Tek 7844 Alphanumeric Display Issues


Liam Perkins
 

I have a 7844, ser. no. B173417, that works fine but for the readout
display which is shifted upwards 5 divisions, puting the top half of
the display off the screen.

According to the 7K-series Readout System on the TekWiki here:

https://w140.com/tekwiki/wiki/7000_series_readout_system

there were three versions of the readout display hardware; a) the
initial all-analogue, ROM-based version, b)the late-80s 2732
EPROM-based version and, c) a third generation readout designed around
an 80C31 micro-controller.

Mine is the EPROM version and despite buying a hard copy manual off
eBay and downloading everything from the TekWiki I cannot find a
manual describing my unit so I don't know where to find the pots
that'll put the display where it belongs; assuming that's the problem.
I've fiddled the pots on the EPROM board and found only one that
effects the readout, by changing the character size.

Does anyone have any experience with this, or access to the correct
manual or the version number of same ?

TIA
Liam @ PEARL, Inc.


Mark Vincent
 

Liam,

Look on the vertical board mounted to the center support facing the right side of the scope. It will be on the same side as the readout board. There is a ro cent. control in the center of the three pots at the top of the board. That is likely the cause for the readout problem.

Mark


 

Readout position should be controlled by a pot (r2700) on the Beam 2 vertical boards.

Sounds most likely you have a problem with the auxiliary input amplifier on the Beam 2 vertical board. Maybe that pot is OC?

See Pages 3-24 and on, 5-35 and on and schematic <10>

David.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Liam Perkins
Sent: 22 April 2021 19:00
To: tekscopes@groups.io
Subject: [TekScopes] Tek 7844 Alphanumeric Display Issues

I have a 7844, ser. no. B173417, that works fine but for the readout
display which is shifted upwards 5 divisions, puting the top half of
the display off the screen.

According to the 7K-series Readout System on the TekWiki here:

https://w140.com/tekwiki/wiki/7000_series_readout_system

there were three versions of the readout display hardware; a) the
initial all-analogue, ROM-based version, b)the late-80s 2732
EPROM-based version and, c) a third generation readout designed around
an 80C31 micro-controller.

Mine is the EPROM version and despite buying a hard copy manual off
eBay and downloading everything from the TekWiki I cannot find a
manual describing my unit so I don't know where to find the pots
that'll put the display where it belongs; assuming that's the problem.
I've fiddled the pots on the EPROM board and found only one that
effects the readout, by changing the character size.

Does anyone have any experience with this, or access to the correct
manual or the version number of same ?

TIA
Liam @ PEARL, Inc.