31316re: [midatlanticretro] DEC VT131 Fault Diagnosis
- Jun 17, 2013Jay West I believe, of cctalk fame has one
-------- Original Message --------
> From: "Mike Strange" <mjstrange@...>circuit level?
> Sent: Monday, June 17, 2013 8:58 AM
> To: firstname.lastname@example.org
> Subject: [midatlanticretro] DEC VT131 Fault Diagnosis
> Has anyone here any experience with a DEC VT131 terminal keyboard at
>VT131 spec; I am
> I appreciate that there are probably many implementations to achieve the
> interested in one that uses an 8039 microcontroller, 2716 program store,CD4028 column
> drivers and CD4051 row detection.row intermittently
> We have a very odd fault whereby every letter to the left of P on each
> fails to function; we have changed the relevant column driver 4028 andthe frequency of
> fails reduces.symptoms; the supply
> It cannot be the row detection as this would exhibit a different set of
> voltage from the display unit is fine and the drive signals to the CD4028are still present.
> Anyone seen this fault before?
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