UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

TonyDuell · 27th Jul 2018, 7:38 pm

Where does the '12V' line on your circuit come from? A rectifier on the chopper transformer? If so, it will not be present until the PSU is running.

I don't think it's an over-voltage shutdown at all. What it seems to be doing is preventing the PSU from starting until the voltage across the mains smoothing capacitors (the '340V' in the diagram I assume) is high enough for Q10 to turn on, thus pulling shutdown high. At this point the PSU rattles into life, the 12V line comes up and keeps the supply running no matter what Q10 does.

27th Jul 2018, 7:38 pm	#8
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,224	Re: Gould 4072 bad PSU Where does the '12V' line on your circuit come from? A rectifier on the chopper transformer? If so, it will not be present until the PSU is running. I don't think it's an over-voltage shutdown at all. What it seems to be doing is preventing the PSU from starting until the voltage across the mains smoothing capacitors (the '340V' in the diagram I assume) is high enough for Q10 to turn on, thus pulling shutdown high. At this point the PSU rattles into life, the 12V line comes up and keeps the supply running no matter what Q10 does.