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Question about DC power supply

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  #9  
Old 02-11-2012, 07:04 AM
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Quote:
Originally Posted by Okiksapa View Post
That totally makes sense now that I think about it. I'm concerned about the voltage, though. I just want to make sure all is working before I hook anything up to it, but guess I need to hook something up to put a load on it. How about the voltage, anything I can hook up to that I might have laying around to check out the unit? Thanks.
Do you have a volt/ohm meter? if it supposed to show voltage as Beetle says then this meter would indicate voltage output even if the unit's meter does not as far as testing with something laying around you can use anything that requires dc voltage in the range of the power supply, just make sure of the the polarity is correct before tuning on the power supply.

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Old 02-11-2012, 07:06 AM
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Here's what I have so far on this:

1. Fuse is okay
2. DC adjustment knob was loose, tightened that.
3. Hooked up DVM to it and got that following:
- 1.86-1.89 VDC no matter where the voltage adjustment knob was

So - does it look like my voltage adjustment circuitry is bad? It seems so to me. If so, where do I begin to troubleshoot this? What do I test with the DVM? What parts might I need? I'm assuming it will need some soldering to get this fixed.

I appreciate your advice and assistance with this.

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Old 02-11-2012, 08:32 AM
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I hooked up DVM again and took off the cover to look around.

Nothing seems loose or broken inside.

I did notice that when I rotate the voltage adjustment knob that the DV volts drop from 1.89 to 1.86 when I rotate clockwise. That seems strange, as the volts should increase.
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  #12  
Old 02-11-2012, 11:04 AM
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Quote:
Originally Posted by Okiksapa View Post
Here's what I have so far on this:

1. Fuse is okay
2. DC adjustment knob was loose, tightened that.
3. Hooked up DVM to it and got that following:
- 1.86-1.89 VDC no matter where the voltage adjustment knob was

So - does it look like my voltage adjustment circuitry is bad? It seems so to me. If so, where do I begin to troubleshoot this? What do I test with the DVM? What parts might I need? I'm assuming it will need some soldering to get this fixed.

I appreciate your advice and assistance with this.
Quote:
Originally Posted by Okiksapa View Post
I hooked up DVM again and took off the cover to look around.

Nothing seems loose or broken inside.

I did notice that when I rotate the voltage adjustment knob that the DV volts drop from 1.89 to 1.86 when I rotate clockwise. That seems strange, as the volts should increase.

Sounds to me like the voltage regulator chip is shot. When the voltage regulator takes a dump the typical output voltage is around 2 volts which is what you are seeing. I am pretty sure you need a new LM723 regulator chip. Either that or one of the pass transistors on the heat sink is shorted and allowing too high a voltage to appear on the output and the safety protection is constantly being tripped which limits the output to jst a volt or two. An LM723 regulator chip is just a couple dollars and plugs into a socket and would be easy to replace. The transistor however is a bit harder but not difficult IF you are familiar with electronics.
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Old 02-11-2012, 12:24 PM
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Quote:
Originally Posted by Captain Kilowatt View Post
Sounds to me like the voltage regulator chip is shot. When the voltage regulator takes a dump the typical output voltage is around 2 volts which is what you are seeing. I am pretty sure you need a new LM723 regulator chip. Either that or one of the pass transistors on the heat sink is shorted and allowing too high a voltage to appear on the output and the safety protection is constantly being tripped which limits the output to jst a volt or two. An LM723 regulator chip is just a couple dollars and plugs into a socket and would be easy to replace. The transistor however is a bit harder but not difficult IF you are familiar with electronics.
I did not know there was a dual in line package version of this chip, I have used the metal can package which I have a extra or 2 of if needed.

http://www.ti.com/lit/ds/symlink/lm723.pdf

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  #14  
Old 02-11-2012, 01:47 PM
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Originally Posted by mackmobile43 View Post
I did not know there was a dual in line package version of this chip, I have used the metal can package which I have a extra or 2 of if needed.

http://www.ti.com/lit/ds/symlink/lm723.pdf

Man where have you been? I have a Tripp Lite power supply that must be at close to 20 years old and it has the DIP package style in it. You need to get out more often Mack.
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Old 02-11-2012, 02:27 PM
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Quote:
Originally Posted by Captain Kilowatt View Post
Man where have you been? I have a Tripp Lite power supply that must be at close to 20 years old and it has the DIP package style in it. You need to get out more often Mack.
The only use I've had for the lm-723 was in a bias circuit and never had to open any of my power supplies for servicing so that's why I was surprised, to too have a Tripp Lite now you make me want to tear into it and touch the guts.

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Old 02-11-2012, 02:45 PM
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Here's what I've done now:

Per the advice of the guy I bought this from -

1. I jumped the two 'outside' wires on the voltage adjustment knob on the inside of the case.
2. When I did this, I was able to adjust the voltage all the way up to 14.97 VDC.
3. However, when I reached a little over the halfway point on turning the knob, the voltage started to drop back down.

The guy I bought it from thinks the adjustment knob 'pot' is bad. There are three wires going to the knob, and all three are connected to the inside of the knob. I'll check the connection on the board later. It's putting out the correct voltage, I'm just unable to adjust it up where it needs to be without jumping the knob wires.
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