MicroVAX II Console Garbling Characters

Rob Jarratt robert.jarratt at ntlworld.com
Wed Aug 24 11:05:51 CDT 2016

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Mouse
> Sent: 24 August 2016 16:35
> To: cctalk at classiccmp.org
> Subject: Re: MicroVAX II Console Garbling Characters
> >> I have a MicroVAX II which has started garbling and losing characters
> >> output to the console.  [...]
> > Iâ??ve seen similar  with under two occasions.  [...]
> Furthermore, "garbling" is horribly imprecise.

Fair enough, let me see if I can answer more precisely.

> If certain characters always get corrupted, and a given character always
> corrupted to the same thing?

No, the corruption appears to be random. Unfortunately I don't have a
protocol analyser to help, but I could try to get a log using Putty
connecting via a DECserver 90M. I will try that later.

> If it's always the same characters getting corrupted, but they get
> to different things on different occasions?
> If there's no uniformity on which characters get corrupted, but a given
> character, if corrupted, always gets corrupted to the same thing?
> If both which characters get corrupted and what they get converted into
> show no consistency?

Regarding all the above, it looks pretty random to me, but I will try to get
a dump of the characters and compare with what they should be.

> Each of those scenarios points towards a different constellation of
> causes.  (Furthermore "same characters" can be taken either of two ways,
> either "characters with the same bit pattern, regardless of where they
> or "characters at the same place in the output, regardless of bit
pattern".  It
> could even be a cross between those.)
> Similar remarks apply to "losing".

Well, it does "lose" characters. It seems to be that after a short burst of
characters it just gives up and I don't see anymore characters for a while,
then it will show a few more after a bit of a pause (but not always).

> The post also said
> >> It had seemed that re-seating the processor board would fix it, but
> >> that no longer seems to be the case.
> It occurs to me that it might not have been the re-seating that was
> responsible, but something else incidental to that.  For example, if the
> problem is thermal, powering it off briefly might have helped; if (to
> that theory) if the environment has been getting hotter, it may be that
> leaving it off briefly now doesn't cool it enough.

Unfortunately this happens both with the machine cold and warm.

> Without more details, we can't really do much but take stabs in the dark.

I will try to get more info.

Incidentally, the terminal and the machine *were* plugged into different
sockets, but now they are connected to the same wall socket and the problem



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