Replacing broken Astron ® or Pyramid ® regulator boards

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Replacing Astron®, Pyramid® and others regulator board

First......cut out the existing regulator board leaving all the wires as long as possible.

Find a place in the unit to mount an 2N3055 transistor. It does not need much, if any, heat sink. But it must be mounted so that it is not grounded to any part of the case. I have used double sided stick tape like used in window glazing. This 2N3055 will be used to be driven by the 723 regulator board and in turn to drive the pass transistor array of your existing unit.

Wire the whole power supply like: this.

Build an current limiting array per this page's suggestions. Connect the current limiting array in series with the positive output of the unit. You will later be connecting the current limit and current sensing circuits from the regulator board on each side of the array.

Find a spot within to mount the new regulator board so that there is noting touching it from within. You can mount it on a mini-"L" bracket that you can make out of any piece of light weight aluminum.

Connect the "CL" or current limit wire from the regulator board to the power supply side of the current limiting array. Then connect the "CS" or current sense from the regulator board to the positive out put side of the current limiting array.

Connect the "Vo" or voltage out from the regulator board to the "base" pin of the 2N3055 drive transistor. Then connect the "emitter" pin of the 2N3055 to the bases of all the pass transistors. Connect the case or the "collector" of the 2N3055 to the collectors of the pass transistors or the positive of the main filter capacitor bank.

Connect the "-" or negative of the regulator board to the negative side of the main filter capacitor.

Connect the "AC/AC" wires from the regulator board to the AC secondary of the transformer. I use only half of the transformer. In other words: One wire goes to the center tap of the secondary and the other wire connects to one side of the AC secondary. This way there is enough "voltage reference" but not too much for the regulator board to be able to regulate. I have found that this helps prevent the 723 from being destroyed by keeping it's reference voltage low.

The manufacturer of the 723 says that it can handle 40 volts. However, it you get the voltage up higher than half of the transformer, there is no consideration for a voltage spike that can really push up the voltage. In that case, you end up with a toasted 723 voltage regulator.

This should get you on the way to a good working assembly. It is just the basics and some of it will be up to the individual and their own preferences and techniques.

Good Luck and dont' let the smoke out !

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