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From: hanavin@udel.edu (Chuck Hanavin)
Newsgroups: sci.electronics
Subject: Re: Help! Zenith Z29 going bonkers
Keywords: Zenith Z29
Message-ID: <41667@nigel.ee.udel.edu>
Date: 14 Jan 91 18:05:17 GMT
References: <1991Jan12.210223.19162@fs7.ece.cmu.edu>
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In article <1991Jan12.210223.19162@fs7.ece.cmu.edu> tamal@cougar.ece.cmu.edu (Tamal Mukherjee) writes:
>Hi,
>
>After coming back from a short vacation, I noticed that all of a sudden,
>spurious characters were cropping up on my Z29 terminal.  When I type
>something over them they have a tendency to do one of the following:
>	- display the typed character in correct case
>	- display the typed character in the wrong case
>	- display the char whose ascii value is 15 less than that of the
>	  typed character.
>	- and so on...
>
>Also, these occur randomly all over the screen, making it difficult to use
>the terminal.  I believe that there is something wrong with some RAM 
>that stores the characters that are being currently displayed.  Does anyone
>have any ideas about fixing this ?

Replace U440, character ram chip. It is a static ram chip 6116 which
can be bought from jameco for 3 dollars.

While we are on the subject of z29's, here are a few other common problems.

Screen filled with strange characters (sometimes scrolling)
Check U417.

vertical sync off frequency, Check U407.

Has curser but terminal serial port not communicating, check + and - 12
volts on 7912 and 7812. If ok check U401 and U403.
the solder connection on the power supply board tends to deteriorate
with age.

Chuck (WB3FJJ)