Tektronix 4051 repair.

Mattis Lind mattislind at gmail.com
Thu Sep 22 03:17:22 CDT 2016

2016-09-21 22:27 GMT+02:00 Pete Lancashire <pete at petelancashire.com
<javascript:_e(%7B%7D,'cvml','pete at petelancashire.com');>>:

> They look pretty bright to me for a DVST screen. Your problem looks
> 'analog', check the character blanking is working, then check the digital
> to analog, deflection etc.

I cannot find anything mentioned about character blanking in the circuit

I read this on the topic "Alphanumeric Display":

"Refer to the display control block diagram (Fig 6-13). The display
coordinate position is generated through the digital-to-analog converters
(X DAC and Y DAC) and fed through the filter circuitry with the filtering
disabled. A short time later, either SOT is activated to print a cursor
refresh dot or ADOT is activated to print a character dot. The timers for
cursor intensity and character intensity are adjustable by potentiometers
accessible through the bottom of the assembled instrument."

Maybe this is the "A short time later" that it is not working since seems
to draw instantly. But as far as In understand that timer is generated in
the digital parts.

Note that this is not a computer or terminal. It is an instrument per
Tektronix definition...

Unfortunately the detailedness of the circuit description is not up to the
DEC standards in my opinion. There are no scope diagrams describing the
pulses going to the Z-axis as far as I can see which is unfortunate.


> When you hit the erase what happens ?
> -pete
> On Wed, Sep 21, 2016 at 12:07 PM, Mattis Lind <mattislind at gmail.com
> <javascript:_e(%7B%7D,'cvml','mattislind at gmail.com');>> wrote:
> > I took a look at the Tektronix 4051 that we got a few years back. After
> > checking the PSU I turned it on and it seemed to start up fine. The
> machine
> > responded well to the keypresses but it was hardly readable on the
> screen.
> >
> > Anyone that can give advice on what is wrong and how to deal with it. The
> > text on the screen is very faint and many characters are scrambled as if
> > the beam was moving when the points where plotted. When typing there is a
> > flash of the beam which is then stored as the scrambled text.
> >
> > http://i.imgur.com/iQhQW67.jpg
> >
> > It probably reads "SYNTAX ERROR" something on the screen.
> >
> > My experience with DVST device is minimal. I used an old Philips storage
> > oscilloscope many years ago but I don't remember the screen to be this
> > dull.
> >
> > It seems like the storage system is not at full output. Unfortunately I
> am
> > not getting a good understanding on how the DVST system works from
> reading
> > the service manual. What is the purpose of the timers for cursor and
> > character intensity?
> >
> > I am about to check all the voltages related to the display mentioned in
> > the calibration section of the manual, but just in case someone directly
> > recognize what kind of problem there is I would be much interested.
> >
> > /Mattis
> >
> >

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