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Author Topic: Power supply schematic  (Read 824 times)
K6MA
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Posts: 5




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« on: March 14, 2011, 01:03:21 PM »

I purchased a bench power supply, Electro Industries model 3002A, from a ham at a swap meet. It was supposed to be working but it is not. Does anyone have a schematic for this? Contacting the manufacturer, who was very helpful, I found out that my power supply is very old using only transistors and no IC's. They no longer make this product with just transistors but make a newer version with IC's. They gave me the schematic for the newer model but it is of no use as mine is so old they did not keep any schematics for it. I would appreciate hearing from anyone with a schematic. My email address is: twiffer@roadrunner.com
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KA5N
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Posts: 4380




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« Reply #1 on: March 14, 2011, 01:24:02 PM »

Switching or linear??  If it is a linear supply you can reverse engineer it and draw your own schematic.  You can easily tell if any of the semiconductors are open (rare) or shorted.  So you will have zener diodes, transistors (which may be NPN or PNP and may be silicon or germanium (good luck finding replacements) and some capacitors and rectifiers.
If it is a switching power supply, my advice is to use it as an actual boat anchor as you likely can't reverse engineer it (if you could you wouldn't need to post here) and the parts may only be available directly from OZ.  Switching supplies are intolerant of any but direct replacement parts.  If you don't get every bad part replaced before power is applied, the supply is likely to blow up again and all your work will be for naught.
Buy a new one or get a used linear Astron and enjoy.
Allen
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K0BG
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« Reply #2 on: March 14, 2011, 01:52:58 PM »

If it is this one http://www.electroindustries.net/specifications.php# (click the 3002A photo) it is linear. If it is, the pass transistor is a 2n3055. They're about $3 each. The driver looks very similar, but is really an adjustable voltage regulator. They do a funny trick to change the range with a zener, and it's not all that robust. Used to own two of them, and wouldn't have another.
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K6MA
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« Reply #3 on: March 14, 2011, 05:01:04 PM »

Thanks for the assistance and suggestions. It is indeed a linear power supply and I have detected at least one bad transistor (no base/emitter voltage). As it is very old I will probably replace the electrolytic capacitors too as they look a little worse for wear.

73,
Terry K6MA
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