I got a free Astron 50A linear 12V supply that blows it's 120V fuse at power-up. There is nothing connected to the supply, so this is an internal problem. I know these supplies aren't the best, but it was free because of the problem...so I am willing to spend some time and money to fix it.
I looked at repeater-builder, which makes mention of a failed diode bridge rectifier in 35A model, but I don't see these in the 50A model. What else should I be looking at for the failure point?
Astron RM-50M problem
Moderator: Queue Moderator
-
007
- Posts: 1546
- Joined: Sat Nov 23, 2002 5:22 am
- What radios do you own?: W7 FPP lowband MaraTrac w/AES
Astron RM-50M problem
Do not make Sig angry...he'll just keep ringing the bell.
Re: Astron RM-50M problem
I have one that has an annoying problem that if you turn the power switch on to slowly it will blow the circuit breaker. The supply works great other than this glitch.
Re: Astron RM-50M problem
Well, there HAS to be a rectifier in the supply somewhere, whether it's one or two bridges or two discrete diodes. Chances are high that one or both are defective. If it's not the diodes, the main filter capacitor could be shorted.
Use normal troubleshooting techniques: disconnect stuff and measure it with an ohm-meter. First go directly across the main filter capacitor, then disconnect the red wire going to it and measure the cap and the red wire to ground. Both should be hundreds of ohms in one direction, under 20 ohms in the other direction.
These two components are what usually causes the main fuse to blow.
Of course, the transformer could also be defective. That's NOT easy to come by; just go buy another supply.
Bob M.
Use normal troubleshooting techniques: disconnect stuff and measure it with an ohm-meter. First go directly across the main filter capacitor, then disconnect the red wire going to it and measure the cap and the red wire to ground. Both should be hundreds of ohms in one direction, under 20 ohms in the other direction.
These two components are what usually causes the main fuse to blow.
Of course, the transformer could also be defective. That's NOT easy to come by; just go buy another supply.
Bob M.
-
007
- Posts: 1546
- Joined: Sat Nov 23, 2002 5:22 am
- What radios do you own?: W7 FPP lowband MaraTrac w/AES
Re: Astron RM-50M problem
I'll get my DVM on the job and see what's what. Thanks for the heads-up.kcbooboo wrote:Well, there HAS to be a rectifier in the supply somewhere, whether it's one or two bridges or two discrete diodes. Chances are high that one or both are defective. If it's not the diodes, the main filter capacitor could be shorted.
Use normal troubleshooting techniques: disconnect stuff and measure it with an ohm-meter. First go directly across the main filter capacitor, then disconnect the red wire going to it and measure the cap and the red wire to ground. Both should be hundreds of ohms in one direction, under 20 ohms in the other direction.
These two components are what usually causes the main fuse to blow.
Of course, the transformer could also be defective. That's NOT easy to come by; just go buy another supply.
Bob M.
Do not make Sig angry...he'll just keep ringing the bell.
Re: Astron RM-50M problem
There are not that many things that can go wrong with those supplies. A few heads up on looking for a
problem.
1. Try lifting the output terminals from the chassis. I have seen these get over tightened and short to
ground.
2. Check out the surge protectors near the power input and switch. If the power line took a lightning hit,
it is not uncommon for these to short out.
3. Check the rectifier bridge. If one or two diodes short out, you will pull high current. You need to
lift the wires off the bridge to test it. Make a chart of where the different colored wires were attached.
4. You could have a shorted pass transistor. These can be tested with an Ohm meter. Again you may
have to lift a wire or two to check them properly. There are more than one pass transistor in your
power supply. You will need to check each one if it comes down to that.
As others have said, you just need to start walking through the package. Lift some wires and see
if the trouble goes away or stays. This will point you in the direction of the problem. I would start by
lifting the DC side of the bridge rectifier wires and going from there.
Jim
problem.
1. Try lifting the output terminals from the chassis. I have seen these get over tightened and short to
ground.
2. Check out the surge protectors near the power input and switch. If the power line took a lightning hit,
it is not uncommon for these to short out.
3. Check the rectifier bridge. If one or two diodes short out, you will pull high current. You need to
lift the wires off the bridge to test it. Make a chart of where the different colored wires were attached.
4. You could have a shorted pass transistor. These can be tested with an Ohm meter. Again you may
have to lift a wire or two to check them properly. There are more than one pass transistor in your
power supply. You will need to check each one if it comes down to that.
As others have said, you just need to start walking through the package. Lift some wires and see
if the trouble goes away or stays. This will point you in the direction of the problem. I would start by
lifting the DC side of the bridge rectifier wires and going from there.
Jim
007 wrote:I got a free Astron 50A linear 12V supply that blows it's 120V fuse at power-up. There is nothing connected to the supply, so this is an internal problem. I know these supplies aren't the best, but it was free because of the problem...so I am willing to spend some time and money to fix it.
I looked at repeater-builder, which makes mention of a failed diode bridge rectifier in 35A model, but I don't see these in the 50A model. What else should I be looking at for the failure point?
Re: Astron RM-50M problem
The rectifier in an RM-50 is two stud-mount diodes on a small heatsink on the back of the cabinet. This supply has an electronic over-current shutdown and an over-voltage "crowbar" on the output. If this supply has had lightning damage, there could be a failure (shorted pass transistor) that causes a high output voltage, and if there is also failure in the over-current protection, the output crowbar may be what is blowing the A/C fuse. The SCR that is used in the crowbar circuit is also prone to shorting out, so if there is a failure in the over-current protection, a shorted SCR would blow the fuse. The LM-317 regulator IC is also pretty prone to failure. It is in a socket, and really cheap, so when I work on an Astron supply, I'll replace it before I do anything else.
Hope this gives you some help,
Kevin
Hope this gives you some help,
Kevin
Re: Astron RM-50M problem
The circuit diagrams on repeater-builder are pretty much the same circuit for the 20A, 35A and 50A versions.
Easy to check the pass transistors, remove the two mounting screws in each transistor, that disconnects the collector from the rest of the circuit.
Measure each one with an ohm meter emitter to collector, + on the collector, - on the emitter.
Easy to check the pass transistors, remove the two mounting screws in each transistor, that disconnects the collector from the rest of the circuit.
Measure each one with an ohm meter emitter to collector, + on the collector, - on the emitter.