Is there some way to tell? Any help would be appreciated. Thanks Ron. NT4W , Jan 9, I would check the SCR for a short crowbar protection and Z1 16 volt zener for short. Possible crowbar protection circuit kicked in and shorted the output and opened up the pass transistors. Possibility of RF caused crowbar to kick in. Should have opened line fuse. Check if that is the correct amperage. I would use 2n for the replacement pass transistors. If it were mine I would replace the pass transistors first 2N and temporarly remove the crowbar SCR and see what the voltage output is.
Sometimes RF feedback into power supply will cause problems. Once working I would also add RF bypass caps to the output terminals of the power supply.
After repair remember to put the crowbar SCR back in circuit. The crowbar circuit works by shorting the PS output terminals if voltage from pass transistors exceeds 16 volts and turns on the crowbar SCR turning on and preventing excessive voltage from power supply ruining anything connected to the power supply from overvoltage caused by shorted pass transistors.
The unregulated, rectified voltage from the transformer is usually around volts. If the protection crowbar circuit kicked in that may have destroyed the pass transistors. Last edited: Jan 10, N8VIL , Jan 10, I have heard of more than 1 ham having problems with that supply.
One was the club president when I was back in Dayton. Seems like the biggest problem with them is that they are Pyramid supplies By the parts listed, it sounds like it has a lot of parts common with Astron. Maybe a little reading here will give you some Ideas Repeater Builders has the 3-page product sheet, with Schematic Diagram. Scroll down to see transistor table. W9GB , Jan 10, Thanks a lot for your replies guys. All of this will help a lot. I have ordered the 2N's.
I see that there quite a few other things I should check, so I will get busy on that. The fuse did not blow and the fuse was the correct amperage. Go figure. Pyramid ammeters measure the voltage drop across a single shunt resistor in series with the positive output, whereas Astron ammeters measure the drop across one of the series-pass transistor emitter balancing resistors.
This makes the Pyramid ammeter track the actual load current much more accurately, especially if one of the series-pass transistors fails. The numerical value in the model number indicates the peak intermittent current capability. Some model numbers have "K" for the suffix while others have "KX". The support group told me "PS-nnK supplies are the older version. The updated version assembled by our new factory is PS-nnKX.
The boards and features are different but both models share the same specs. Some supplies always have meters while others never do. Don't be surprised if your unit's parts values and even connections do not agree with the schematic.
They made lots of changes and documentation upkeep was apparently not a priority. If anybody has manuals as PDF files or hard-copy that can be scanned for models that we do NOT have, please consider sending them in to the page maintainer listed at the top of this page so they can be added. Has schematic but no parts values. Has schematic with parts values.
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