21 Sep
2016
21 Sep
'16
11:31 p.m.
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.
/Mattis
-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