Replacing MicroVAX II PSU With a Modern PSU

Robert Jarratt robert.jarratt at
Wed Nov 25 12:46:06 CST 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Jon Elson
> Sent: 25 November 2015 17:10
> To: General at; Discussion at and Off-
> Topic Posts
> Subject: Re: Replacing MicroVAX II PSU With a Modern PSU
> On 11/25/2015 11:01 AM, Robert Jarratt wrote:
> > My reading of the Qbus spec is that P OK and DC OK are active high.
> > That diagram tells me that both control signals are driven the same
> > way because the two circuits are identical except for the timing caps.
> > When the power is OK the output of the inverters is low, so the
> > transistors are off, presumably allowing the signals to float high.
> > When the power is not OK, the inverters are high, turning on the
> > transistors and shorting the signal to ground. But, I am no expert,
> > and could have interpreted those circuits all wrong. Regards Rob
> Yup, I read the circuit the same way.

Ah, I misread your earlier response, I thought you were saying something different.



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