Tek 7844 Alphanumeric Display Issues


Liam Perkins
 

I have a 7844, ser. no. B173417, that works fine but for the character
display which is shifted upward 5 divisions, making of course the top
portion of the display invisible.

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 driver hardware; a) the initial ROM-based
all-analogue, b) the late-80s 2732 EPROM-based system instead of the
earlier analogue ROMS and, c) a third generation readout board designed
around an 80C31 micro‚Äźcontroller.

Mine is the EPROM version and despite buying hard copy off eBay and
downloading everything off 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 what is the problem.

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

TIA
Liam @ PEARL, Inc.


 

We already replied to you that the fault is most likely to be in the auxiliary input of the 2nd Vertical amplifier, and that the readout vertical position pot is R2700 on the vertical amplifier board.

If you are asking where to find schematics of the EPROM version of the readout board, I can't help, but none of the original boards had a vertical position pot on the RO board, and none of the later 80C31 versions did either, so its my bet that the EPROM version also didn't.

David

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Liam Perkins
Sent: 22 April 2021 05:34
To: TekScopes@groups.io
Subject: [TekScopes] Tek 7844 Alphanumeric Display Issues

I have a 7844, ser. no. B173417, that works fine but for the character
display which is shifted upward 5 divisions, making of course the top
portion of the display invisible.


 

On Mon, Apr 26, 2021 at 10:56 AM, David C. Partridge wrote:


If you are asking where to find schematics of the EPROM version of the readout
board, I can't help
The RO board wasn't unique to the 7844. I'm pretty sure that some later 7904A's had the same board. I guess (free) SM's are available. I'd look for schematics there.
Just checked: My (ArtekManual's) 070-4593-00 contains two RO versions; one of them is the EPROM-one.

Raymond