Re: 067-0912-00 needed

Dave Casey

That schematic has some curious idiosyncrasies. The logic is powered by
+5VD, but all the pull ups being used are to +5V. (The ones that are shown,
anyway; there are unused inputs on U420 and U520 that must also be pulled
high for the board to work, but these aren't indicated in the schematic.)
Also, the inputs from the mode switches on A2 are referenced to +5V (not
+5VD). +5V and +5VD are basically two copies of the same supply, powered
from the same output of the switcher, and their domains cross in a few
places within the scope without any real decoupling. That spirit continues
in the 067-0912-00 board.

The parts list and schematic do not appear to line up 1:1 (C621 on the
schematic is very probably C620 on the parts list, but R520 is in the parts
list and so far escapes detection on the schematic.

Another interesting observation is that the _FPR ("Front Panel Read",
active low) signal is left floating when using the 067-0912-00, meaning
that A2U61 and A2U62 are not guaranteed to be tri-stated and could be
fighting U430 and U530 of the 067-0912-00 for D0:D8. I'm sort of surprised
there's no pull-up on the A2 board, but the schematic shows that signal
being driven directly by the MPU board (which would be absent when using
the 067-0912-00).

Enough mysteries for tonight...

Dave Casey

On Wed, Oct 21, 2020 at 1:12 PM Dave Daniel <> wrote:

A schematic for the -00 version of the board is in the datasheet link on
the TekWiki page to which Dennis pointed.


On Oct 21, 2020, at 13:45, Dennis Tillman W7pF <>

Hi Eric,
I can't help with a schematic, but there is some information on this
card on TekWiki at
Dennis Tillman W7pF

-----Original Message-----
From: [] On Behalf Of Eric
Sent: Wednesday, October 21, 2020 8:55 AM
Subject: [TekScopes] 067-0912-00 needed

I am thinking about trying to tackle a calibration on my 7854. I have
confirmed that the digital and analog sections are out of adjustment. The
digital section is about .8 division left of center. In looking through the
calibration document It seems I have everything I need to do the
calibration except the 067-0912-00 the analog test board. How likely is
this something that I am going to be able to acquire it does not look too
complex from the schematic just a few IC’s and a data bus.

Dennis Tillman W7pF
TekScopes Moderator

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