Tektronix 4051 repair.

Mattis Lind mattislind at gmail.com
Thu Sep 22 01:31:49 CDT 2016

2016-09-21 22:27 GMT+02:00 Pete Lancashire <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 also think it is a analog problem. But since I don't understand how it
works I cannot pin point where. There are two potentiometers (conveniently
located underside the machine...) that controls the character intensity
timer and cursor intensity timer. "Intensity timer": how is that supposed
to work?

I don't think the Char Gen ROM is bad. I have seen perfectly drawn
characters. The deflection probably works to since I was able to fill the
entire screen with garbage.

Timing problem. Yes. Since it often enable the beam when just starting to
deflecting it I think that there is some analog timing circuitry that
doesn't behave well. This gives the effect of some lines are drawn from the
center of the screen.

I should have made a short video since it probably give a better idea what
is going on.

> When you hit the erase what happens ?

It erases the screen as expected.


> -pete
> On Wed, Sep 21, 2016 at 12:07 PM, Mattis Lind <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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