Re: 067-0912-00 needed
Dave,toggle quoted messageShow quoted text
The board is weird. My understanding of this is all this board does is allow you to check the lights “I know mine are ok” and it passes analog signals to the tube amplifiers so you can calibrate the analog portions of the scope with out any of the digital circuits being installed.
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Dave Casey
Sent: Thursday, October 22, 2020 4:48 AM
Subject: Re: [TekScopes] 067-0912-00 needed
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
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...
On Wed, Oct 21, 2020 at 1:12 PM Dave Daniel <firstname.lastname@example.org> wrote:
A schematic for the -00 version of the board is in the datasheet link