Memory Voltage on MicroVAX II

Robert Jarratt robert.jarratt at
Sat Dec 5 18:18:06 CST 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Jon Elson
> Sent: 05 December 2015 23:40
> To: General at; Discussion at and Off-
> Topic Posts
> Subject: Re: Memory Voltage on MicroVAX II
> On 12/05/2015 01:49 PM, Robert Jarratt wrote:
> > As the 5V seems fine, the ripple seemed to be about 20mV (although I
> > am going to check again), I do wonder what could be causing the memory
> > modules to appear to be failing. I am hoping that re-seating will cure
> > it. Regards Rob
> I ran a uVAX-II for 21 years here in my house.  It was HOT STUFF when I
> got it in 1986!  By 2007, it was the slowest computer in the house.  It
> continuously during that period (at the end, it was only running a home
> environmental monitoring program, or I would have shut it down earlier.)
> Anyway, after some years of flawless operation, I started getting crashes
> every couple months.  When it would hang, I would power down and re-seat
> all the boards.  It seems like it was usually a failure of one of the
grant chains
> (either interrupt or DMA) and the disk controller would not be able to
> transfer.  Every once in a while I'd pull all the boards and vacuum out
> backplane and gently vacuum off the boards.  That sort of helped, maybe.
> The external UVII memory also had ribbon cables across the boards. Rough
> handling of these cables can cause intermittents.
> Jon

Yes, when I took the board out I noticed that the connector of the ribbon
was not fully inserted, although it seemed solid enough. So when I put it
all back together, I really made sure that the board was fully seated and
the ribbon cable connectors fully pressed home. I'll make doubly sure of
this in future. For anyone else's reference, this led to SCBINT errors from
the console firmware while trying to boot.



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