Loading ...
Sorry, an error occurred while loading the content.

DEC VT131 Fault Diagnosis

Expand Messages
  • Mike Strange
    Has anyone here any experience with a DEC VT131 terminal keyboard at circuit level? I appreciate that there are probably many implementations to achieve the
    Message 1 of 2 , Jun 17, 2013
    • 0 Attachment
      Has anyone here any experience with a DEC VT131 terminal keyboard at circuit level?

      I appreciate that there are probably many implementations to achieve the VT131 spec; I am interested in one that uses an 8039 microcontroller, 2716 program store, CD4028 column drivers and CD4051 row detection.

      We have a very odd fault whereby every letter to the left of P on each row intermittently fails to function; we have changed the relevant column driver 4028 and the frequency of fails reduces. 

      It cannot be the row detection as this would exhibit a different set of symptoms; the supply voltage from the display unit is fine and the drive signals to the CD4028 are still present.

      Anyone seen this fault before?

      Regards,
      Mike

       
    • B. Degnan
      Jay West I believe, of cctalk fame has one bd ... circuit level? ... VT131 spec; I am ... CD4028 column ... row intermittently ... the frequency of ...
      Message 2 of 2 , Jun 17, 2013
      • 0 Attachment
        Jay West I believe, of cctalk fame has one
        bd



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