
The thud may be the capacitors charging, but it could be something like the crowbar shorting a temporary over voltage condition. I would get a spare LM723 and check that by replacement. The regulator ICs are getting old in a lot of these and seem prone to failure.
UPDATE: Don't over complicate things lol. What I mean by this is I took most of everything apart only to discover it was a (burning out) but not yet fully burnt out on/off switch! I should have started there but it was not easy to tell until I took it completely apart and seen the inside damage (melt down/apart) It's one of those orange back lit switches. Not sure what happened to it if it's the bulb that cause it to over heat and meal or the soldered wire on the connection area (only one was soldered the others were clipped on). All the while I was thinking something much more complicated like the IC or bad Transistor on the back. Now that I've replaced the switch with a simple non-lit on/off switch and tapped up the wire not being used for the light just in case I ever want to go with that type of switch again, it's working with no problem at all. For sure it was the on/off switch that it came with from the store. Thanks for the tip's advice and comments everyone. I believe I should find some extra parts just in case I ever need them!
I have an RS-35A that’s not working. When I turn it on, there is no output voltage and the heat sink gets very hot after about 3 min upon switching on. What could be the issue? It’s an old model the transistors manufacture numbers are 8644. Unfortunately the serial numbers stickers were removed.
First thing would be a really good visual inspection to see if anything looks bad (scorched or physical damage.) I'd disconnect the crowbar circuit first, but I would tend to suspect either the regulator IC or maybe a failed (shorted) pass transistor. I'd pull the transistors second if the crowbar didn't change anything. Then I'd replace the IC. It could be a capacitor that has shorted also. After that, it's pretty much going through component by component looking for the issue.
@@W4JBM thanks for your reply. I cleaned/ replaced silicone paste and tested the pass transistors and I think they are all good- I get 0.48 V to 0.49V when diode testing. Also it doesn’t get hot anymore. However I still don’t get 13.8Vdc instead only get 0.89 Vdc. I’ll check the individual components next and also try to disconnect the purple wire to the crowbar. Thanks hopefully I get to fix it soon!
Hi. I have a Astron RM-12A. It has a power switch on the front that kinda flickers. Any thoughts on what could cause this and if it will be an issue? Asking because I had the supply randomly turn off. I unplugged it and waited plugged it back in and it works again. Appreciate any insight you can give.
It looks like the same switch they use on other supplies which has a 120 VAC bulb built into the switch. I'm assuming it is probably a neon bulb and suspect the flickering is not related to the issue. I'd probably replace the UA723 regulator IC first because they are cheap and it is socketed. Is it under load when it fails? I'd tend to put it on some type of dummy load (a resistor bank if you have one) because there is a reasonable chance the crowbar circuit is kicking in and shorting the output (and if the crowbar itself fails at some point, you might put the full unregulated voltage onto whatever you're powering with it). If it is lightly loaded, you could pull one pass transistor at a time and see if the problem goes away--but even then you really can't be sure it is the pass transistor that is the root cause. It starting getting into good old fashioned trial-and-error trouble shooting at that point.
My 35m astron will just ( audible click ) and drop voltage to 0. It does it when I have been using moderate amps on fm modes. It does it at 12 amps. Thats low current for a 27 amp continuous duty rating. The gauge lights stay lit, just no power out. I turn it off and its fine,,, Not sure whats going on. I can run it at 100 watts fm and draw 20 to 22 amps with no issues, just seems the extended use trips something. I can still lay hands on heat sink, hot but doable with bare skin. I know enough to know I don't know enough to fix it.
1958johndeere620 If it drops voltage, but the current pegs, that is likely an issue in the crowbar. It sounds like you are dropping voltage and current though. My first thought would be to replace the 723 regulator IC. With age and a few voltage spikes, they can act up. The other thing I'd check is that the pass transistors are roughly the same warmth. I've seen these look okay with one of the pass transistors doing all the work because of a bad transistor or an out of tolerance balancing resistor. But my gut says the regulator IC.
@@W4JBM It feels the 4 pass transistors are the same. I put it in fm mode and cranked 100 watts and keyed down. It takes the 20 amps fine, the transistors get pretty warm quick at that amp level and they all feel close in temp. The voltage and amps drop to 0. Turn off and right back on, and all is good. It does seem to happen with extended use, the heat sink pretty warm, yet not taxing the unit hard. It has always clicked off when I was receiving and not transmitting during an extended qso. It did this once and a great while since new. Its now 3 years old, limited use, shut off and covered 95% of the time. Here is a copy and paste email I got directly from Astron,,,,, Word for word, no grammar corrections " Firt check that the AC snd DC grounds are well tight to chassis. 2. Please check if there is a .1mf capacitor at SCR1 from gate to cathode. It id s little yellow Cap. On top of the control board. If it is missing Lets add it. If loose lets resolder it, " I have the schematics yet can't seem to see what he is talking about. ( the .1mf capacitor at SCR1 ) I am NOT a good electronics guru. I did find a bad solder on one resistor in the board. Actually a totally missed solder joint, just the tip through the board and no solder. I soldered it, yet have not taxed the ole girl yet to see if it fixed it. I know the 723 is a plug and play so that may be an easy fix for me to try too. AND many thanks for the reply..
Astron is simple and well documented. 'nuff said
Btw, the crowbar should blow the primary fuse. This is why it is critical to use rhe correct size and class of fuse.
If the repeater had battery backup connected with the PSU, when the PSU goes off the battery voltage will feed back thru the pass transistors. You can install a diode in series with the output to prevent this..
Mr. J... The crow bar on my supplies have been set up with a contactor that drops a dead short across the mains line to sever the fuse when triggered instead of trying to hold a short until we can get to the unit, even to the point of tripping the breaker in the mains panel. This along with an installed 20 volt MOV on the output for effective equipment protection. All power supplies in one way or another lack proper engineering to cover all types of fails.
Thanks
Ray N S.C.
I hadn't thought about having a crowbar trigger something on the mains side of things. The National Electric Code use to and UL certification still does prohibit equipment that deliberately causes over current conditions on the mains or primary, so it isn't something a manufacturer could do. Probably one of those "don't try this at home" kind of things. :-)
The crowbar in an Astron power supply does no less than to short and load the unit as a whole but you can also short the output on the transformer secondary on the 35 amp and bigger power supplies and get the same effect however would not try this on lower current(20 amp and below) power supplies. It has been helpful to us both ways. Great video too.
Ray n S.C.
Astron, Pyramid etc. These are all cheap PSUs and the Astron and Pyramid circuits are almost identical. Both using an LM723 with a driver transistor driving the pass transistors.
If using at a remote site, I would have a shutoff device that triggers at a specified V or A. The astron is a great supply, but it doesn't babysit itself.
The 723 has foldback current limiting, and the short circuit current on mine is just 1A when the crowbar trips.
I would just say I have repaired many of these, when the SCR clamps it's supposed to blow the primary fuse, Iv'e never seen one with the proper size fuse do any damage to the power supply, it's a good idea, I'd rather toast the power supply than a radio that cost a thousand dollars, I added the SCR to my personal supply on the bench, and the only problem after 20 years was a short in the rectifier, not bad, I hardly shut it off. for the money about the best linear supply you can buy.
What causes voltage drop when on load
Nice video Jim
I have had to repair mine a few tis over the years.
They are great supplies, but can definitely use the occasional bit of TLC.
Schematically, Astron supplies are pretty good. BUT, the way that they are built includes sky-wiring, and marginal transformer designs. The PC boards are supported by the filter capacitor and working on them is a real pain. NONE of the primary supply connections have protective heat shrink on them either, so BE CAREFUL working on them. Consider them home brew supplies.
I'm working on a RS-35M the problem may be a result of the "in-rush current" just about every time I turn it on there is a (Bang! or Thud!) Sound. Now after using it very casually over the past 5 years mainly for monitoring and not so much for transmitting (meaning low current draw all those years) The unit will not turn on correctly anymore it "cycles" on/off sort of before it will stay on. This past week it finally stopped doing that and now it just endlessly cycles on/off, by this I mean the meters go low than up, then low than up, over and over again and it will not reach or stay where the meters should be. I assume that it's the "crow-bar" protection and will use some of your troubleshooting advice to locate the problem.
The thud may be the capacitors charging, but it could be something like the crowbar shorting a temporary over voltage condition. I would get a spare LM723 and check that by replacement. The regulator ICs are getting old in a lot of these and seem prone to failure.
UPDATE: Don't over complicate things lol. What I mean by this is I took most of everything apart only to discover it was a (burning out) but not yet fully burnt out on/off switch! I should have started there but it was not easy to tell until I took it completely apart and seen the inside damage (melt down/apart) It's one of those orange back lit switches. Not sure what happened to it if it's the bulb that cause it to over heat and meal or the soldered wire on the connection area (only one was soldered the others were clipped on). All the while I was thinking something much more complicated like the IC or bad Transistor on the back. Now that I've replaced the switch with a simple non-lit on/off switch and tapped up the wire not being used for the light just in case I ever want to go with that type of switch again, it's working with no problem at all. For sure it was the on/off switch that it came with from the store. Thanks for the tip's advice and comments everyone. I believe I should find some extra parts just in case I ever need them!
I have an RS-35A that’s not working. When I turn it on, there is no output voltage and the heat sink gets very hot after about 3 min upon switching on. What could be the issue? It’s an old model the transistors manufacture numbers are 8644. Unfortunately the serial numbers stickers were removed.
First thing would be a really good visual inspection to see if anything looks bad (scorched or physical damage.) I'd disconnect the crowbar circuit first, but I would tend to suspect either the regulator IC or maybe a failed (shorted) pass transistor. I'd pull the transistors second if the crowbar didn't change anything. Then I'd replace the IC. It could be a capacitor that has shorted also. After that, it's pretty much going through component by component looking for the issue.
@@W4JBM thanks for your reply. I cleaned/ replaced silicone paste and tested the pass transistors and I think they are all good- I get 0.48 V to 0.49V when diode testing. Also it doesn’t get hot anymore. However I still don’t get 13.8Vdc instead only get 0.89 Vdc. I’ll check the individual components next and also try to disconnect the purple wire to the crowbar. Thanks hopefully I get to fix it soon!
Hi. I have a Astron RM-12A. It has a power switch on the front that kinda flickers. Any thoughts on what could cause this and if it will be an issue? Asking because I had the supply randomly turn off. I unplugged it and waited plugged it back in and it works again. Appreciate any insight you can give.
It looks like the same switch they use on other supplies which has a 120 VAC bulb built into the switch. I'm assuming it is probably a neon bulb and suspect the flickering is not related to the issue. I'd probably replace the UA723 regulator IC first because they are cheap and it is socketed. Is it under load when it fails? I'd tend to put it on some type of dummy load (a resistor bank if you have one) because there is a reasonable chance the crowbar circuit is kicking in and shorting the output (and if the crowbar itself fails at some point, you might put the full unregulated voltage onto whatever you're powering with it). If it is lightly loaded, you could pull one pass transistor at a time and see if the problem goes away--but even then you really can't be sure it is the pass transistor that is the root cause. It starting getting into good old fashioned trial-and-error trouble shooting at that point.
me too thanks for sharing
Thanks, I learned a lot.😀
My 35m astron will just ( audible click ) and drop voltage to 0. It does it when I have been using moderate amps on fm modes. It does it at 12 amps. Thats low current for a 27 amp continuous duty rating. The gauge lights stay lit, just no power out. I turn it off and its fine,,, Not sure whats going on. I can run it at 100 watts fm and draw 20 to 22 amps with no issues, just seems the extended use trips something. I can still lay hands on heat sink, hot but doable with bare skin. I know enough to know I don't know enough to fix it.
1958johndeere620 If it drops voltage, but the current pegs, that is likely an issue in the crowbar. It sounds like you are dropping voltage and current though. My first thought would be to replace the 723 regulator IC. With age and a few voltage spikes, they can act up. The other thing I'd check is that the pass transistors are roughly the same warmth. I've seen these look okay with one of the pass transistors doing all the work because of a bad transistor or an out of tolerance balancing resistor. But my gut says the regulator IC.
@@W4JBM It feels the 4 pass transistors are the same. I put it in fm mode and cranked 100 watts and keyed down. It takes the 20 amps fine, the transistors get pretty warm quick at that amp level and they all feel close in temp. The voltage and amps drop to 0. Turn off and right back on, and all is good. It does seem to happen with extended use, the heat sink pretty warm, yet not taxing the unit hard. It has always clicked off when I was receiving and not transmitting during an extended qso. It did this once and a great while since new. Its now 3 years old, limited use, shut off and covered 95% of the time. Here is a copy and paste email I got directly from Astron,,,,, Word for word, no grammar corrections " Firt check that the AC snd DC grounds are well tight to chassis.
2. Please check if there is a .1mf capacitor at SCR1 from gate to cathode. It id s little yellow
Cap. On top of the control board. If it is missing
Lets add it. If loose lets resolder it,
"
I have the schematics yet can't seem to see what he is talking about. ( the .1mf capacitor at SCR1 ) I am NOT a good electronics guru. I did find a bad solder on one resistor in the board. Actually a totally missed solder joint, just the tip through the board and no solder. I soldered it, yet have not taxed the ole girl yet to see if it fixed it. I know the 723 is a plug and play so that may be an easy fix for me to try too. AND many thanks for the reply..
👀 👍
Take the ums and uhs out and this video would be 5 minutes shorter