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Daniël Oosterhuis

Quadra 700 Astec PSU - Bad caps or something else?

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As you might have recently seen, I've acquired a Quadra 700 that seemingly had a dead power supply. I've since done some more testing, and I'd like to know whether I just got a case of bad caps, or something more.


In the machine, when powering up, the speaker would make some pops, each spaced out a second or so, with the LED flickering with each one. I later noticed the PSU fan would also twitch during those pops.

I've taken out the power supply, and tried running it on its own by shorting pin 9 and 10, which makes this PSU turn on. It will loudly click every few seconds, with the fan trying to spin up inbetween clicks.

The voltage rails don't really get to go to full power, they swing around 3V (-3V on the -12V rail) while the PSU is forced on.


Reading on 68kMLA, I did see mentions of a diode that could cause the power supply to fail powering on, hence why I'm wondering if it's truly bad caps.

The PSU is a Astec AA15831. Has anyone here ever had that PSU with the same or similar behavior, and have you been able to diagnose/fix it? I'd love to get the original PSU going again, but if it's going to get too complex, I might do what others have done and retrofit it with a modern PSU. Thanks in advance for any help, tips and suggestions!

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