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Old 27th November 2008, 01:50 AM   #1
manaox2 is offline manaox2  United States
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Unhappy STEPS at 47V?

The 24V STEPS supply after being shipped to a new location outputs 47V DC without a load. The transformer shouldn't be able to put out more the 42V I would think, I have tested it though with two meters.

http://s122.photobucket.com/albums/o264/manaox2/STEPS/

The AC ripple measures 0.003V with the Fluke meter.

Resistors were measured with a cheap CEN-TECH meter:

R1 = 60 ohm
R2 = 100 ohm
R3 = 100 ohm
R4 = ~2 Kohm (value keeps rising, awkward to test from top, I waited until value went up to 1.75k Ohm)
R5 = 4.75 Kohm

R1 should be 1Mohm and R4 should be 2.0K ( resistor reads 2000 and measure indicated its right approximately), R5 at 2.2K. So R1 and R5 are not measuring properly for me.

I apologize if I am being annoyingly stupid here, I'm not very knowledgeable yet in DIY really.
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Old 27th November 2008, 05:00 AM   #2
dtproff is offline dtproff  United States
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Unfortunately I can't get to your picture from my office computer so it'll have to wait till I get home. It sound like it is peak charging. Try adding a load resitor to the output and see if it is then in spec.

Tony
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Old 27th November 2008, 06:33 AM   #3
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Sounds like your regulator isn't regulating. The transformer is a 2 x 15VAC with the secondaries in series. The secondaries will be over 15VAC unloaded, so 47VDC is definitely possible after rectification.
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Old 27th November 2008, 09:28 AM   #4
00940 is online now 00940  Belgium
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Are you checking the resistors in the circuit ? If yes, the measurements will be not be reliable at all.

Your lm317 seems to act as just a short. Is the lm317 isolated from the heatsink ? Would the heatsink be touching the "input" side of D2 ?

Also, did you try to adjust the trimmer "vset" ? If the trimmer has gone bad, the lm317 will probably not do anything.
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Old 30th November 2008, 03:52 AM   #5
manaox2 is offline manaox2  United States
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Thank you! I was checking the resistors while in circuit, thanks, that makes sense.

Its hard to tell, but I don't see any of that. The LM317 is isolated, but its had many hours on it, it could have gone bad. The VSET would not be that hard to replace as well.

I wouldn't know what to use as a load resistor, I don't have any for that purpose actually. Is there any easy way to check or would it just be easier to replace them in the circuit? I have a mouser order already in the works, so I can tack these on.

I'll check the amplifier it was plugged into when I make/find a suitable supply. If it hasn't had its opamps fried, I would bet it could be something like peak charging.
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